Tag Archives: dark matter

Illustration showing snapshots from a simulation by astrophysicist Volker Springel of the Max Planck Institute in Germany. It represents the growth of cosmic structure (galaxies and voids) when the universe was 0.9 billion, 3.2 billion and 13.7 billion years old (now). Image via Volker Springel/ MPE/Kavli Foundation.

What Is Dark Energy?

During the 20th century, the idea that the Universe existed in a steady state was seriously challenged and eventually dismissed by the discovery that the Universe is not only expanding but is also doing so at an accelerating rate. The reason for this accelerating expansion is thus far unknown, but scientists have given this force a name–albeit one that is a placeholder–dark energy.

Explaining this accelerating rate of expansion has become one of the most challenging problems in cosmology. The fact that the value for this acceleration varies wildly between theory and practical observations has created a raft of problems in itself. This means that the net result arising from any attempt to explain dark energy creates more questions than it answers.

Dark Energy: The Basics

Illustration showing snapshots from a simulation showing the growth of cosmic structure (galaxies and voids) when the universe was 0.9 billion, 3.2 billion and 13.7 billion years old (now). (Volker Springel/ MPE/Kavli Foundation)

Dark energy is whatever is causing the expansion of the Universe to accelerate. One of the most striking things about this mysterious energy is just how much ‘stuff’ in the Universe it accounts for. If you consider the contents of the cosmos to be matter and energy –more formally known as the Universe’s mass-energy density–then dark energy accounts for between 68% to 72% of all cosmic ‘stuff.’

Dark matter is the second-largest contributor, with just a tiny proportion of the Universe’s ‘stuff’ made up of the baryonic matter consisting of atoms that we see around us on a day-to-day basis.

This is even more staggering when you consider that all the stars, planets, dust, gas and cosmic bodies that make up the visible Universe are contained in this tiny fraction of cosmic stuff that doesn’t even amount to 5% of the Universe’s contents.

Dark energy could very roughly be described as a force acting in opposition to gravity. Whereas the more familiar everyday force of gravity holds objects like planets and stars together in orbits, dark energy acts as a repulsive force, driving galaxies themselves apart. But, whereas gravity acts upon objects themselves, dark energy acts on the very fabric of spacetime between objects. Because dark matter is the largest contributor to gravity, this means this mysterious substance is locked in what has been termed a ‘cosmic tug of war.’ And it’s clear during our current epoch, dark energy is winning!

A popular analogy for this is the description of the Universe as the surface of a balloon. Galaxies are represented by two marker ink dots on this surface. As the balloon is inflated the points move apart with the very space between them expanding.

Repeat the experiment with three unevenly placed dots and it is clear that the dots that are initially further apart recede away from each other more rapidly. This extremely rough analogy carries over to galaxies. The further apart the galaxies are, the more quickly they recede.

The expanding universe as the surface of a balloon (Bianchi, E., Rovelli, C. & Kolb, R. Is dark energy really a mystery?. Nature 466, 321–322 (2010). https://doi.org/10.1038/466321a)

An Expanding Surprise


The discovery that the Universe is expanding came as a considerable shock to the scientific community when it was confirmed by Edwin Hubble in 1929. Hubble had built upon theory provided by George Lemaitre and Alexander Friedman who had used the equations of general relativity to predict that the Universe was non-static, something that very much contradicted the scientific consensus of the time.

Ann Field STScl

Albert Einstein who devised general relativity had also found that his geometric theory of gravity predicted a non-static Universe, something he wasn’t exactly comfortable with. Despite having already killed many of the sacred cows of physics, Einstein was unwilling to do away with the concept of a static Universe. To recover a static Universe that was neither expanding nor contracting, the world’s most famous scientist introduced to his equations a ‘fudge factor’ called the cosmological constant–commonly represented with the Greek letter lambda.

The cosmological constant was in danger from the start. Once Hubble managed to persuade Einstein that the Universe was indeed expanding, the physicist abandoned the cosmological constant, allegedly describing it as his ‘greatest blunder’ in his later years. The cosmological constant wouldn’t stay in the cosmological dustbin for very long, however.

If physicists had been surprised by the discovery at the beginning of the 20th Century that the Universe is expanding, they would be blown away when at the end of that same century when the observations of distant supernovae made by two separate teams of astronomers revealed that not only is the Universe expanding, it is doing so at an accelerating rate.

To understand why this is shocking and how it leads to the conclusion that some repulsive force is driving this expansion, it is necessary to journey to the very beginning of time… Let’s take some balloons too…

Escaping the Big Crunch

A diagram of the expansion of the Universe. This accelerating expansion of the Universe could be explained by an early dark energy model. (NASA/ WMAP Team). Credit: NASA

When thinking about the initial expansion of the Universe it makes sense to conclude that the introduction of an attractive force within that Universe would slow and eventually halt this expansion. That is exactly what gravity should do, and it seems did do during the early stages of expansion that had nothing to do with dark energy (we think).

Some cosmologists are willing to go a step further. If there is no outward pressure but an inward attractive force, shouldn’t the Universe actually start to contract?

This leads to the theory that the Universe will end in what physicists term the ‘Big Crunch’–an idea that dark energy could make obsolete. Think about how counter-intuitive this was to scientists when the idea was first suggested and evidenced. Let’s return to the balloon analogy; imagine you stop blowing into the balloon, and instead start sucking the air out of it.

How shocked would you be to find that the balloon isn’t contracting, it’s continuing to expand? And not just that, it’s actually expanding faster than it was when you were blowing into it!

With that in mind, consider the initial moments of the Universe. Beginning in an indescribably dense and hot state, squeezed into a quantum speck, the Universe undergoes a period of rapid expansion. This period of expansion wasn’t driven by dark energy. As it expands, the Universe cools allowing electrons to form atoms with protons and neutrons, which in turn frees photons to travel the cosmos.

Soon there is enough matter in the Universe to allow the attractive force of gravity to slow its expansion. And this does seem to be what happened in the early cosmos. The rapid inflation of the infant Universe is believed to have halted at around 10 -32 seconds after the Big Bang, with the Universe still expanding, albeit at a much slower rate.

Euclid Assessment Study Report



This period of expansion continued to slow as a result of the growing dominance of matter during what cosmologists call the ‘matter-dominated epoch.’ But, at around 9.8 billion years into the Universe’s 13.8 billion year history, something strange begins to happen. The Universe begins to expand again, this time at an accelerating rate.

This is the dawn of the dark energy dominated epoch.

The Cosmological Constant is Back and Still Causing Trouble

Observations of the redshift of distant supernovae in the later 1990s showed cosmologists that not only was the Universe expanding, but it was doing so at an accelerating rate. (ESO)

That explains why the accelerating expansion of the Universe is so troubling and the need to introduce the placeholder concept of dark energy to explain it. Yet this accelerating expansion would still need a mathematical representation in equations used to describe the Universe. To do this cosmologists would return to the cosmological constant and its symbol, lambda.


This new iteration of the cosmological constant would be used in a different way to Einstein’s version. Whereas the earlier cosmological constant was used to balance gravity and hold the Universe steady and static, this new version would be used to overwhelm gravity and account for the acceleration of its expansion. But, this revised use of the cosmological constant does not mean it is any less troublesome than Einstein had found its predecessor.

In fact, the difference between the cosmological constant’s measured value, found by measuring the redshift of distant Type Ia supernovae, diverges from the value predicted by quantum field theory and particle physics by a value as large as 10121 (that’s 1 followed by 121 zeroes). Thus, it should come as no surprise that this value has been described as the worst prediction in the history of physics.

And as it represents the action of dark energy, that makes dark energy itself cosmology’s biggest conundrum.

OK… But What is Dark Energy?

So by now, you might well be thinking all of this is all fine and good, but this article specifically asks ‘what is dark energy?’ Isn’t it time to get to answering this question? It should come as no surprise that the answer is no one knows. But, that doesn’t mean that cosmologists don’t have some very good ideas.

One of the explanations for dark energy says that it could be vacuum energy, an underlying background energy that permeates that Universe and is represented by the cosmological constant. The most commonly cited evidence for vacuum energy–the energy of ’empty’ space which manifests as the Casimir effect.

Without delving too deeply into this, as relativity states that energy and mass are equivalent and mass has gravitational effects, then it stands to reason if empty space has vacuum energy, this too should contribute to the effect of gravity across the cosmos. That contribution has been factored in as a negative repulsive influence acting against the attractive influence of gravity.

Many explanations for dark energy exist, including the possibility that general relativity is incorrect and dark energy doesn’t exist at all.

The big problem with this is that quantum field theory suggests that this negative pressure contribution from vacuum energy should arise from all particles and thus, should give lambda a value that is tremendously larger than that obtain when our astronomers measure the redshift of Type Ia supernovae in distant galaxies.

This problem could be solved by dark energy’s effects being the result of something other than vacuum energy, of course. The Universe’s accelerating expansion could be due to some, as of yet undiscovered fundamental force of nature. Alternatively, it could indicate that our best current theory of gravity–general relativity– is incorrect.

A new generation of cosmologists is currently actively tackling the dark energy puzzle with new and revolutionary ideas. These include the idea that dark energy could have started work in the early Universe, an idea proposed by Early Dark Energy (EDE) models of the Universe. Another alternative is that dark energy does not influence the curvature of the Universe, or perhaps does so weakly–a theory referred to as the ‘well-behaved cosmological constant.’

As unsatisfying an answer as it is, the only honest way of addressing the question ‘what is dark energy?’ right now is by saying; we just don’t know. But, science wouldn’t be anywhere near as fascinating without mysteries to solve, and revolutionary ideas to be uncovered.

Ten areas in the sky were selected as “deep fields” that the Dark Energy Camera imaged several times during the survey, providing a glimpse of distant galaxies and helping determine their 3D distribution in the cosmos.

Astronomers map over 100 million galaxies to crack dark matter and dark energy puzzle

The Dark Energy Survey (DES) is an ambitious cosmological project that aims to map hundreds of millions of galaxies. In the process, the project will detail hundreds of millions of galaxies, observe thousands of supernovae, map the cosmic web that links galaxies, all with the aim of investigating the mysterious force that is causing the Universe to expand at an accelerating rate.

Using the 570-megapixel Dark Energy Camera on the National Science Foundation’s Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), Chile, the DES has observed a map of galaxy distribution and morphology that stretches 7 billion light-years and captures 1/8 of the sky over Earth.

Ten areas in the sky were selected as “deep fields” that the Dark Energy Camera imaged several times during the survey, providing a glimpse of distant galaxies and helping determine their 3D distribution in the cosmos.
Ten areas in the sky were selected as “deep fields” that the Dark Energy Camera imaged several times during the survey, providing a glimpse of distant galaxies and helping determine their 3D distribution in the cosmos. The image is teeming with galaxies — in fact, nearly every single object in this image is a galaxy. Some exceptions include a couple of dozen asteroids as well as a few handfuls of foreground stars in our own Milky Way. (Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA)



Now new results from the DES which collects the work of an international team of over 400 scientists from over 25 institutions from countries including the US, UK, France, Spain, Brazil, and Australia, are in. The findings are detailed in a ground-breaking series of 29 papers and comprises of data collected during the DES’ first three years of operation providing the most detailed description of the Universe’s composition and expansion to date.

The Víctor M. Blanco 4-meter Telescope is seen here at night at Cerro Tololo Inter-American Observatory, with trails of stars high above it. On this telescope is the 570-megapixel Dark Energy Camera — one of the most powerful digital cameras in the world. The Dark Energy Camera was designed specifically for the Dark Energy Survey. It was funded by the Department of Energy (DOE) and was built and tested at DOE’s Fermilab. (DOE/FNAL/DECam/R. Hahn/CTIO/NOIRLab/NSF/AURA)

The survey was conducted between 2013 to 2019 cataloging hundreds of millions of objects, with the three years of data covered in these papers alone containing observations of at least 226 million galaxies observed over 345 nights.

The fact that some of these galaxies are close to the Milky Way and others are much more distant–up to 7 billion light-years away– gives researchers an excellent picture of the evolution of the Universe over around half of its lifetime.

The results seem to confirm the standard model of cosmology, currently the best-evidenced theory of the Universe’s composition and evolution which suggests the Universe was created in a ‘Big Bang’ event and has a composition of 5% ordinary or baryonic matter, 27% dark matter, and 68% dark energy.

The snapshot of the Universe provided by the DES does seem to show that the Universe is less ‘clumpy’ than current cosmological models suggest, however.

Illuminating the Dark Universe

The fact that the ‘Dark Universe’ consists of 95% of the matter and energy in the known cosmos means that there are huge gaps in our understanding of the evolution of the Universe, its past, present, and its future.

These gaps include the nature of dark matter, whose gravitational influence holds galaxies together, and dark energy, the force that is expanding space between the galaxies driving them apart at an accelerating rate.

These effects seem to be in opposition, with one holding matter together and the other working upon space itself to drive matter apart. And it is this cosmic struggle that shapes the Universe which the DES aimed to investigate.

There are two key phenomena which the survey used to do this. Studying ‘the cosmic web’ that links galaxies together in clusters and loose associations gives hints at the distribution and influence of dark matter.

The Dark Energy Survey camera (DECam) at the SiDet clean room. The Dark Energy Camera was designed specifically for the Dark Energy Survey. It was funded by the Department of Energy (DOE) and was built and tested at DOE’s Fermilab. (DOE/FNAL/DECam/R. Hahn/CTIO/NOIRLab/NSF/AURA)



The second phenomenon used by the DES is the bending of light as it travels past curvatures in spacetime created by objects of tremendous mass like galaxies. This effect predicted by Einstein’s theory of gravity–general relativity–is known as ‘gravitational lensing.’

The DES relied on a form of this effect called ‘weak gravitational lensing’ to assess how dark matter is distributed across the Universe, thus inferring its ‘clumpiness.’

Weak graviational lensing was one ofthe phenomenna that teh DES took advantage of to investigation dark matter distributions (ESA)

The data collected by the DES was cross-referenced against measurements carried out by the European Space Agency (ESA) operated mission, the Planck observatory. The orbiting observatory, which operated between 2009 and 2013 and studied the cosmic background radiation (CMB)–an imprint leftover from an event shortly after the Big Bang in which electrons and protons connected thus allowing photons to travel freely for the first time.

Observing the CMB reveals conditions that were ‘frozen in’ to it at the time of this event known as the last scattering and thus gives a detailed picture of the Universe when it was just 400 thousand years old for the DES team to draw from.

Setting the Scene for Future Surveys

The DES intensely studied ten regions labeled as ‘deep fields’ which were repeatedly imaged during the course of the survey. These images were stacked which allowed astronomers to observe distant galaxies.

In addition to allowing researchers to see further into the Universe and thus further back in time, information regarding redshift– an increase in wavelength caused by objects receding which can arise as a result of the Universe’s expansion–taken from these deep fields was used to calibrate the rest of the survey. This constituted a major step forward for cosmic surveys providing the researchers with a picture of the Universe painted with stunning precision.

Whilst the DES was concluded in 2019, the sheer wealth of data collected by the survey requires a huge amount of computing power and time to assess. This is why we are only seeing the first three years of observations reported and likely means that the DES still has much more to deliver.

The Vera C Rubin Observatory currently under construction in Chile will pick up where the DES leaves off (LSST Collaboration)

This will ultimately set the scene for the Legacy Survey of Space and Time (LSST) which will be conducted at the Vera C Rubin observatory–currently under construction on the El Penon peak of Cerro Pachon in northern Chile.

Whereas the DES surveyed an inarguably impressive 1/8 of the sky over the earth, the wide-field camera that will conduct the LSST will capture the entire sky over the Southern hemisphere, meaning it will view half of the entire sky over our planet.

A major part of the LSST’s mission will be the investigation of dark matter and dark energy, meaning that when the data from the DES is finally exhausted and its secrets are revealed, a worthy successor will be waiting in the wings to assume its mission of discovery.

What is dark matter? A deep dive

If you’ve been following our space articles, you may have come across something called “dark matter”. It’s the most abundant type of matter in the universe — our best models have established that dark matter comprises 84.4% of the matter contained in the known universe — but we still don’t really understand just what it is. Dark matter is something that we know is out there, but we have little idea what it’s made of.

Credit: News-G.

Wait, so how do we know it’s even real?

“Regular” matter (technically called baryonic matter) is made of electrons, protons, and neutrons. Cosmologists define the three particles as baryons –technically speaking, electrons are something else, but that’s beside the point here. Baryons make up gas, gas makes up stars, stars go boom and make planets and other things — including you. Yes, you are made of star stuff — baryonic star stuff, to be precise.

All this is done thanks to the electromagnetic (EM) force that forms chemical bonds, glueing regular atoms together But Dark Matter (DM) plays a different game.

Dark matter doesn’t interact with things the way baryonic matter does. It doesn’t scatter or absorb light, but it still has a gravitational pull. So if there are beings made of dark matter living right here, right now, you probably wouldn’t even know it because the perception of touch is felt when your sensory nerves send the message to your brain, and these nerves work thanks to the EM force.

We can’t touch dark matter, and no optical instruments can detect, so how do we ‘see’ it? Indirectly, for starters. Look for gravity, if there isn’t enough visible mass to explain to explain the gravitational pull felt by a region of the universe, then there something there. Invisible does not mean non-existant. If it weren’t for its gravity effect, there would be little indication of dark matter existing.

The main observational evidence for dark matter is the orbital speeds of stars in the arms of spiral galaxies. If Kepler and Newton were correct, stars’ velocity would decrease with the orbital radius in a specific way. But this was not observed by Vera Rubin and Kent Ford, who tracked this relationship. Instead, Rubin and Ford got a velocity vs radius relation that looked like the stars had a nearly constant behavior from a certain point of the galactic orbit.

This could only be explained if there would be a lot more matter somewhere that we’re not seeing. Something was pulling at these stars gravitationally, and that something is dark matter.

Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). Dark matter can explain the ‘flat’ appearance of the velocity curve out to a large radius. Credits: Phil Hibbs.

Another important evidence of dark matter comes from galaxy superclusters like 1E 0657-558. Astronomers observed that within this cluster, there are two groups of galaxies placed in a peculiar position to one another. 

If you look at the Hubble Space Telescope image below (1st and 2nd), you’ll notice that there are many galaxies on the left and another group on the opposite side. When astronomers observed in X-ray, they concluded that these two clusters collided and left a gas trace of the shock. The faster cluster was like a bullet (it’s even named the Bullet Cluster) passing through the slower one at around 3000–4000 km/s nearly 100-200 million years ago (3rd pic).

Visible light image from the Hubble Space Telescope, NASA, ESA and the Magellan Telescope, University of Arizona
Visible light image from the Hubble Space Telescope, NASA, ESA and the Magellan Telescope, University of Arizona
X-ray light image from the Chandra X-ray Observatory: NASA, CXC

But one of the most convincing evidence of dark matter came with gravitational lensing.

Scientists used gravitational lensing to estimate the mass of the objects involved in the collision. They found that the galaxies which hadn’t collided agreed with the weak lensing detections. This indicates those galaxies are ahead of ‘the X-ray evidence’ (below, 1st image). Since dark matter doesn’t interact with nearly anything, in this phenomenon, we see a bunch of mass (blue) moving faster than the gas (purple), barely affecting the baryonic matter (2nd image).

Dark matter map: NASA, STScI; ESO; University Arizona
Composite image (visible, dark matter map, X-ray): NASA, ESA, ESO, University Arizona

So what is Dark Matter?

Just because we don’t know what dark matter is doesn’t mean we have no idea. In fact, researchers have a few theories and are considering several plausible candidates.

There are three ways to classify dark matter. Cold dark matter describes the formation of the large-scale structure of the universe and is the fundamental component of the matter in the universe. It’s called cold because it moves ‘slowly’ compared to the speed of light.

Weakly interacting massive particles (WIMPs) are the candidates for cold dark matter particles. They supposedly interact via weak nuclear force. The particles which belong to this group are thought to be the lightest particles of the supersymmetric theories. Neutral examples of these particles could have been produced in the early universe, and later participated in the formation of galaxy clusters.

Hot dark matter is the opposite, it moves close to the speed of light. The warm candidate particles are thought to be less interactive than neutrinos.

Another candidate particle for dark matter is the sterile neutrino — a hypothetical particle that interacts only via gravity and not via any of the other fundamental forces. These would be responsible for forming warm dark matter. They also seem to be heavier than the standard neutrino, and have a longer lifetime before they break down.

Neutrinos were thought to be the best candidates for dark matter. Neutrinos are weird particles — they barely interact with things, and even then only gravitationally (which is a weak interaction). Besides, they do not possess electrical charge, which is why they do not interact electromagnetically. However, the neutrino temperature is high and they decouple (stop interacting with other forms of matter) only at relativistic velocities. If dark matter was made of neutrinos, the universe would have looked radically different.

Massive Compact Halo Objects (MACHOs) represent a different type of candidate. They’re no WIMPs at least. They aren’t particles either, but rather brown dwarfs, planets like Jupiter, black holes in galactic haloes. The best possible MACHOs are primordial black holes( PBHs). Different from the ordinary black holes we see in the center of galaxies, PBHs are thought to have been created nearly 10 seconds after the Big Bang. No evidence for such objects has yet been discovered, but it’s still an open possibility.

Detecting dark matter

Many ideas for the detection of each plausible candidate have been developed.

Through cosmology, the main evidence comes from the Cosmic Microwave Background (CMB).  Yes, the same radiation Dr. Darcy Lewis detected (for real) in the TV miniseries WandaVision. It is the remnant electromagnetic radiation from when the universe was a 380,000-year-old baby.

The best CMB observations we have currently are from the Planck satellite 2018 survey. Different amounts of matter have distinct signals in the CMB observations, forming the temperature power spectrum.

Four Possible Models of the Universe. The yellow square marks the present in all four cases, and for all four, the Hubble constant is equal to the same value at the present time. Time is measured in the vertical direction. The first two universes on the left are ones in which the rate of expansion slows over time. The one on the left will eventually slow, come to a stop and reverse, ending up in a “big crunch,” while the one next to it will continue to expand forever, but ever-more slowly as time passes. The “coasting” universe is one that expands at a constant rate given by the Hubble constant throughout all of the cosmic time. The accelerating universe on the right will continue to expand faster and faster forever. Credits: Physics LibreTexts.

If the theory is correct, the shape of the power spectrum is different for different amounts of matter. There’s such a thing known as the critical density of the universe, which describes the density of the universe if it was coasting, expanding but not accelerating, and if it stopped its expansion. When you divide the density of the observable matter by the critical density, you get its density parameter (Ω).

The temperature power spectrum is modeled according to the different amounts of ingredients in the universe, more matter or less matter changes its shape. Planck’s observations have shown that the matter density parameter is Ω h² ~0.14, so if the shape of the graph corresponds to that value we have evidence of the amount of dark matter in the universe.

Temperature power spectrum for different matter densities. Credits: Wayne Hu.

There are also ways to detect dark matter directly, not through cosmology but through particle physics. The Large Hadron Collider (LHC) is the most powerful particle accelerator, can collide protons at extremely high (relativistic) speeds, generating a bunch of scattered particles that are then measured by the detectors.

Physicists hope to find dark matter by comparing the energy before and after the collision. Since the dark matter particles are elusive, the missing energy could explain their presence. However, no experiment has observed dark matter so far — though researchers are still looking.

Another underground experiment uses high purity sodium iodide crystals as detectors. The detectors at DAMA/LIBRA (Large sodium Iodide Bulk for RAre processes), for example, try to observe an annual variation of regular matter colliding with WIMPs due to the planet’s motion around the Sun which means we’re changing our velocity relative to the galactic dark matter halo. The problem is that DAMA’s 20 years’ worth of data didn’t have enough statistical significance. However, in an identical experiment meant to directly detect dark matter, called ANAIS (Annual modulation with NaI Scintillators), in 3 years scientists gathered more reliable data indicating this method is not conducive to finding dark matter anytime soon. 

To get a better picture of the challenge in having a conclusive result, take a look at the image below. All those lines and colorful contours represent the results of different experiments, none of them seem to agree. That’s the problem with dark matter, we still don’t have the evidence to match any theory we came up with — and we can’t really rule out any possibilities either.

WIMP discovery limit (thick dashed orange) compared with current limits
and regions of interest. Credits: J. Billard and E. Figueroa-Feliciano.

The questions of what dark matter is and how it works still have no satisfying answer. There are many detection experiments being planned and conducted in order to explain and verify different hypotheses, but nothing conclusive thus far. Let’s hope we don’t have to wait another 20 years to figure out if one experiment is right or wrong. Unfortunately, groundbreaking discoveries can take a lot of time, especially in astrophysics. While we wait, dark matter will continue to entertain our imagination.

The article was primarily based on the 2020 Review of Particle Physics from Particle Data Group’s Dark Matter category.

This NASA/ESA Hubble Space Telescope image shows the massive galaxy cluster MACSJ 1206. Embedded within the cluster are the distorted images of distant background galaxies, seen as arcs and smeared features. These distortions are caused by the dark matter in the cluster, whose gravity bends and magnifies the light from faraway galaxies, an effect called gravitational lensing. This phenomenon allows astronomers to study remote galaxies that would otherwise be too faint to see. (NASA, ESA, G. Caminha (University of Groningen), M. Meneghetti (Observatory of Astrophysics and Space Science of Bologna), P. Natarajan (Yale University), the CLASH team, and M. Kornmesser (ESA/Hubble))

Astronomers Investigate Dark Matter’s Missing Ingredient

Our understanding of dark matter and its behavior could be missing a key ingredient. More gravitational lensing, the curving of spacetime and light by massive objects, could lead to the perfect recipe to solve this cosmic mystery. 

Despite comprising anywhere between 70–90% of the Universe’s total mass and the fact that its gravitational influence literally prevents galaxies like the Milky Way from flying apart, science is still in the dark about dark matter

As researchers around the globe investigate the nature and composition of this elusive substance, a study published in the journal Science suggests that theories of dark matter could be missing a crucial ingredient, the lack of which has hampered our understanding of the matter that literally holds the galaxies together. 

The presence of something missing from our theories of dark matter and its behavior emerged from comparisons of observations of the dark matter concentrations in a sample of massive galaxy clusters and theoretical computer simulations of how dark matter should be distributed in such clusters. 

Astronomers measured the amount of gravitational lensing caused by this cluster to produce a detailed map of the distribution of dark matter in it. Dark matter is the invisible glue that keeps stars bound together inside a galaxy and makes up the bulk of the matter in the Universe. (NASA, ESA, G. Caminha (University of Groningen), M. Meneghetti  (Observatory of Astrophysics and Space Science of Bologna), P. Natarajan (Yale University), and the CLASH team.)


Using observations made by the Hubble Space Telescope and the Very Large Telescope (VLT) array in the Atacama Desert of northern Chile, a team of astronomers led by Massimo Meneghetti of the INAF-Observatory of Astrophysics and Space Science of Bologna in Italy have found that small-scale clusters of dark matter seem to cause lensing effects that are 10 times greater than previously believed.

“Galaxy clusters are ideal laboratories in which to study whether the numerical simulations of the Universe that are currently available reproduce well what we can infer from gravitational lensing,” says Meneghetti. “We have done a lot of testing of the data in this study, and we are sure that this mismatch indicates that some physical ingredient is missing either from the simulations or from our understanding of the nature of dark matter.”

Just Add Gravitational Lensing

The lensing that the team believes accounts for dark matter discrepancies is a factor of Einstein’s theory of general relativity which suggests that gravity is actually an effect that mass has on spacetime. The most common analogy given for this effect is the distortion created on a stretched rubber sheet when a bowling ball is placed on it.

This effect in space that results from a star or even a galaxy curving space and thus bending the path of light as it passes the object. Otherwise known as gravitational lensing it is commonly seen when a background object–which could be as small as a star or as large as a galaxy– moves in front of a foreground object and curves light from it giving it an apparent location in the sky. 

The gravitational lensing of a distant quasar by an intermediate body forms a double image seen by astronomers on Earth. (Lambourne. R, Relativity, Gravitation and Cosmology, Cambridge Press, 2010)

In extreme cases, where this lensing causes the paths of light to change in such a way that its arrival time at an observer is different, it can cause a background object to appear in the night sky at various different points. A beautiful example of this is an Einstein ring, where a single object appears multiple times forming a ring-like arrangement.

Because dark matter only interacts via gravity, ignoring even electromagnetic interactions — hence why it can’t be seen — gravitational lensing is currently the best way to infer its presence and map the location of dark matter clusters in galaxies.

 Returning to the ‘rubber sheet’ analogy from above, as you can imagine, a cannonball will make a more extreme ‘dent’ in the sheet than a bowling ball, which in turn makes a bigger dent than a golf ball. Likewise, the larger the cluster of dark matter — the greater the mass — the more extreme the curvature of space and therefore, light.

The gravitational microlensing effect results from the bending of space-time near an object of given mass that is predicted by Einstein’s general theory of relativity. An object, such as a star, crossing our line of sight to a more distant source star will affect the light from that star just like a lens, producing two close images whose total brightness is enhanced. If the lensing star is accompanied by a planet, one can (potentially) observe not only the principal effect from the star, but also a secondary, smaller effect resulting from perturbation by the planet. ( Beaulieu et al)

But now imagine what would happen if the bowling ball on the rubber sheet was surrounded by marbles. Though their individual distortions may be small, their cumulative effect could be considerable. The team believes this may be what is happening with smaller clusters of dark matter. These small scale clumps of dark matter enhance the overall distortion. In a way, this can be seen as a large lens with smaller lenses embedded within it.

Cooking Up A High-Fidelity Dark Matter Map

The team of astronomers was able to produce a high-fidelity dark matter map by using images taken by Hubble’s Wide Field Camera 3 and Advanced Camera Survey combined spectra data collected by The European Southern Observatory’s (ESO) VLT. Using this map, and focusing on three key clusters — MACS J1206.2–0847, MACS J0416.1–2403, and Abell S1063 — the researchers tracked the lensing distortions and from there traced out the amount of dark matter and how it is distributed.

This image from the NASA/ESA Hubble Space Telescope shows the galaxy cluster MACS J0416.1–2403. A team of researchers used almost 200 images of distant galaxies, whose light has been bent and magnified by this huge cluster, combined with the depth of Hubble data to measure the total mass and dark matter content of this cluster more precisely than ever before. (ESA/Hubble, NASA, HST Frontier Fields)

“The data from Hubble and the VLT provided excellent synergy,” says team member Piero Rosati, Università Degli Studi di Ferrara in Italy. “We were able to associate the galaxies with each cluster and estimate their distances.”

This led the team to the revelation that in addition to the dramatic arcs and elongated features of distant galaxies produced by each cluster’s gravitational lensing, the Hubble images also show something altogether unexpected–a number of smaller-scale arcs and distorted images nested near each cluster’s core, where the most massive galaxies reside.

The team thinks that these nested lenses are created by dense concentrations of matter at the center of individual cluster galaxies. They used follow-up spectroscopic observations to measure the velocity of the stars within these clusters and through a calculation method known as viral theorem, confirmed the masses of these clusters, and in turn, the amount of dark matter they contain. 

Abell S1063, a galaxy cluster, was observed by the NASA/ESA Hubble Space Telescope as part of the Frontier Fields programme. The huge mass of the cluster acts as a cosmic magnifying glass and enlarges even more distant galaxies, so they become bright enough for Hubble to see. (NASA, ESA, and J. Lotz (STScI))

This fusion of observations from these different sources allowed the team to identify dozens of background lensed galaxies that were imaged multiple times. The researchers then took this high-fidelity dark matter map and compared it to samples of simulated galaxy clusters with similar masses, located at roughly the same distances.

These simulated galaxy clusters did not show the same dark matter cluster concentrations — at least not on a small scale that is associated with individual cluster galaxies. 

The discovery of this disparity should help astronomers design better computer simulation models and thus develop a better understanding of how dark matter clusters. This improved understanding may ultimately lead to the discovery of what this abundant and dominant form of matter actually is. 


Original research: Meheghetti. M., Davoli. G., Bergamini. P., et al, ‘An excess of small-scale gravitational lenses observed in galaxy clusters,’ Science, [2020], 

We might have a new dark matter candidate particle — and we’ve already discovered it before

This image, taken with the NASA/ESA Hubble Space Telescope, focuses on an object named UGC 695, which is located 30 million light-years away within the constellation Cetus (The Sea Monster), also known as The Whale. Credit: European Space Agency.

Most of the mass of the universe is invisible even to our most sensitive instruments. We have no idea what it actually looks like or what it’s made of, but this mysterious stuff must be out there. We’re sure of this because we can see its strong gravitational effect. What’s more, without it, the universe’s acceleration would have slowed down instead of accelerating as astronomers have observed.

Scientists refer to this elusive mass as dark matter and believe it outnumbers “normal” (read: visible) matter five to one. Now, a new study is proposing a candidate particle that might be part of dark matter.

What’s interesting about this particle is that researchers have already detected it in previous experiments.

Tangible dark matter?

We know more about what dark matter isn’t made of than what it is. Studies have shown that dark matter cannot be explained by baryons, antimatter, nor galaxy-sized black holes as had been proposed over the years.

Credit: ZME Science Data Vizualization Studios.

In order to explain dark matter, physicists have proposed a number of candidate particles, including axions, dark photons, weakly-interacting massive particles (WIMPs), and superheavy gravitinos.

All of these candidates are hypothetical, in the sense that they haven’t been confirmed experimentally. This makes this latest study even more intriguing. It suggests that dark matter may be made of d-star hexaquark — more formally, d*(2380) — a particle that was detected in experiments in 2014.

“The origin of dark matter in the Universe is one of the biggest questions in science and one that, until now, has drawn a blank,” said Daniel Watts, a nuclear physicist at the University of York in the UK and lead author of the new study.

“Our first calculations indicate that condensates of d-stars are a feasible new candidate for dark matter. This new result is particularly exciting since it doesn’t require any concepts that are new to physics.”

Instead of being made up of sets of three quarks, like is the case for protons and neutrons, d-stars are particles made of six quarks, hence the ‘hexaquark’.

This means d-stars are bosons that can form an exotic form of matter called Bose-Einstein condensate (BEC) when chilled to almost absolute zero.

BEC, also known as the fifth state of matter, was first predicted in the 1920s by Albert Einstein and Indian physicist Satyendra Bose but it wasn’t until very late in 1995 that scientists were able to produce the necessary conditions for this extreme state of matter to occur. 

At room temperature, atoms are incredibly fast and behave akin to billiard balls, bouncing off each other when they interact. As you lower the temperature (remember temperature reflects atomic agitation or vibration), atoms and molecules move slower. Eventually, once you get to about 0.000001 degrees above absolute zero, atoms become so densely packed they behave like one super atom, acting in unison. 

The physicists at the University of York propose that soon after the Big Bang, conditions would have been enough for d-star hexaquarks to come together as BECs. And, according to their calculations, if the particles gathered in large enough numbers, they could have potentially caused analogous effects to dark matter.

In the future, the researchers plan on testing their hypothesis in a laboratory setting. Meanwhile, they hope astronomers can join in and search for signals that may indicate d-star BECs somewhere in the galaxy or beyond.

“The next step to establish this new dark matter candidate will be to obtain a better understanding of how the d-stars interact – when do they attract and when do they repel each other,” said Mikhail Bashkanov, co-author of the study. “We are leading new measurements to create d-stars inside an atomic nucleus and see if their properties are different to when they are in free space.”

The findings were reported in the Journal of Physics G: Nuclear and Particle Physics.

Dark matter is colder than we thought — and we know this thanks to Einsteins crosses

Clumps of dark matter can be surprisingly small — and cold.

Researchers were able to indirectly detect dark matter using these distorted images of a background quasar and its host galaxy.

Astronomers love to give weird names to things, but “dark matter” is pretty self-explanatory. It’s matter, or we think it is, because it exerts a gravitational pull. It’s also dark, cause we can’t see it (although we observe its effect) — and that’s pretty much all we know about it.

Dark matter is estimated to account for approximately 85% of the matter in the universe, and yet we don’t really know what it is. But a new study might help us in that regard.

As weird as it may sound, dark matter seems to “clump together”. Turns out, these clumps can be much smaller than we thought. This confirms a fundamental prediction about dark matter, and can help researchers make an important breakthrough in understanding this enigmatic phenomenon.

A dark hunt

Dark matter is invisible to all our instruments. It doesn’t emit light or any detectable radiation. We never imaged it in any direct way. So when studying dark matter, astrophysicists look for its effects.

The most prevalent of these effects is its gravitational effect. According to such observations, dark matters appears to be the gravitational “glue” holding galaxies together.

We don’t know what kind of particles dark matter would be made of, but it almost certainly wouldn’t be the electrons, protons, and neutrons we’re familiar with. A popular theory holds that whatever particles it may be made of, these particles wouldn’t move very fast. This would help explain why dark matter tends to clump together, and while the dark matter concentrations across the universe can vary so much.

If this were the case, this would make for “cold” dark matter. A competing theory supports the idea of “hot” dark matter, where particles are moving at relativistic speeds (close to the speed of light).

Clumps of dark matter can help solve this dilemma. “Hot” dark matter wouldn’t allow the formation of small clumps, they simply move too fast to allow small chunks to form. So if we could detect small clumps, this would lend support to the “cold” dark matter hypothesis.

But remember how we said that dark matter can’t be imaged? Yeah, that’s still a problem.

Gravitational lensing

So instead, researchers took to an old tool: gravitational lensing. But they gave it a new twist.

Gravitational lensing, as the name implies, is the technique of using gravitational attraction as a lens. Everything has a gravitational pull, but objects that are really massive can distort even light itself. While this is often a very subtle distortion, it’s still detectable.

Think of it this way: if we’re looking at a distant, bright galaxy through a telescope, and another massive object is interposed between our telescope and the galaxy, its gravitation can act as a lens, bending the light. This is what was done in this study.

Image credits: NASA, ESA, and D. Player/STScI.

As you might have guessed, this requires a very particular alignment — which means that gravitational lenses must be found — and they may not exist in the directions we want them.

But sometimes, ever so rarely, the objects involved are lined up in such a way that four distorted images are produced around the lensing object. This is called an Einstein cross. This is where things get really interesting.

You might be wondering what any of this has to do with dark matter. Well, the gravitational influence of dark matter clumps should be observable — even that of smaller clumps.

The team used the Hubble Space Telescope to study eight Einstein cross quasars — extremely luminous galactic cores powered by supermassive black holes. These quasars were gravitationally lensed by massive foreground galaxies.

“Imagine that each one of these eight galaxies is a giant magnifying glass,” said UCLA astrophysicist Daniel Gilman, one of the study authors.

“Small dark matter clumps act as small cracks on the magnifying glass, altering the brightness and position of the four quasar images compared to what you would expect to see if the glass were smooth.”

The eight quasars and galaxies were aligned so precisely that the warping effect produced four distorted images of each quasar, almost like looking at a carnival mirror. Such alignments are very rare and were fortunate for this study.

The presence of the dark matter clumps altered the apparent brightness and position of each distorted quasar image. The researchers measured how the light was warped by the lens, and then looked at the brightness and position of each of the images, comparing these against predictions of how the Einstein crosses would look without dark matter. These comparisons allowed them to calculate the mass of the dark matter clumps causing the distortion.

According to the results, small dark matter clumps could exist — and these observations support the existence of colder dark matter.

“Dark matter is colder than we knew at smaller scales,” said Anna Nierenberg of NASA’s Jet Propulsion Laboratory in Pasadena, California, leader of the Hubble survey. “Astronomers have carried out other observational tests of dark matter theories before, but ours provides the strongest evidence yet for the presence of small clumps of cold dark matter. By combining the latest theoretical predictions, statistical tools and new Hubble observations, we now have a much more robust result than was previously possible.”

This does not rule out the possibility of hotter dark matter, but lends more weight to the colder theory. To make matters even more complex, there is also a mixed dark matter model that includes both types. However, this is almost certainly not the last study of this type.

Astronomers will be able to conduct follow-up studies of dark matter using future NASA space telescopes such as the James Webb Space Telescope and the Wide Field Infrared Survey Telescope, both infrared observatories.

It’s remarkable that after decades of service, the Hubble telescope still provides extremely useful information, allowing us to understand aspects of the surrounding universe.

As for dark matter, we won’t unravel its secrets today or tomorrow. We’re still taking baby steps, but one at a time, we’re getting closer to understanding what it really is — and maybe then, it won’t be dark matter anymore.

The team will present its results at the 235th meeting of the American Astronomical Society in Honolulu.

A new equation may have finally solved Einstein’s ‘biggest blunder’

Credit: Public Domain.

In 1917, not long after publishing the theory of general relativity, Albert Einstein played some mathematical gymnastics with his field equations — a set of equations that relate the curvature of spacetime to the amount of matter and energy moving through a region of spacetime. At the time, everybody thought that the universe is stationary. For the framework of his theory of general relativity to make any sense under these conditions, Einstein inserted a term called the cosmological constant (denoted by the Greek capital letter lambda).

But almost a decade later, Edwin Hubble proved beyond a doubt that the universe was not static — it was, in fact, expanding. Upon hearing the news, Einstein abandoned the cosmological constant, calling it the “biggest blunder” of his life.

However, this wasn’t the end of it. In 1998, scientists discovered that the universe wasn’t only expanding, it was doing so at an accelerated rate. Some unknown force was overcoming gravity, making galaxies move away from each other increasingly faster. This force is known today as dark energy, and it’s true nature still remains a mystery.

Ironically, physicists had to reintroduce the cosmological constant into Einstein’s field equations in order to account for this new force, which constitutes about 70% of the energy content in the universe. This constant employ a different value than Einstein would have thought, but the idea is still exactly what Einstein came up with.

In the current standard model of cosmology, the cosmological constant estimates its value as 10-52 per square meter — that’s incredibly tiny but over the scale of the universe, this constant becomes significant enough to accelerate the expansion of space.

The cosmological constant also includes “vacuum energy” or “zero point energy” — the energy density of empty space. When physicists try to calculate its contribution to the cosmological constant, they end up with an absurd value in the order of 10 120 (yes, 10 followed by 120 zeroes). The discrepancy between the two proposed values of the cosmological constant is unacceptable, to say the least.

This may mean that Einstein’s original field equations for gravity are wrong — but that is extremely unlikely. The theory of general relativity is one of the most tested frameworks in physics, having stood scrutiny time and time again. The fairly recent detection of gravitational waves by the LIGO experiment suggests that Einstein’s theory is the best we’ve got so far that explains gravity.

Instead of doubting Einstein’s theory of general relativity, Lucas Lombriser, an assistant professor of theoretical physics at the University of Geneva in Switzerland, simply added a new equation on top of the field equations. Essentially, what Lombriser did was to assume that the gravitational constant (the one first used by Isaac Newton in his laws of gravity) can change. Yes, constants have really lost their semantics in modern theoretical physics.

At any rate, the Lombriser version of general relativity assumes that the gravitational constant remains the same within the observable universe but can change beyond it. In other words, his theory assumes that there are multiple universes — that we live in a multiverse — some of which may function with different values for the fundamental constants.

After accounting for the estimated mass of all the galaxies, stars, and dark matter in the universe, Lombriser found that this framework returned a value for the cosmological constant that closely agrees with experimental observations. Specifically, he found the universe is made of 74% dark energy whereas observations estimate 68.5% — a huge improvement, to say, the least over the previous discrepancy.

Unfortunately for Lombriser, who published his work in the journal Physics Letters B, there’s no way to actually test his theory — at least not yet.

What’s shocking. though, if you think about it for a second is that even Einstein’s ‘bad’ ideas were brilliant!

A UA-led team of scientists generated millions of different universes on a supercomputer, each of which obeyed different physical theories for how galaxies should form. (Image: NASA, ESA, and J. Lotz and the HFF Team/STScI)

Researchers simulate millions of virtual universes to study star formation

Researchers have turned to a massive supercomputer — dubbed the ‘UniverseMachine’ — to model the formation of stars and galaxies. In the process, they created a staggering 8 million ‘virtual universes’ with almost 10¹⁴ galaxies.

A UA-led team of scientists generated millions of different universes on a supercomputer, each of which obeyed different physical theories for how galaxies should form. (Image: NASA, ESA, and J. Lotz and the HFF Team/STScI)
A UA-led team of scientists generated millions of different universes on a supercomputer, each of which obeyed different physical theories for how galaxies should form. (Image: NASA, ESA, and J. Lotz and the HFF Team/STScI)

To say that the origins and evolution of galaxies and the stars they host have been an enigma that scientists have sought to explore for decades is the ultimate understatement.

In fact, desire to understand how the stars form and why they cluster the way they do, predates science, religion and possibly civilisation itself. As long as humans could think and reason — way before we knew what either a ‘star’ or a ‘galaxy’ was— we looked to the heavens with a desire to have knowledge of its nature.

We now know more than we ever have, but the heavens and their creation still hold mysteries for us. Observing real galaxies can only provide researchers with a ‘snapshot’ of how they appear at one moment. Time is simply too vast and we exist for far too brief a spell to observe galaxies as they evolve.

Now a team of researchers led by the University of Arizona have turned to supercomputer simulations to bring us closer to an answer for these most ancient of questions.

Astronomers have used such computer simulations for many years to develop and test models of galactic creation and evolution — but it only works for one galaxy at a time — thus failing to provide a more ‘universal’ picture.

To overcome this hurdle, Peter Behroozi, an assistant professor at the UA Steward Observatory, and his team generated millions of different universes on a supercomputer. Each universe was programmed to develop with a separate set of physical theories and parameters.

As such the team developed their own supercomputer — the UniverseMachine, as the researchers call it —to create a virtual ‘multiverse’ of over 8-million universes and at least 9.6 x 10¹³ galaxies.

The results could solve a longstanding quirk of galaxy-formation — why galaxies cease forming new stars when the raw material — hydrogen — is not yet exhausted.

The study seems to show that supermassive black holes, dark matter and supernovas are far less efficient at stemming star-formation than currently theorised.

The team’s findings — published in the journal Monthly Notices of the Royal Astronomical Society — challenges many of the current ideas science holds about galaxy formation. In particular, the results urge a rethink of how galaxies form, how they birth stars and the role of dark matter — the mysterious substance that makes up 80% of the universe’s matter content.

Behroozi, the study’s lead author. says: “On the computer, we can create many different universes and compare them to the actual one, and that lets us infer which rules lead to the one we see.”

What makes the study notable is it is the first time each universe simulated has contained 12 million galaxies, spanning a time period of 400 million years after the ‘big bang’ to the present day. As such, the researchers have succeeded in the creation of self-consistent universes which closely resemble our own.

Putting the multiverse to the test — how the universe is supposed to work

To compare each universe to the actual universe, each was put through a series of tests that evaluated the appearance of the simulated galaxies they host in comparison to those in the real universe.

Common theories of how galaxies form stars involve a complex interplay between cold gas collapsing under the effect of gravity into dense pockets giving rise to stars. As this occurs, other processes are acting to counteract star formation.

The Hubble Space Telescope took this image of Abell 370, a galaxy cluster 4 billion light-years from Earth. Several hundred galaxies are tied together by gravity. The arcs of blue light are distorted images of galaxies far behind the cluster, too faint for Hubble to see directly. (Image: NASA, ESA, and J. Lotz and the HFF Team/STScI)

For example, we believe that most galaxies harbour supermassive black holes in their centres. Matter forming accretion discs around these black holes and eventually being ‘fed’ into them, radiate tremendous energies. As such, these systems act almost as a ‘cosmic blowtorch’ heating gas and preventing it from cooling down enough to collapse into stellar nurseries.

Supernova explosions — the massive eruption of dying stars — also contribute to this process. In addition to this, dark matter provides most of the gravitational force acting on the visible matter in a galaxy — thus, pulling in cold gas from the galaxy’s surroundings and heating it up in the process.

Behroozi elaborates: “As we go back earlier and earlier in the universe, we would expect the dark matter to be denser, and therefore the gas to be getting hotter and hotter.

“This is bad for star formation, so we had thought that many galaxies in the early universe should have stopped forming stars a long time ago.”

But what the team found was the opposite.

Behroozi says: “Galaxies of a given size were more likely to form stars at a higher rate, contrary to the expectation.”

Bending the rules with bizarro universes

In order to match observations of actual galaxies, the team had to create virtual universes in which the opposite was the case — universes in which galaxies continued to birth stars for much longer.

Had the researchers created universes based on current theories of galaxy formation — universes in which the galaxies stopped forming stars early on — those galaxies appeared much redder than the galaxies we see in the sky.

Ancient galaxies such as z8_GND_5296 appear red for two reasons; the lack of young blue stars and the stretching in the wavelength of emitted light due to cosmic redshift. (V. Tilvi, Texas A&M University/S.L. Finkelstein, University of Texas at Austin/C. Papovich, Texas A&M University/CANDELS Team and Hubble Space Telescope/NASA)
Ancient galaxies such as z8_GND_5296 appear red for two reasons; the lack of young blue stars and the stretching in the wavelength of emitted light due to cosmic redshift. (V. Tilvi, Texas A&M University/S.L. Finkelstein, University of Texas at Austin/C. Papovich, Texas A&M University/CANDELS Team and Hubble Space Telescope/NASA)

Galaxies appear red for major two reasons. If the galaxy formed earlier in the history of the universe cosmic expansion — the Hubble flow — means that it will be moving away from us more rapidly, causing significant elongation in the wavelength of the light it emits shifting it to the red end of the electromagnetic spectrum. A process referred to as redshift.

In addition to this, another reason an older galaxy may appear red is intrinsic to that galaxy and not an outside effect like redshift. If a galaxy has stopped forming stars, it will contain fewer blue stars, which typically die out sooner, and therefore be left with older — redder — stars.

Behroozi point out that isn’t what the team saw in their simulations, however. He says: “If galaxies behaved as we thought and stopped forming stars earlier, our actual universe would be coloured all wrong.

“In other words, we are forced to conclude that galaxies formed stars more efficiently in the early times than we thought. And what this tells us is that the energy created by supermassive black holes and exploding stars is less efficient at stifling star formation than our theories predicted.”

Computing the multiverse is as difficult as it sounds

Creating mock universes of unprecedented complexity required an entirely new approach that was not limited by computing power and memory, and provided enough resolution to span the scales from the “small” — individual objects such as supernovae — to a sizeable chunk of the observable universe.

Behroozi explains the computing challenge the team had to overcome: “Simulating a single galaxy requires 10 to the 48th computing operations. All computers on Earth combined could not do this in a hundred years. So to just simulate a single galaxy, let alone 12 million, we had to do this differently.”

In addition to utilizing computing resources at NASA Ames Research Center and the Leibniz-Rechenzentrum in Garching, Germany, the team used the Ocelote supercomputer at the UA High-Performance Computing cluster.

Two-thousand processors crunched the data simultaneously over three weeks. Over the course of the research project, Behroozi and his colleagues generated more than 8 million universes.

He explains: “We took the past 20 years of astronomical observations and compared them to the millions of mock universes we generated.

“We pieced together thousands of pieces of information to see which ones matched. Did the universe we created look right? If not, we’d go back and make modifications, and check again.”

Behroozi and his colleagues now plan to expand the Universe Machine to include the morphology of individual galaxies and how their shapes evolve over time.

As such they stand to deepen our understanding of how the galaxies, stars and eventually, life came to be.


Original research:https://academic.oup.com/mnras/article/488/3/3143/5484868

Ancient galaxies from the study are visible to ALMA (right) but not to Hubble (left). Credit: © 2019 Wang et al.

‘Hidden’ ancient galaxies discovery may redefine our understanding of the Universe

The discovery of 39 ‘hidden’ ancient galaxies urges scientists to rethink their theories of fundamental aspects of the Universe — including supermassive black holes, star formation rates, and the ever-elusive, dark matter.

Ancient galaxies from the study are visible to ALMA (right) but not to Hubble (left). Credit: © 2019 Wang et al.

In an unprecedented discovery of astronomers, researchers have utilised the combined power of a multitude of observatories across the globe to discover a vast array of 39 previously hidden galaxies.

The finding — described by the researchers from the University of Tokyo as a ‘treasure trove’ — is the first multiple discoveries of this kind. But the finding is significant for more than its size alone.

In addition to containing a wealth of newly discovered ancient galaxies, an abundance of this particular type of galaxy suggests that scientists may have to refine current models of the universe.

This is because our current understanding of the universe and how it formed is built upon observations of galaxies in ultraviolet light. But observations in these wavelengths under-represent the most massive galaxies — those with high dust content and crucially, the most ancient.

This means that a discovery of such galaxies — such as the one just made — must force us to reconsider the rates of star formation in the early universe. The study explains that the population of stars discovered may mean that star formation rates were actually ten times greater in early epochs than previous estimates held.

There are also particular ramifications for our understanding of both supermassive black holes and their distribution, and for the concept of dark matter — the elusive substance which makes up 80% of the matter in the universe.

Despite the wealth of astronomical data that has become available to scientists since the launch of the Hubble Space Telescope, researchers at the Institute of Astronomy in Toyko were aware there were things that Hubble simply couldn’t show us. It was these things — fundamental pieces of the cosmic puzzle — that they wanted to investigate.

They achieved this by unifying different observatories, using them to look more deeply in the Universe than Hubble alone could do. This is what led them to this huge collection of galaxies.

Researcher Tao Wang describes the uniqueness and magnitude of the team’s discovery: “This is the first time that such a large population of massive galaxies was confirmed during the first two billion years of the 13.7-billion-year life of the universe.

“These were previously invisible to us.”

Wang continues: “This finding contravenes current models for that period of cosmic evolution and will help to add some details, which have been missing until now.”

A different view of the universe

Wang explains that if we could see these galaxies and the light they shed, our view from the Milky way would be significantly different: “For one thing, the night sky would appear far more majestic. The greater density of stars means there would be many more stars close by appearing larger and brighter.

“But conversely, the large amount of dust means farther-away stars would be far less visible, so the background to these bright close stars might be a vast dark void.”

The galaxies have been difficult to see from Earth due to how faint they are. Were we able to see these stars, their density would make the night sky majestic, Wang says.

The light from these galaxies also has to battle extinction — the absorption of light) by intervening interstellar dust clouds. The light from the galaxies also has to travel great distances meaning the wavelength is redshifted by the expansion of the universe making it even less visible.

Professor Kotaro Kohno. Credit: © 2019 Rohan Mehra — Division of Strategic Public Relations

Professor Kotaro Kohno explains that this phenomenon is how the galaxies escaped Hubble’s gaze: “The light from these galaxies is very faint with long wavelengths invisible to our eyes and undetectable by Hubble.

“So we turned to the Atacama Large Millimeter/submillimeter Array (ALMA), which is ideal for viewing these kinds of things. I have a long history with that facility and so knew it would deliver good results.”

This redshift due to cosmic expansion does have its advantages, however. It allows astronomers to estimate not just the distances to the galaxies in question, but it also allows them to calculate just how long ago the light was emitted.

The hidden implications of these hidden galaxies

The team’s finding is so controversial and poses such a radical rethink that they found their fellow astronomers were initially reluctant to believe they had found what they claimed.

A few of the 66 radio telescope antennas that make up ALMA. Credit: © 2019 Kohno et al.

Wang explains: “It was tough to convince our peers these galaxies were as old as we suspected them to be. Our initial suspicions about their existence came from the Spitzer Space Telescope’s infrared data.

“But ALMA has sharp eyes and revealed details at submillimeter wavelengths, the best wavelength to peer through dust present in the early universe. Even so, it took further data from the imaginatively named Very Large Telescope in Chile to really prove we were seeing ancient massive galaxies where none had been seen before.”

The discovery has the potential to reshape our ideas of the supermassive black holes that scientists currently believe nestle at the centre of most galaxies.

Kohno elaborates: “The more massive a galaxy, the more massive the supermassive black hole at its heart.

“So the study of these galaxies and their evolution will tell us more about the evolution of supermassive black holes, too.”

Kohno also explains that some ideas regarding dark matter may have to be revised, too: “Massive galaxies are also intimately connected with the distribution of invisible dark matter. This plays a role in shaping the structure and distribution of galaxies. Theoretical researchers will need to update their theories now.”

In addition to the potential shake up the team believes that their findings may already present, they expect more surprises to come.

Wang concludes: These gargantuan galaxies are invisible in optical wavelengths so it’s extremely hard to do spectroscopy, a way to investigate stellar populations and chemical composition of galaxies. ALMA is not good at this and we need something more.

“I’m eager for upcoming observatories like the space-based James Webb Space Telescope to show us what these primordial beasts are really made of.”


Original research: T. Wang, C. Schreiber, D. Elbaz, Y. Yoshimura, K. Kohno, X. Shu, Y. Yamaguchi, M. Pannella, M. Franco, J. Huang, C.F. Lim & W.H. Wang. A dominant population of optically invisible massive galaxies in the early Universe. Nature. DOI: 10.1038/s41586–019–1452–4

*Something* is blasting “cosmic bullet holes” through our galaxy

We don’t know what it is. We don’t even know if it’s made of regular matter — but we do know that something blasted a series of holes through some stars in the Milky Way.

“It’s a dense bullet of something,” said Ana Bonaca, a researcher at the Harvard-Smithsonian Center for Astrophysics, who discovered evidence of the impactor.

Bonaca analyzed a series of stars called GD-1 — a very long, thin, Milky Way star stream. GD-1 stars have been studied ever since they were discovered in 2006, and Bonaca has been using data from the recently launched Gaia telescope to analyze them in more detail, finding something bizarre smack in the middle of the stream.

This type of stellar stream is created by the tidal (gravitational) force of the Milky Way, which bends and stretches the stream, producing a gap about midway through the stream.

But when Bonaca looked at GD-1 more recently, she found a second gap — and a weird one at that. The second gap is not smooth as the first one but has a ragged edge — as if something was shot through it.

“It’s a dense bullet of something,” Bonaca said.

The “bullet” would have to be something absolutely massive, much bigger than a star, and more massive than all but the largest of black holes. It’s not out of the question for a supermassive black hole to be the culprit, but if this is the case, it would have to be one at the scale of the supermassive black hole at the center of our galaxy. There isn’t a clear reason why such a black hole would exist towards the edge of our galaxy, and astronomers haven’t seen any effects from it.

This leaves another tantalizing possibility: a massive object made of dark matter.

Dark matter is a hypothetical form of matter that is thought to account for approximately 85% of the matter in the universe and about a quarter of its total energy density. We don’t know what dark matter is and we’ve never seen it — but we have seen its effects, and astronomers are quite confident that it exists. We also have no idea how dark matter might be distributed through the universe — is it thin and diffusive, or large and clumpy? If dark matter was indeed shot through GD-1 stars, it would suggest the latter. However, a large ball of dark matter is still speculative at this point, although it seems to line up with the evidence quite nicely.

The results have not yet been peer-reviewed, though they were met positively at the conference of the American Physical Society in Denver where they were presented.

At this point, the turbulent history of GD-1 stars just isn’t established well enough to draw a definite conclusion. But whatever it is, is Bonaca’s hypothesis is true, something shot a massive “bullet” straight through our galaxy — and we don’t know what it is.

Abell S1063, a galaxy cluster, was observed by the NASA/ESA Hubble Space Telescope as part of the Frontier Fields programme. The huge mass of the cluster — containing both baryonic matter and dark matter — acts as cosmic magnification glass and deforms objects behind it. In the past astronomers used this gravitational lensing effect to calculate the distribution of dark matter in galaxy clusters. Credit: NASA, ESA, and M. Montes (University of New South Wales, Sydney, Australia).

Astronomers find a new way to ‘see’ dark matter using starlight from rogue stars

Abell S1063, a galaxy cluster, was observed by the NASA/ESA Hubble Space Telescope as part of the Frontier Fields programme. The huge mass of the cluster — containing both baryonic matter and dark matter — acts as cosmic magnification glass and deforms objects behind it. In the past astronomers used this gravitational lensing effect to calculate the distribution of dark matter in galaxy clusters. Credit: NASA, ESA, and M. Montes (University of New South Wales, Sydney, Australia).

Abell S1063, a galaxy cluster, was observed by the NASA/ESA Hubble Space Telescope as part of the Frontier Fields programme. The cluster — containing both baryonic matter and dark matter — acts as a cosmic magnifying glass and deforms objects behind it. In the past, astronomers used this gravitational lensing effect to calculate the distribution of dark matter in galaxy clusters. Credit: NASA, ESA, and M. Montes (University of New South Wales, Sydney, Australia).

Some stars have no galactic allegiance. These rogue stars, which are not gravitationally bound to any galaxy, roam freely throughout intergalactic space. Now, astronomers claim that starlight emitted by rogue stars could be used to map the distribution of dark matter in the universe.

Dark matter and dark energy make up 95% of the observable universe, despite the fact that none of our instruments are capable of detecting them. Yet scientists know that dark matter must exist because of the gravitational force it exerts on the surrounding matter — and whose effects we can measure. For instance, dark energy is the only thing that explains the acceleration of the expansion of the universe, which has been thoroughly documented.

Scientists have used all sorts of methods to plot the distribution of dark matter in the universe. One of the most widely-used methods exploits the fact that dark matter bends the light around it, altering its movement. This phenomenon, known as gravitational lensing, can be measured. Previously, this method was successfully used to create a 3D map of dark matter based on observations of 10 million galaxies, including those from very far away in space, from which light created billions of years ago is only now reaching Earth.

Now, scientists have a new trick that reveals the presence of dark matter — and it works by studying the starlight of rogue stars. When two galaxies interact, individuals stars can be stripped apart from their galactic homes, left free to roam within the cluster. These stars end up vagabonding where the majority of the mass of the cluster resides, which is mostly made of dark matter. So by pinpointing the source of rogue starlight, the astronomers claim that they can map dark matter.

“We have found a way to ‘see’ dark matter,” Mireia Montes, of the University of New South Wales, Australia, and lead author of the study, said in a statement. “We have found that very faint light in galaxy clusters, the intracluster light, maps how dark matter is distributed.”

According to Montes, intracluster light is aligned with dark matter, tracing its distribution more accurately than any other method relying on light used so far. The method is also more efficient than those based on gravitational lensing, which requires complex and time-consuming spectroscopy.

All that we know for sure right now is that dark matter seems to interact with regular matter gravitationally. But if scientists find that dark matter is distributed significantly different than light from free-floating stars, that could be a game changer. Ultimately, work such as this might one-day probe the fundamental nature of dark matter.

“If dark matter is self-interacting we could detect this as tiny departures in the dark matter distribution compared to this very faint stellar glow,” highlighted Ignacio Trujillo, of the Instituto de Astrofísica de Canarias, Spain, co-author of the study.

The findings appeared in the Monthly Notices of the Royal Astronomical Society.

Map of dark matter in region G12 of the sky. Credit: KiDS survey.

Oxford scientist may have finally solved dark matter riddle — the universe might be made out of a ‘negative mass’ fluid

Map of dark matter in region G12 of the sky. Credit: KiDS survey.

Map of dark matter in region G12 of the sky. Credit: KiDS survey.

Dark matter and dark energy make up 95% of the observable universe despite the fact that none of our instruments are capable of detecting it. What’s up with that? Scientists would sure like to know as well, although that doesn’t mean they’re completely in the dark. According to one of the most exciting researches on dark matter to date, this elusive form of matter may combine with dark energy to form a fluid with ‘negative mass’.

What does negative mass even mean, you might ask? It’s another a weird thing that physicists have constructed in order to explain even weirder phenomena. A hypothetical type of matter with negative mass would also have negative gravity, which means it would repel other matter around it. Likewise, if you’d push an object with negative mass, it would accelerate towards you.

Just like normal matter, negative mass would become spread out as the universe expands. But our observations suggest that dark energy does not thin out over time, which means it shouldn’t be negative mass. For this reason, many cosmologists have abandoned the idea of associating negative mass with dark energy.

Dr. Jamie Farnes from the University of Oxford is of a different opinion. The scientist has proposed a modification to Einstein’s theory of general relativity that allows negative masses to not only exist, but to be created continuously. This way, both dark matter and dark energy can be unified into a single fluid. When more and more negative mass is being added, the fluid does not dilute during the expansion of the universe.

“We now think that both dark matter and dark energy can be unified into a fluid which possesses a type of ‘negative gravity,” repelling all other material around them. Although this matter is peculiar to us, it suggests that our cosmos is symmetrical in both positive and negative qualities,” Dr. Farnes said in a statement.

Farnes seems to be on to something. His work is not some purely theoretical work either. For instance, the model can predict the observed behavior of dark matter halos — the invisible fabric that keeps galaxies from tearing themselves apart. The video below shows a simulation created by Farnes which predicts how dark matter halos form with properties just like the ones inferred from observations by modern radio telescopes.

What’s more, negative mass isn’t purely theoretical either. Air bubbles in water can be modeled to have negative mass and, quite recently, scientists were able to generate particles that behave exactly as they would if they had negative mass.

[panel style=”panel-info” title=”Dark matter and dark energy” footer=””]Dark matter cannot be detected by our instruments, i.e. it’s completely invisible. Yet scientists know that it must exist because of the gravitational force it exerts on the surrounding matter that we can measure. Dark energy is the repulsive force that is responsible for the expansion of the universe at an accelerating rate.

Until now, the two have been treated separately. Now, Dr. Farnes claims that both are part of the same phenomenon — a unified dark fluid of negative mass. [/panel]

Albert Einstein actually provided  the first hint of a dark universe 100 years ago when he introduced a parameter in his equations known as ‘cosmological constant.’ Today, this parameter has become synonymous with dark energy, but Einstein always thought that it represents a failure on his behalf. In some of his notes, Einstein stated that ‘a modification of the theory is required such that “empty space” takes the role of gravitating negative masses which are distributed all over the interstellar space.” So, one might say that Einstein was the first to predict a negative-mass-filled universe.

“Previous approaches to combining dark energy and dark matter have attempted to modify Einstein’s theory of general relativity, which has turned out to be incredibly challenging. This new approach takes two old ideas that are known to be compatible with Einstein’s theory—negative masses and matter creation—and combines them together,” Dr. Farnes said.

“The outcome seems rather beautiful: dark energy and dark matter can be unified into a single substance, with both effects being simply explainable as positive mass matter surfing on a sea of negative masses.”

The new study might help solve some dicey problems in String Theory, which hopes to unify quantum physics with general relativity, but which is also plagued by inconsistencies with observational evidence. One of the tenets of string theory is that energy in empty space must be negative, which fits beautifully with the idea of a negative mass dark fluid. What’s more, a dark fluid could also explain why the Hubble constant — the relationship between the speed and the distance of a galaxy — seems to vary. A negative mass cosmology actually predicts that the Hubble constant should vary, which wouldn’t make it a constant at all, obviously.

Dr. Farnes’ theory will be tested with more scrutiny by the Square Kilometre Array (SKA), the world’s largest telescope. SKA’s main goal will be to measure the distribution of galaxies throughout the history of the universe

“If real, it would suggest that the missing 95% of the cosmos had an aesthetic solution: we had forgotten to include a simple minus sign,” the scientist concluded.

Scientific reference: J. S. Farnes. A unifying theory of dark energy and dark matter: Negative masses and matter creation within a modified LambdaCDM framework, Astronomy & Astrophysics (2018). DOI: 10.1051/0004-6361/201832898 , https://arxiv.org/abs/1712.07962

Credit: C. O'Hare; NASA/Jon Lomberg.

The Earth is smack in the middle of a ‘dark matter hurricane’

According to an international team of astronomers, our solar system is in the path of a “dark matter hurricane” — but there’s no need to panic. The whole event is totally harmless and, what’s more, might actually help scientists finally detect this elusive phenomenon.

Credit: C. O'Hare; NASA/Jon Lomberg.

Credit: C. O’Hare; NASA/Jon Lomberg.

Dark matter makes up roughly 27% of the universe, whereas “regular” matter accounts for only 5% — the rest being accounted for by dark energy. despite its ubiquity, nobody knows what dark matter really is or how it works. At the same time, nothing other than dark matter can explain the motion of stars and galaxies, which are expanding more than can be accounted for by regular, visible matter.

Although the evidence for the existence of dark matter is very strong, identifying it has proven extremely challenging — but we may now have a good shot. Researchers from Universidad de Zaragoza, King’s College London and the Institute of Astronomy in the U.K. have been studying a stellar stream left behind by a dwarf spheroidal galaxy that was devoured by the Milky Way aeons ago. The S1 stream, as it was called, was discovered just last year by a team studying data from the Gaia satellite.

Other such streams have been observed before, but this is the first to cross paths with our own solar system. Luckily, none of the 30,000 stars that comprise S1 will collide with us. However, the dark matter that’s moving along with this stream might be picked up by detectors on Earth.

According to several models showing the distribution of the dark matter and its density, the dark matter hurricane is traveling at a staggering 500 km/s. The analysis also allowed the researchers to predict which possible signatures of the stream scientists ought to look for to find dark matter. For instance, the results suggest that WIMP detectors have a slim chance of picking up anything. Weakly interacting massive particles (WIMPs) are hypothetical particles that are thought to constitute dark matter and, by virtue of their weak-scale interaction, WIMPs should be able to be observed by directly detecting their interactions with ordinary matter.

On the other hand, axion detectors may actually have a fighting chance, the authors write in the journal Physical Review DAxions are hypothetical particles that have a small mass in the milli-electronvolt (eV) range, making them 500 million times lighter than an electron. Additionally, an axion should have no spin. Detectors such as the Axion Dark Matter Experiment might be able to pickup axions from S1 due to possible bumps in the broad spectrum of axions. In the presence of a strong magnetic field, axions should be converted into photons, which we can see, according to a previous estimate.

While there are over 30 such streams known in our galaxy, S1 is the only one to directly interact with our solar system. What’s more, our paths will intersect for millions of more years. So, even if our technology is not advanced enough to detect dark matter particles, there is still plenty of time for more sensitive detectors to be built.

Scientists measure physical constant in unprecedented detail, which may reveal exotic physics

Researchers have measured the Fine-Structure Constant with the utmost precision. In doing so, they’ve come up with evidence that might tell us what dark particles and forces might or might not lurk beyond the Standard Model. 

Credit: Pixabay.

The Fine-Structure Constant represents the strength of the electromagnetic force that controls how charged elementary particles (such as electrons and photons) interact.

Up until now, determining the Fine-Structure Constant has mostly fallen in the realm of theory, with scientists using the magnetic properties of electrons to derive its value. Now, a team of researchers at the University of California and Lawrence Berkeley National Laboratory have finally managed to measure the constant through more direct means.

The physicists fired a laser at cesium-133 atoms to force them into a quantum superposition, and then studied what happened to the atoms ‘relax’ back into their natural state. The laser basically guided the atoms along certain paths, producing an interference that is intensely sensitive to the interactions between the lasers’ photons and the atoms. Because the strength of this interaction is governed by the Fine-Structure Constant, the researchers could deduce the speed at which the atoms traveled when they were struck by the laser — ultimately, this led to a new measurement of the constant to better than one part per billion, a three-fold reduction in the error compared to previous work.

The new value closely matched the theoretical one, confirming theories that suggest electrons aren’t made of smaller, unknown particles. At the same time, it deepens a mystery concerning so-called dark photons. These elusive particles should be, as the theory goes, nearly identical to photons, except in one particular aspect: they have mass that would allow them to interact with other particles. Dark matter theory, in general, favors the existence of dark photons, which are thought to be force carriers.

But that’s not to say that these experiments are the last word on these Standard Model extensions. The results may be wrong in the first place, for instance. Additionally, the value calculated by the researchers was close to that theorized but not exact, so there is still room for other particle theories to explain the discrepancy. On the bright side, the method employed by this study provides a new, standardized way to measure the absolute mass of atoms, which means we’ll be able to one day standardize the kilogram — the fundamental unit of mass — without having to rely on some dead weight. 

Richard H. Parker et al. Measurement of the fine-structure constant as a test of the Standard Model, Science (2018). DOI: 10.1126/science.aap7706. 

Dark matter may be a manifestation of extremely advanced alien life, researchers suggest

Our limited understanding of dark matter and the fact that we’re focusing on the wrong things might be preventing us from discovering alien life.

This collage shows NASA/ESA Hubble Space Telescope images of six different galaxy clusters, with the distribution of dark matter colored in blue.

A Cosmic Gorilla

You know that experiment where you’re supposed to count the number of basketball passes, and you’re so focused on the ball that you don’t even see a bear moving through the picture? Researchers believe something similar might be happening on a cosmic scale. We’re so focused on one thing that we’re completely missing the other — and in this case, ‘the other’ might mean alien signals.

Writing in the journal Acta Astronautica, neuropsychologists Gabriel de la Torre and Manuel García, from the University of Cádiz, say that when it comes to detecting alien signals, we might be looking in the wrong direction. They say that we’re looking for aliens that act similarly to us when that might really not be the case.

“When we think of other intelligent beings, we tend to see them from our perceptive and conscience sieve; however we are limited by our sui generis vision of the world, and it’s hard for us to admit it,” says De la Torre, who prefers to avoid the terms ‘extraterrestrial’ or aliens by its Hollywood connotations and uses more generic terms, such as ‘non-terrestrial’.

“What we are trying to do with this differentiation is to contemplate other possibilities,” he says “for example, beings of dimensions that our mind cannot grasp; or intelligences based on dark matter or energy forms, which make up almost 95% of the universe and which we are only beginning to glimpse. There is even the possibility that other universes exist, as the texts of Stephen Hawking and other scientists indicate.”

The awareness test that inspired the study. Try to count the number of basketball passes. Did you also catch something out of the ordinary?

Hardwired to miss it

In order to test their hypothesis, they had 137 people distinguish aerial photographs with artificial structures (such as buildings or roads) from others with natural elements (such as mountains or rivers). In one of the images, a tiny character disguised as a gorilla was inserted to see if the participants noticed. As expected, participants tended to miss the gorilla. It’s normal because we’re hardwired to miss it — we’re looking for something else. Similarly, if we’re looking for a specific kind of signal, we might completely miss an unrelated type of signal, one we weren’t expecting.

“If we transfer this to the problem of searching for other non-terrestrial intelligences, the question arises about whether our current strategy may result in us not perceiving the gorilla,” stresses the researcher, who insists: “Our traditional conception of space is limited by our brain, and we may have the signs above and be unable to see them. Maybe we’re not looking in the right direction.”

In another example presented in the article, researchers showed participants an apparently geometric structure that can be seen in the images of Occator — an impact crater of the dwarf planet Ceres, famous for its bright spots. Inside the crater appears a strange structure, looking like a square inside a triangle. The point researchers were trying to make is that we sometimes see patterns that just aren’t there, due to the way our brains are wired.

“Our structured mind tells us that this structure looks like a triangle with a square inside, something that theoretically is not possible in Ceres,” says De la Torre, “but maybe we are seeing things where there are none, what in psychology is called pareidolia.”

Image Credits: NASA / JPL-CaltechClose

But the opposite might also be happening, they say. We might have the signal right in front of our eyes, and simply miss it — kind of like a cosmic gorilla effect.

Types of civilizations

We’re not really sure what to expect in terms of potentially advanced alien species, but the most commonly used scale is the Kardashev scale, proposed by Russian astrophysicist Nikolai Kardashev. The scale has three main categories, and it focuses on different stages of energy capture and use, which seems to be a vital requirement for an advanced species:

  • A Type I civilization (a planetary civilization) can use and store all of the energy which reaches its planet from the parent star.
  • A Type II civilization (a stellar civilization) can harness the total energy of its planet’s parent star and use it on a planet.
  • A Type III civilization (a galactic civilization) can control energy on the scale of its entire host galaxy.

If you’ll look at it closely, you’ll see that humans aren’t really even on a Type I level yet, so the Kardashev scale has been extended, both upwards and downwards, including:

  • A Type 0 civilization (humans) that harvests a significant part of its planet energy, just not yet to its full potential.
  • A Type IV civilization (a universal civilization) that can control energy on the scale of the entire universe. This is already a virtually indestructible civilization. This hypothetical civilization would be able to interact with and harvest dark matter and dark energy.
  • A type V civilization (a multiversal civilization) — this already steps into the realm of metaphysics and assumes there is more than one universe, and a civilization that’s able to span and populate several universes.
  • A type VI civilization (deities) that would have the ability to interact with universes outside of time and space, similar in concept to an absolute deity.

Already, it’s becoming quite clear that we don’t even know how to understand very advanced alien civilizations, assuming that they exist. We might be able to understand a Type 0, I, or II civilization, assuming that they do share some similarities with us. But should we come across the higher levels of civilization, would we even realize what we’re looking at? This is what de la Torre and Garcia are asking. For all we know, dark matter and dark energy might hold the traces of such an advanced civilization. Of course, the researchers themselves admit the inherent shortcomings when you’re classifying something you know nothing about.

“We were well aware that the existing classifications are too simplistic and are generally only based on the energy aspect. The fact that we use radio signals does not necessarily mean that other civilizations also use them, or that the use of energy resources and their dependence are the same as we have,” the researchers point out, recalling the theoretical nature of their proposals.

The duo also proposes a different civilization scale, with 3 types. Type 1 is essentially ours, ephemeral, vulnerable to a planetary cataclysm, either natural or self-made. Type 2 is characterized by the longevity of its members, able to explore galaxies and overall much more durable. Type 3, as you’d expect, would be constituted by exotic creatures with eternal or near-eternal life, with an absolute dominion over the universe.

Naturally, this is all a bit speculative. We don’t really know whether we’re looking for the right thing or not, we don’t even know if there is a right thing or not. How likely are we to miss an alien signal, in the case that it exists? Impossible to tell right now. So this study definitely goes a bit ‘out there’, but it poses some intriguing questions.

If anything, the main takeaway is that we should perhaps take a step back and reconsider what alien life might look like. In other words, we shouldn’t only be counting the passes — we should keep an eye out for any gorillas.

Journal Reference: Gabriel G. De la Torre, Manuel A. Garcia. The cosmic gorilla effect or the problem of undetected non terrestrial intelligent signals. Acta Astronautica, 2018; 146: 83 DOI: 10.1016/j.actaastro.2018.02.036

LS1 is the the farthest individual star scientists have ever witnessed. Right panels: region of the sky from 2011 when LS1 wasn't visible and the same patch in 2016 when gravitational lensing enabled observation. Credit: P. Kelly, University of Minnesota/NASA/ESA.

Astronomers find the most distant star ever, looking through a galactic magnifying glass

A stroke of good fortune allowed astronomers to image a bright dot located a staggering 9 billion light-years away. This is the farthest star scientists have ever identified — more than 100 times more distant than any other lone star previously detected. Amazingly, the light we’re currently picking up first shot from the surface of the star ‘only’ 4.4 billion years after the Big Bang.

LS1 is the the farthest individual star scientists have ever witnessed. Right panels: region of the sky from 2011 when LS1 wasn't visible and the same patch in 2016 when gravitational lensing enabled observation. Credit: P. Kelly, University of Minnesota/NASA/ESA.

LS1 is the farthest individual star scientists have ever witnessed. Right panels: region of the sky from 2011 when LS1 wasn’t visible and the same patch in 2016 when gravitational lensing enabled observation. Credit: P. Kelly, University of Minnesota/NASA/ESA.

Typically, when astronomers image cosmic objects attsite:Zmescience.com  such distances, they are very bright bodies like supernovae or galaxy clusters. How could a single, puny star shine as bright as a supernova (the most powerful explosions in the universe)? We just got very lucky — that’s all.

Thanks to a fortuitous cosmic alignment that enabled gravitational lensing, the star in question, called MACS J1149+2223 Lensed Star 1 (LS1), was magnified by a factor of 2,000. Famed physicist Albert Einstein predicted, as a result of his Theory of General Relativity, that whenever light from a distant star passes by a closer object, gravity acts like a magnifying lens bending the distant starlight but also brightening it. This effect has been documented extensively around very massive structures such as galaxies.

Initially, Patrick L. Kelly, an astrophysicist at the University of Minnesota, and colleagues were studying a supernova explosion in the galaxy cluster MACS J1149.5-223 when they picked up a strange blip that appeared in the same galaxy as the supernova. Since this first episode in April 2016, the astronomers were able to use the Hubble Space Telescope to image the hot blue star, which was magnified by a massive cluster of galaxies — the lens of the magnifying glass.

According to spectral measurements, LS1 is an extremely luminous and blue B-type supergiant star, whose surface temperature sits between 11,000 and 14,000 degrees Celsius. That’s more than twice as hot as the sun’s surface.

The astronomers were very lucky that the hot star passed right along the critical curve of the cluster, warping the starlight in our direction and enabling observations at unprecedented distances for a lone star. This effect is like a natural telescope, more powerful than anything we could ever build, according to Kelly.

LS1 will help scientists gain new insights into the constituents of the galaxy cluster. So far, Kelly’s team thinks the microlensing was caused by either a star, a neutron star, or a stellar-mass black hole. Learning about the constituents of galaxy clusters — some of the largest and most massive structures in the universe — will consolidate the science that studies the composition and evolution of the universe. And, as is often the case with such research, dark matter is always lurking.

“If dark matter is at least partially made up of comparatively low-mass black holes, as it was recently proposed, we should be able to see this in the light curve of LS1. Our observations do not favour the possibility that a high fraction of dark matter is made of these primordial black holes with about 30 times the mass of the Sun”, highlights Kelly.

Whatever the case may be, it’s quite amazing to look back in time at three-quarters of the universe’s age — all thanks to starlight and weird physics. In the future, coupling the same gravitational lensing technique with a far more powerful space telescope than Hubble — the upcoming James Webb Telescope — should allow scientists to peer ever further back in time.

The findings appeared in the journal Nature Astronomy.

Astronomers use gravity to zoom in on incredibly distant star

Scientists have used a “cosmic magnifying glass” to image two twinkling stars, billions of light years away, magnifying them over 2,000 times, revealing a lot about the surrounding dark matter in the process.

Image of Icarus (MACS J1149+2223 Lensed Star 1)
Credit: NASA, ESA, and P. Kelly (University of Minnesota).

When you’re studying stars millions and billions of light years away, you need all the help you can get — thankfully, the universe sometimes lends an unexpected hand. This unexpected hand comes in the form of gravity.

In the simplest of terms, astronomers can use clusters of massive galaxies as a lens, to zoom in on some areas of space.  According to general relativity, light follows the curvature of spacetime. Consequently, when light passes around a massive object, it bends. This means that the light from an object on the other side will bend towards an observer’s eye, just like with an ordinary lens. But unlike an optical lens, a gravitational lens has no single focal point, but a focal line.

If it all sounds complex, well, it is — but it’s already a rather common technique in astronomy.

Gravitational lensing can happen on all scales, but it’s especially effective at extremely large scales. Everything bends light (even our own bodies, by an incredibly small amount), but the gravitational field galaxies and clusters of galaxies can lens light enough by observable amounts. In two recent studies, two teams of authors repeatedly observed parts of the sky that contain massive clusters of galaxies, using the Hubble telescope.

In the two studies, researchers report ‘twinkling’ stars. There are several reasons why stars twinkle — which actually means they change brightness abruptly. For instance, they can undergo explosive events (such as a supernova eruption) — and in one case, this was actually the case. But in the other case, the twinkle wasn’t from the star itself — it was due to the relative motion between the lensed star and the lensing cluster, which made the light seem to turn brighter and then dimmer.

By studying these twinkles, researchers can not only infer the physical properties of the star themselves — but also study the distribution of dark matter around them. Dark matter is a type of matter that may constitute about 80% of the total matter in the universe, but we don’t really know that much about it because we can’t study it directly — so far, we’ve only noticed its gravitational effects.

Journal Reference:

In a galaxy far, far away, Dark Matter appears to be missing

Astronomers have discovered a unique galaxy, from which dark matter appears to be completely missing.

We don’t really know what dark matter is and why it exists… or why it doesn’t. Image credits: NASA.

Dark matter, as the name implies, is a pretty mysterious thing. It appears to be an essential part of the universe, and yet we can’t observe it directly — we can only study its effects. Apart from gravity, dark matter doesn’t seem to interact in any way with regular matter, and physicists believe it comprises some kinds of elementary particles that have not yet been discovered

According to the latest astronomical models, dark matter appears to be ubiquitous, accounting for 26.8% of the mass of the universe (matter as we know it only accounts for 4.9%, and the rest 68.3% comes from dark energy — but let’s not get into that now). Despite it being so elusive, its effects have been identified through several different methods, and there is very strong evidence to suggest that dark matter does exist. Most astronomers take it as a given.

Not all galaxies are made the same when it comes to dark matter. For instance, dwarf galaxies have 400 times more dark matter than regular matter, whereas a galaxy like the Milky Way has about 30 times less. But this is the first time a galaxy that appears to have no dark matter was ever discovered.

This Hubble Space Telescope imaging of NGC1052–DF2 was obtained 2016 November 10, using the Advanced Camera for Surveys (ACS). Credits: van Dokkum.

This discovery is so bizarre that researchers aren’t really sure what to make of it. In an email to ZME Science, lead author Pieter van Dokkum explained that there are a few ideas as to how this type of galaxy might come to be, but none of them can truly explain things satisfactorily, and they’re not sure how to interpret this discovery.

“There are ideas out there for forming a dark matter-less galaxy, but none of them fit this particular object very well. For example, it could be that gas was pulled out of a big galaxy in a merger with another galaxy. That gas can then, in principle, contract and form a little galaxy (a “tidal dwarf”). However you wouldn’t expect that galaxy to be as big as this object (it’s almost the size of the Milky Way), and you’d also expect to see some other remnants around from the merger event. So we don’t really know!”

However, precisely because it is so unique and unusual, it might help astronomers solve some of the fundamental questions around the mysterious dark matter. It’s paradoxical, but the galaxy lacking dark matter could teach us a lot about dark matter itself.

Journal Reference: Pieter van Dokkum et al. A galaxy lacking dark matter. DOI 10.1038/nature25676

Breakthrough in the search for dark matter from the first ever stars

Using radio antennas no bigger than a hotel fridge, a small team of astronomers managed to glimpse into the dawn of time, and they published their findings just yesterday. But if that wasn’t dramatic enough, a new paper today reports that the same results are a paradigm shift in an even more obscure area — the readings are our first direct evidence of the existence of dark matter and yield important clues on its nature.

Scientists may have caught a glimpse of the earliest stars in the universe.

[Editor’s note] We’ve covered the first part of the findings yesterday, and you can read it in-depth here. But, if you happen to be suspicious of links or you like Andrei’s skill with a keyboard, here’s the summed-up version:

Why yesterday was a good day for science

Although it happened billions of years ago, researchers have been able to infer quite a lot about the Big Bang and the following eons. Scientists theorize that right after the big event, everything was dark, and it took a few hundred million years for the first stars to form out of the primordial soup of matter. So far, astronomers haven’t been able to pick up any signal from these stars, as our telescopes just weren’t sensitive enough. Now, using the Experiment to Detect the Global Epoch of Reionization Signature (EDGES), an array of three telescopes from remote Australia, researchers have captured the first glimpses of these ancient objects.

The oldest galaxy we’ve observed emerged around 400 million years after the Big Bang. This signal is the first thing anyone has spotted in the interval between that galaxy was formed and the so-called cosmic microwave background, 380,000 years after the birth of the Universe.

“This is really the only possible probe that we have of the time before the stars,” says Bowman, who is an experimental astrophysicist at Arizona State University in Tempe.

The small antennas in the Australian outback. Credits: CSIRO.

Before the first stars formed, the atoms’ internal states were in microwave equilibrium — they absorbed just as much radiation as they gave out. As the first stars formed, they produced light which disrupted this equilibrium, enabling the atoms to absorb more than they gave out. This is what astronomers have identified yesterday. It gives a unique insight into those early days, showing that, for instance, the initial hydrogen was much colder than originally thought (since the absorption signal was twice stronger than expected, and this correlated with temperature).

Why yesterday made for a great day for science… today!

This also shines new light on the so-called dark matter, a mysterious and invisible form of matter spread through the cosmos.

The early stages of the Universe. Credits: N.R.Fuller/National Science Foundation.

The signal Prof. Bowman’s team picked up was a radio signal at a frequency of 78 megahertz. The width of this signal’s profile was by-and-large consistent with what they expected to find, but it also had a larger amplitude that they expected — which corresponds to a deeper absorption of the signal in space. They concluded that this means the primordial gasses in the early universe were colder than we’ve estimated, reported on the finding, and presumably thought that was the end of it.

However, that one tiny detail could provide us with the first direct proof of the existence of dark matter, and the first actual clues about its nature. It’s the first direct piece of data we have on dark matter since we’ve first started thinking about it, over one century ago. In other words, that tiny detail yielded a breakthrough in the field.

“I realized that this surprising signal indicates the presence of two actors: the first stars, and dark matter,” says Prof. Barkana, Head of the Department of Astrophysics at the Tel Aviv University, who published the paper detailing the link between this signal and dark matter.

“The first stars in the universe turned on the radio signal, while the dark matter collided with the ordinary matter and cooled it down. Extra-cold material naturally explains the strong radio signal.”

Basically, all we know of dark matter is that it exists… and that we can’t see it. We know its there because we can measure its gravitational effect, but that’s about it. That’s why, in Prof. Barkana’s words, dark matter “remains one of the greatest mysteries in physics.”

“To solve it, we must travel back in time,” he says. “Astronomers can see back in time, since it takes light time to reach us. We see the sun as it was eight minutes ago, while the immensely distant first stars in the universe appear to us on earth as they were billions of years in the past.”

Based on observed gravitational effect, physicists expected dark matter particles to be very heavy, but Prof. Barkana’s results suggest that they must be less than five times as massive as a hydrogen atom. The finding has the potential “to reorient the search for dark matter,” says Barkana.

But this isn’t the only plausible explanation, and we’re still waiting for the dust to settle before any definitive conclusions can be drawn. First, as always, is sheer instrument error. A confirmation would be highly useful, given how fine the measurements the EDGES device was performing. Even the tiniest error in calibration or measurement could distort the signal, and although the researchers are confident they’ve done their best to ensure that no error slipped in, they’d also welcome any confirmation.

“We’re eager for others to confirm the result,” Bowman added.

One definitive piece of evidence in favor of Barkana’s theory could be picked up with a large array of radio antennas. He says that, according to his model, the dark matter should have produced a very specific pattern of radio waves.  Luckily for us, one such array, the SKA, the largest telescope in the world, is already under construction — if it picks up on the signal, the SKA “would confirm that the first stars indeed revealed dark matter,” concludes Prof. Barkana.

The paper, “Possible interaction between baryons and dark-matter particles revealed by the first stars” has been published today in the journal Nature.

Bowman’s paper, “An absorption profile centred at 78 megahertz in the sky-averaged spectrum” has been published in the journal Nature.

 

The galaxy Centaurus A, seen here centered. Credit: Christian Wolf & SkyMapper Team/Australian National University.

Dwarf satellite galaxies are challenging the standard cosmological model

Astronomers are puzzled by a handful of dwarf galaxies that revolve around a larger elliptical galaxy called Centaurus A in a peculiar fashion.

The galaxy Centaurus A, seen here centered. Credit: Christian Wolf & SkyMapper Team/Australian National University.

The galaxy Centaurus A, seen here centered. Credit: Christian Wolf & SkyMapper Team/Australian National University.

The galaxies’ unusual behavior doesn’t ‘fit’ within any framework described by the standard cosmological model, also known as the Lambda Cold Dark Matter cosmological model of the Universe or simply as the Lambda CDM (λCDM).

This model is our best interpretation so far of the origin, evolution, and behavior of the known universe around us, from the Big Bang to present day. The motion of Centaurus A’s galactic satellites might leave scientists scrambling for a new model that fits with the observations.

Challenging the established physics

Less massive objects are always attracted by more massive ones — such is the nature of the universe, as spurred by the force of gravity. The moon gravitates around Earth, which revolves around the sun, which in turn revolves around the Milky Way’s center of mass, corresponding to a supermassive black hole. Also revolving around the Milky Way are other, smaller galaxies called satellite galaxies. Scientists have always found it odd that our galaxy, the spiral-armed Milky Way, has several satellites that orbit in a flat plane, just like planets behave in a solar system, rather than exhibiting a random, spherical distribution as the λCDM predicts. The same has been observed in the nearby Andromeda galaxy whose satellites are also arrayed in a flat plane.

Previously, scientists have always shrugged off these surprising patterns as statistical anomalies. But the latest detailed observations of Centaurus A and its satellites add another exception to the rule. According to an international team of researchers, 14 out of the 16 satellite galaxies orbit their larger host galaxy together in the same plane. With so much evidence piling up, it’s hard to ignore the observation and discard it as a mere glitch in the matrix.

There are some ideas that might explain what the scientists are seeing. Just like the moon’s gravity leads to tides here on Earth, so can the gravity of a larger galaxy rip out stars and gas from another galaxy. Due to this interaction, it may be possible that some dwarf galaxies orbit the larger ones in a flat planet and along the same direction.

It’s not at all clear at this point, however, how stable tidal dwarf galaxies are. Without this information, it’s difficult to come to a reasonable interpretation, especially considering that the λCDM hinges on the assumption that dwarf galaxies are the building blocks of the known universe. These were the very first galaxies ever, which then merged to form larger ones, such as the Milky Way.

Another hypothesis is that, as the λCDM model implies, dark matter filaments that shape the arrangement of galaxies can be as long as 10 to 20 times the distance from Earth to Centaurus A. That’s mind-boggling scale of dark matter distribution might be what’s causing this planar structure like the one scientists are observing now.

According to model simulations with dark matter, however, only half a percent of satellite systems in the local universe at most should behave this way. But what astronomers are seeing can’t be any coincidence.

“Coherent movement seems to be a universal phenomenon that demands new explanations,” says Oliver Müller, an astronomer at the University of Basel’s Department of Physics and co-author of the new study published in Science.

While the new data is contradicting the λCDM, that doesn’t mean that the model is done for. So much about everything else scientists are tracking in the universe works within the boundary of the standard cosmological model that it would be quite foolish to discard it at the first bumps in the road. It will take far more contradictory evidence before scientists start looking for an alternative. The upcoming James Webb Space Telescope will help astronomers study more galaxies and their satellites, data that will help scientists draw better conclusions.

“At worst, we improve our understanding of galaxy formation; at best, we are led to a deeper understanding of the laws of physics,”  said astrophysicist Mike Boylan-Kolchin of the University of Texas, who commented on the study for Ars Technica. “The distribution of satellites around nearby galaxies does not yet rise to the level of a crisis driving us to a new understanding, but the results of Müller et al. raise the stakes.”