Tag Archives: early universe

Astronomers have discovered two pairs of quasars in the distant Universe, about 10 billion light-years from Earth. In each pair, the two quasars are separated by only about 10,000 light-years, making them closer together than any other double quasars found so far away. The proximity of the quasars in each pair suggests that they are located within two merging galaxies. Quasars are the intensely bright cores of distant galaxies, powered by the feeding frenzies of supermassive black holes. One of the distant double quasars is depicted in this illustration. International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva

Double trouble! Astronomers discover distant quasar pairs

Astronomers have observed two pairs of quasars in the distant Universe, closer together than any previously observed examples of similar pairings. The team followed the discovery–made with the Hubble Space Telescope and Gaia spacecraft–with spectroscopic observations made by the Gemini North Telescope.

The discovery is significant as it points towards the possible existence of supermassive black hole (SMBH) pairs. As the quasar pairs exist in merging galaxies, the finding also grants researchers an insight into how such events could have proceeded in the early Universe.

Astronomers have discovered two pairs of quasars in the distant Universe, about 10 billion light-years from Earth. In each pair, the two quasars are separated by only about 10,000 light-years, making them closer together than any other double quasars found so far away. The proximity of the quasars in each pair suggests that they are located within two merging galaxies. Quasars are the intensely bright cores of distant galaxies, powered by the feeding frenzies of supermassive black holes. One of the distant double quasars is depicted in this illustration. Labels point out the location of the quasars, the accretion disks (rings of material feeding each black hole), and the quasar host galaxies, which are in the process of merging.

It is the relatively close proximity between the quasars in the two pairings of just 10-thousand light-years that suggests to the astronomers that they belong to merging galaxies.

“We estimate that in the distant Universe, for every one thousand quasars, there is one double quasar,” says Yue Shen, an astronomer at the University of Illinois. “So finding these double quasars is like finding a needle in a haystack.”

Shen is the lead author of a paper published in the latest edition of the journal Nature Astronomy.

Quasars sit at the centre of galaxies in an area known as the active galactic nuclei (AGN) blasting out powerful jets of radiation. They are powered by SMBHs devouring material like gas and dust that surrounds them.

Quasars are so powerful that they profoundly affect the evolution of galaxies around them. This means that studying them is also a great way of learning how galaxies come together.

These particular quasars are 10-billion light-years from Earth meaning they existed just four billion years after the Big Bang. Double quasars are, in of themselves, rare, especially at such great distances. But, what makes these pairs particularly interesting is the fact they point to even rarer, hitherto undiscovered, SMBH binaries.

These two Hubble Space Telescope images reveal two pairs of quasars that existed 10 billion years ago and reside at the hearts of merging galaxies. (NASA/ STScI)

“This truly is the first sample of dual quasars at the peak epoch of galaxy formation that we can use to probe ideas about how supermassive black holes come together to eventually form a binary,” says Nadia Zakamska, Johns Hopkins University, part of the team that made the discovery.

Supermassive Implications

The team’s discovery will excite scientists currently involved in the search for SMBH binaries. Current theories suggest that as monstrous as they are these black holes, which are believed to lurk at the centre of most galaxies, do not always exist in isolation.

Alessandra De Rosa is a research astrophysicist at the National Institute of Astrophysics, Italy, and the author of a recent review paper which summarizes what we know thus far about SMBH pairs.

The animation shows the evolution of the merging between two galaxies with mass ratio of 0.25 (Galaxy mass 1 = 4 * Galaxy mass 2). Different phases can be identified, from the gravitational approach to the final coalescence of the galaxies and black holes contained in them. (Capelo, et al, 2015)

“Searching for high z dual Active Galactic Nuclei at such small separations is a fundamental piece of information to understand how SMBHs could form and grow and to probe what we know about galaxy formation and evolution,” DeRosa, who was not involved in the team’s study, tells ZME Science. “Moreover, these systems are the most direct precursors of binary SMBHs which are amongst the loudest emitters of gravitational waves in the low-frequency ranges.”

DeRosa continues by explaining that the search for these objects at such great distances is extremely challenging due to instrument limitations that prevent them from being individually distinguished.

Until now it has been believed that these pairings would find the black holes in such close proximity that they could only be distinguished by the gravitational waves launched by their eventual merger.

This new research could offer another way to at least study how such SMBH pairings come together and form binaries.

Tracking Down Quasar Pairs

As DeRosa points out, tracking down these quasar pairs at a distance of around 10-billion years was no easy task. In order to do this, the astronomers employed a novel new method that unites data from several space-based and ground-based telescopes.

It takes an extremely powerful telescope to view objects at such distances limiting the team’s choice to the Gemini North telescope in Hawai’i, and the Hubble Space Telescope. Because observing time on these telescopes is extremely limited, sweeping the entire sky for quasar pairs was out of the question.

This artist’s conception shows the brilliant light of two quasars residing in the cores of two galaxies that are in the chaotic process of merging. The gravitational tug-of-war between the two galaxies stretches them, forming long tidal tails and igniting a firestorm of star birth. (NASA/ STScI)

To work around this, the team selected 15 quasars from the 3D map created from data collected by the Sloan Digital Sky Survey (SDSS). Observations from the Gaia spacecraft were then used to narrow these 15 quasars to candidates that could actually be pairs.

The last step of the process was using Hubble to get a better look at these suspects. In this way, the team was able to confirm that two of the objects they selected were indeed quasar pairs.

Further investigation with Gemini North and its  Gemini Multi-Object Spectrograph (GMOS) instrument allowed the astronomers to resolve the quasars’ individual spectra. Locked within this light signature is information regarding the distance from Earth and the quasars’ compositions.

“The Gemini observations were critically important to our success because they provided spatially resolved spectra to yield redshifts and spectroscopic confirmations simultaneously for both quasars in a double,” says Yu-Ching Chen, part of the team and a graduate student at the University of Illinois. “This method unambiguously rejected interlopers due to chance superpositions such as from unassociated star-quasar systems.”

The Next Steps for Studying Quasar Pairs

Whilst the team is extremely confident that they have discovered quasar pairs in merging galaxies, there does remain the slight chance that they have actually captured a double image of a single quasar.

This kind of doppelganger illusion can be caused by strong gravitational lensing, the bending of light from a distant source when an object of great mass passes between it and our line of sight.

In extreme cases, this lensing can cause objects to appear at multiple points in the sky due to light being forced to take different paths across the Universe. Striking examples are so-called Einstein crosses and rings when single light sources appear at numerous points in a geometrical pattern.

An Einstein ring is an extreme example of gravitational lensing. The team are confident that this is not the source of their dual quasar discovery (ESA/Hubble & NASA)

The researchers believe that this can be discounted in the case of their research as the light from the distant quasars did not pass an intersecting foreground galaxy.

The next step for the researchers is the research for more quasar pairs, hopefully leading to the development of a census of such duos in the early universe.

“This proof of concept really demonstrates that our targeted search for dual quasars is very efficient,” Hsiang-Chih Hwang, the principal investigator of the Hubble observations and a graduate at John Hopkins University, concludes. “It opens a new direction where we can accumulate a lot more interesting systems to follow up, which astronomers weren’t able to do with previous techniques or datasets.”

Baby universes branching off of our universe shortly after the Big Bang appear to us as black holes. (Kavli IPMU)

Primordial black holes could hide a multiverse of possibilities

Before the stars and galaxies even began to form in the early Universe, some researchers believe that the cosmos could have been occupied by a multitude of tiny primordial black holes. These purely hypothetical black holes would have formed in a radically different way than larger and more familiar black holes which physicists, cosmologists, and astronomers have confirmed to exist. 

Whereas larger black holes form as a result of the death of massive stars, primordial black holes would have been born immediately after the ‘Big Bang’ when areas of high density underwent gravitational collapse. Despite having a long history in theoretical physics, primordial black holes had moved out of favour, that is until recently.

Baby universes branching off of our universe shortly after the Big Bang appear to us as black holes. (Kavli IPMU)
Baby universes branching off of our universe shortly after the Big Bang appear to us as black holes. (Kavli IPMU)

Now researchers from the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) — including Kavli IPMU members Alexander Kusenko, Misao Sasaki, Sunao Sugiyama, Masahiro Takada and Volodymyr Takhistov —  are studying the possibility of such objects existing both in the early Universe and in our current epoch.

The team believes the discovery of primordial black holes could point to a potential multiverse, with other ‘baby universes’ born alongside our own. Meaning that behind the event horizon — the point at which not even light can escape — of these primordial black holes could lurk an entire universe, hidden from view.

The scientists’ findings are documented in a paper published in the journal Physical Review Letters.

Beyond the discovery of these early black holes themselves, such an investigation could answerquestions surrounding many lingering and mysterious aspects of physics. 

Primordial Black holes and Lingering Mysteries

The team believes that the existence of primordial black holes could account for a small amount of the gravitational waves detected at the LIGO/VIRGO interferometer. Until recently, this had been ruled out as primordial black holes existing binary pairs should result in more gravitational-wave signals than we currently detect. 

Recent research has begun to illustrate how primordial black holes could exist and still produce gravitational wave signals that conform to the number detected at LIGO. 

Such objects could even explain how some heavy elements are synthesised. Should primordial black holes exist, they could either collide with neutron stars — obliterating them — or infest the centres of such stellar remnants and ‘eat them’ from the inside out. Either of these processes would lead to the release of neutron-rich material would be released. 

the team searched the Andromeda galaxy with the HSC for clues indicating the prescence of primordial black holes (Kavli IPMU/HSC Collaboration)

The synthesis of heavy elements has puzzled astrophysicists for some time, as the processes behind it rely on the presence of large numbers of neutrons, meaning primordial black holes could play a key role in providing such neutron-rich conditions. 

Perhaps more exciting than this even; the team’s research could reveal if primordial black holes comprise the majority of dark matter — the mysterious substance which makes up between 80–90% of the Universe’s total matter content.

The idea that primordial black holes could account for dark matter — or at least some of it — isn’t a new idea. But, like the discussion of these objects themselves, theories connecting them to dark matter have also fallen out of favour over recent years. 

In order to discover primordial black holes, the Kalvi team used the Hyper Suprime-Cam (HSC) of the 8.2m Subaru Telescope, a gigantic digital camera at the summit of Mount Mauna Kea, Hawaii to study the early Universe for clues.

 Searching the Early Universe for Primordial Black Holes

Because the early Universe was so dense, it would take only a small density fluctuation of around 50% to create a black hole. This means, that whilst the gravitational perturbations that created galaxies were much smaller than this, there are a variety of events in the early cosmos that could have triggered the start of such a genesis event.

One such process would be the creation of a small ‘daughter universe’ branching off from our own universe during its initial period of rapid inflation. Should this baby universe collapse a vast amount of energy would be released within its small volume, thus giving rise to a tiny black hole. 

This idea of branching Universes gets even stranger, however, should one of these baby-universes reach and exceed some critical size. General relativity suggests that if this was to happen the universe in question would exist in a state that appears different from the inside than it does from the outside. 

Hyper Suprime-Cam (HSC) is a gigantic digital camera on the Subaru Telescope ideal fr spotting primordial black holes (HSC project / NAOJ)

An observer from with the baby universe would see it as an expanding universe, whilst an observer outside the event horizon would see the baby universe as a black hole. This means that in both cases, the event horizon of the primordial black hole hides its internal structure — and an entire universe. 

The team’s paper points to a scenario in which primordial black holes are created by this nucleation of what they term ‘false vacuum bubbles.’ 

The fact that primordial black holes have thus far escaped detection indicates it is going to take an extremely powerful instrument to see the Universe in such a way that these multiverse camouflaging objects can be spotted.

Fortunately the HSC fits the bill.

The Hyper Suprime-Cam sees the Big Picture

As the paper’s authors describe, thanks to its unique capability to picture the entire Andromeda galaxy every few minutes, the HSC could be the ideal instrument to capture primordial black holes. This imaging can be achieved with the aid of gravitational lensing, the curvature of light by an object of great mass.

The team used gravitational lensing, the curvature of light by objects with tremendous mass, to help identify primordial black holes. (Kavli IPMU/HSC Collaboration)
The team used gravitational lensing, the curvature of light by objects with tremendous mass, to help identify primordial black holes. (Kavli IPMU/HSC Collaboration)

As a primordial black hole passes the line of sight to a bright object such as a star, the curvature it causes in spacetime results in a momentary brightening of the object or an apparent shift in position. 

The greater the mass, the more extreme the curvature and thus the stronger the effect meaning that the astronomers can measure the mass of the lensing object. This effect only lasts an extremely brief time, however.

Because the HSC can see the entire galaxy, it can simultaneously observe up to one hundred million stars — giving astronomers a good chance of catching a transiting primordial black hole. 

The team have already identified a prime candidate for a ‘multiverse’ hiding primordial black hole in the first run of HSC observations. The object had a mass around that of the Moon and has inspired the team to conduct further observations, thus widening their search and possibly finding a solution to some of physics’ most pressing mysteries. 

Original Research

Kusenko. A., Sasaki. M., Sugiyama. S., et al, [2021], ‘Exploring Primordial Black Holes from the Multiverse with Optical Telescopes,’ Physical Review Letters, [https://doi.org/10.1103/PhysRevLett.125.181304]

With the help of ESO’s Very Large Telescope (VLT), astronomers have found six galaxies lying around a supermassive black hole, the first time such a close grouping has been seen within the first billion years of the Universe. This artist’s impression shows the central black hole and the galaxies trapped in its gas web. The black hole, which together with the disc around it is known as quasar SDSS J103027.09+052455.0, shines brightly as it engulfs matter around it. (ESO/L. Calçada)

‘Cosmic Web’ of a Supermassive Black Hole Ensnares Six Galaxies

Astronomers have discovered a tremendous cosmic web in the early Universe. Trapped within its threads are six galaxies feeding gas to a central supermassive black hole. 

Astronomers have made a startling discovery in the early Universe: six galaxies suspended in the cosmic web of a supermassive black hole. The finding represents the first time such a grouping has been found when the Universe was young —  just under a billion years after the ‘Big Bang.’

The cosmic web with its suspended galaxies seems to conform to the theory that supermassive black holes grew to monstrous sizes thanks to the fact that they sat at the centre of web-like structures with gas and dust to feed them. 

“The title of our article  —  ‘Web of the Giant’ — may suggest the idea of the supermassive black hole as a giant black spider at the centre of the web, with that web providing both the trap and the path to carry the material that feeds the giant at the centre,” Marco Mignoli, an astronomer at the National Institute for Astrophysics (INAF) in Bologna, Italy, tells ZME Science. “The importance of our work is that we are the first group to discover the galaxies that inhabit the web.”

With the help of ESO’s Very Large Telescope (VLT), astronomers have found six galaxies lying around a supermassive black hole, the first time such a close grouping has been seen within the first billion years of the Universe. This artist’s impression shows the central black hole and the galaxies trapped in its cosmic web. The black hole, which together with the disc around it is known as quasar SDSS J103027.09+052455.0, shines brightly as it engulfs matter around it. (ESO/L. Calçada)

The new observation of these six faint galaxies trapped in a web of filament ‘threads’ comprised of hot gas, stars, and galaxies surrounding a supermassive black hole, was made with the aid of the ESO’s Very Large Telescope (VLT) and is described in a paper published in the journal Astronomy and Astrophysics.

As is only fitting for a supermassive black hole ‘spider’, the web in which it sits is of tremendous size —  300 times that of the Milky Way. “From this filamentous structure, the giant black hole is probably accumulating material that has allowed it to grow extremely fast, reaching one billion solar masses in less than a billion years,” Mignoli, author of the paper, adds. “The galaxies stand and grow where the filaments cross, and streams of gas —  available to fuel both the galaxies and the central supermassive black hole —  can flow along the filaments.”

Supermassive Black Hole Feeding in the Early Universe

The light from this cosmic web has traveled to us from a time when the Universe was just 0.9 billion years old. This represents not just a time at which the first generation of black holes have formed from collapsing stars, but also the point where the faster-growing of these black holes have grown to truly monstrous sizes.

https://youtu.be/BHRYrINUigE

The question of how supermassive black holes managed to grow so rapidly has puzzled scientists for decades, with researchers unable to detect exactly how these black holes could obtain so much ‘black hole fuel’ so quickly. The findings seem to provide an answer, suggesting that the cosmic web and the galaxies within it contain enough gas to quickly grow the central black hole into a supermassive giant. 

“[The study] provides confirmation of several theories, that these primordial supermassive black holes are found at the center of immense filamentous structures composed by hot gas and by galaxies that are actively forming stars,” Mignoli says. “Such structures — ‘cosmic webs’ —  can provide the necessary material for the central black hole to grow extremely fast.”

Whilst this isn’t the first time astronomers have spotted a ‘cosmic web’, it is the first time its been occupied by a supermassive black hole ‘spider’ at its heart. 

 “Similar, early large scale structures have already been found, but none with a supermassive black hole at their centre,” Roberto Gilli, an astronomer at INAF in Bologna and co-author of the study, tells ZME Science. “Our work has placed an important piece in the largely incomplete puzzle that is the formation and growth of such extreme, yet relatively abundant objects so quickly after the Big Bang.”

What the researchers can’t be so sure of is how these black holes initially formed, the process by which they are ‘fed’, or how the cosmic web itself developed. “We have no observational evidence of from which seeds these giant black holes are grown,” Mignoli explains. “The structures are too far away, the gas flows too faint to be detected. And also from a theoretical point of view, there are problems that are too difficult to solve.”

One possibility is that cosmic webs such as that discovered by the team formed as a result of the gravitational influence of dark matter haloes. These bunches of mysterious substance — which makes up 90% of the matter in the known Universe — could have drawn together tremendous amounts of gas in the early Universe. From there, the gas and dark matter may have formed the matrix of a cosmic web. 

Mignoli explains that one of the most intriguing lingering questions is what process allows material to be transported from an intergalactic scale to the size of a black hole’s accretion disc — in the order of parsecs. 

Gilli offers some suggestions regarding this feeding process, albeit ones that are currently unsupported by observations: “According to theory, dense environments are a necessary but not sufficient condition,” Gilli explains. “[The feeding mechanism] could be related to gas availability in these dense regions: large reservoirs mean that there is enough gas to fuel the BH and grow fast. Some theories propose that direct gas streams through the web can fall directly into the black holes and grow them.”

Gilli also adds that another way by which supermassive black holes could gather tremendous mass is via galactic mergers. And, the researcher adds, the cosmic web could play a role in this process too. “Another way this web can aid black hole growth is through galaxy mergers: within these dense, filamentary environments, mergers of gas-rich galaxies are more frequent, and mergers normally destabilize gas within galaxies and allow it to fall within the black holes at their centres.”

Spider Hunting: Searching the Universe for more ‘Occupied’ Cosmic Webs

The galaxies observed by the team are some of the faintest ever studied by astronomers, and required employing the tremendous power of the VLT — located at the ESO’s Paranal Observatory in the Atacama Desert, Chile — for several hours. Thus, with the aid of the VLT’s MUSE and FORS2 instruments, the team was able to confirm the six galaxies were linked to a central supermassive black hole.

“Early supermassive black holes are among the most challenging systems in extragalactic astrophysics,” Gilli explains. “We designed this experiment more than 8 years ago in the hope of confirming theory expectations. Observations of such systems are painful and only by cumulating several years of effort we could finally confirm the existence of such a structure.”#

This image shows the sky around SDSS J103027.09+052455.0, a quasar powered by a supermassive black hole surrounded by at least six galaxies. This picture was created from images in the Digitized Sky Survey 2. (ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin)

The aim now is to find more examples of such structures, which Gilli believes should be fairly common in the early Universe. Perhaps then we can start to answer the questions that surround the formation and evolution of such events. 

“We’d like to confirm more structure like this and also to discover populations of SMBHs in the early Universe that should exist but are still missing from our census,” Gilli says. “There are billion-solar-mass black holes at galaxies’ centres and we still do not know where they come from. And there is even more mystery surrounding such systems in the early Universe.”

Mignoli. M., Gilli. R., Decarli. R., et al, [2020], ‘Web of the giant: Spectroscopic confirmation of a large-scale structure around the z=6.31 quasar SDSS J1030+0524,’ Astronomy and Astrophysics. 

Recent discoveries have challenged ideas about how galaxies form, including how early in the Universe's history they developed.

What’s My Age Again? New Discoveries May Spark a Rethink of Galaxy Formation

Many mysteries surround conditions in the early Universe, chief amongst these is the question of how and when galaxies began to form. At some point in the Universe’s history, gravitational instability brought together increasingly larger clumps of matter, beginning with atoms, dust, and gas, then stars and planets, clusters and then massive galaxies.

Whilst early protogalaxies may have formed as early as a few hundred million years after the Big Bang, the first well-formed galaxies with features such as spiral arms, rings and bars are thought to have only formed around 6 billion years into the Universe’s 13.8 billion year lifetime. 

Astronomy has, in general, confirmed this. With closer and thus later galaxies displaying characteristics such as rings, bars and spiral arms, like our own home, the Milky Way. Features lacking in more distant, earlier galaxies. 

New discoveries, however, are challenging this accepted view, with three recent pieces of research, in particular, suggesting that well-ordered and massive galaxies existed much earlier in the Universe than previously believed. This either means that the formation of galaxies began much earlier than expected or progressed much faster than many models suggest.

As a consequence scientists may have to refine models of galaxy formation to account for much earlier or much more rapid evolution.

A European team of astronomers have found no evidence of the first generation of stars, known as Population III stars when the Universe was less than one billion years old, one of three lines of evidence that suggests galaxies may have begun to form earlier in the Universe's history than current models imply. (ESA/Hubble, M. Kornmesser)
A European team of astronomers have found no evidence of the first generation of stars, known as Population III stars when the Universe was less than one billion years old, one of three lines of evidence that suggests galaxies may have begun to form earlier in the Universe’s history than current models imply. (ESA/Hubble, M. Kornmesser)

The key to solving the mystery of how soon after the Big Bang galaxies with definitive shapes and features such as thin discs and spiral arms formed begins with examining theories that describe this formation. One family of theories which implies these processes occur over a prolonged period of time, and another, that suggests formation can proceed much more quickly.

Bottom’s Up! Did Formation Start Earlier or Proceed Quicker?

The simplest model of galaxy formation suggests that at a time when the Universe was mostly hydrogen and helium, such structures emerged from dense clouds of gas that collapsed under their own gravity. This so-called ‘monolithic model’ was the first suggested formation process for galaxies and the stars that comprise them and is referred to as a ‘bottom-up’ or hierarchical formation model.

There are also ‘top-down’ formation models that suggest galaxies may have emerged from larger conglomerates of matter that collapsed in a similar fashion but then went on to break apart, but these currently aren’t favoured by most cosmologists. 

Researchers use advanced simulations to create merger trees such as the two examples above. These diagrams demonstrate how mergers can enable galaxies to grow to massive size in a relatively short space of time. Left: ESA/NASA Right: M.Merrifield/ University of Nottingham

Under the influence of gravity, gas and dust collapse into stars which are drawn together as clusters, then superclusters, and finally galaxies. The question is, how do galaxies grow and develop their characteristics? 

One idea suggests that the seed of a galaxy continues to accumulate gas and dust, slowly growing to massive size. When it reaches gigantic proportions, this galaxy is able to gobble up clusters of stars and even smaller galaxies. This process should be fairly slow, however, glacially so at first, in fact, accelerating once smaller galaxies begin to be absorbed. 

If this is the predominant formation mechanism for galaxies, then what we shouldn’t see in the early universe, before about 6 billion years after the Big Bang, are disc-like massive galaxies or spiral armed galaxies like the Milky Way. Further out in space and thus further back in time, irregulars galaxies and amorphous blobs should be favoured heavily. Unless that is, galactic formation got a serious head-start.

But, there is another theory of galactic evolution. What if galaxy growth progresses predominantly through merger processes?

Rather than a galaxy waiting until it grows massive in size to start accumulating its smaller counterparts, mergers between similar-sized galaxies could be the driving factor in creating larger galaxies. This would mean that the process of galaxy formation could proceed much more quickly than previously believed.

In either case, what we should see is massive galaxies well-formed with characteristics like disks, bars, and spiral arms way further out into space, and thus further back in time. 

It just so happens that is exactly what astronomers are starting to find. 

Should’ve Put a Ring on it!

One such line of evidence for a more rapid form of galactic formation or a much earlier start, comes in the distinctive doughnut-like shape of a collisional ring galaxy discovered 11 billion-light-years away. This means this “cosmic ring of fire” — similar in mass to the Milky Way and notable for the massive ‘hole’ in its centre which is three million times the distance between the Earth and the Sun — existed when the Universe was just 2.7 billion years old. Far earlier than predicted. 

An artist’s impression of the ring galaxy R5519 (James Josephides, Swinburne Astronomy Productions)

Dr Tiantian Yuan, of Australia’s ARC Centre of Excellence for All-Sky Astrophysics in 3 Dimensions (ASTRO 3D) was part of a group that successfully gave the ring galaxy — designated R5519 — an age. 

“It is very a curious object, one that we have never seen before, definitely not in the early Universe,” explains Yuan, a specialist in studying galactic features like spiral arms. “R5519 looks like a corona galaxy, but it isn’t.”

So, even if R5519 is striking, how does this imply that models of galaxy evolution could be inaccurate? The answer lies in how collisional ring galaxies such as this are created. 

Yuan explains that the ‘hole’ at the centre of R5519 was created when a thin disk-like galaxy was ‘shot’ by another galaxy hitting head-on, just like a bullet hitting a thin paper target at a shooting range. 

“When a galaxy hits the target galaxy — a thin stellar disk — like a bullet, head-on, it causes a pulse in the disk of the victim galaxy,” Yuan says. “The pulse then induces a radially propagating density waves through the target galaxy that form the ring.”

1. A thin stellar disk as a target or ‘victim’ galaxy. Another galaxy approaches on a head-on trajectory like a bullet. 2&3. Collision through the centre of the thin target galaxy. 4. The ‘bullet galaxy’ moves on as a perturbation spreads through the target galaxy. 4. The perturbation creates a ring-like structure. ( James Josephides, Swinburne Astronomy Productions/Robert Lea)
1. A thin stellar disk as a target or ‘victim’ galaxy. Another galaxy approaches on a head-on trajectory like a bullet. 2&3. Collision through the centre of the thin target galaxy. 4. The ‘bullet galaxy’ moves on as a perturbation spreads through the target galaxy. 4. The perturbation creates a ring-like structure. ( James Josephides, Swinburne Astronomy Productions/Robert Lea)

Yuan explains that at one time astronomers had expected to find more collisional ring galaxies in the young universe, simply because there were more galactic collisions progressing at that time. “We find that is not the case,” she continues. “The young universe might have more collisions and bullets, but it lacks thin stellar disks to act as targets… or so we thought.”

Here’s where the problem lies, thin stellar disks that serve as targets in this cosmic firing range aren’t supposed to exist so early in the Universe’s history according to currently favoured cosmological models.

“Our discovery implies that thin stellar disks similar to our Milky Way’s are already developed for some galaxies at a quarter of the age of the universe.”

This is a composite image of the ring galaxy R5519 compiled from single-colour images taken by the Hubble Space Telescope. (Tiantian Yuan/Hubble Space Telescope)

Yuan and her team’s findings show galactic structures like thin disks and rings could form 3 billion years after the Big Bang. The researcher points to another piece of research that supports the idea of structured galaxies in the early Universe.

“The first step in disk formation is to form a disk at all — an object that is dominated by rotation,” Yuan says. “This is why the recent discovery of the ‘Wolfe disk’ is truly amazing — it pushes the earliest formation time of a large gas disk to much earlier than we previously thought.”

Who’s Afraid of the Big Bad Wolfe? 

The discovery Dr Tiantian Yuan refers to is the identification of a massive rotating disk galaxy when the Universe was just 1.5 billion years old. The galaxy — officially named DLA0817g — is nicknamed the ‘Wolfe Disk’ in tribute to the late astronomer Arthur M. Wolfe, who first speculated about such objects in the 1990s.

ALMA radio image of the Wolfe Disk, seen when the universe was only ten per cent of its current age. (ALMA (ESO/NAOJ/NRAO), M. Neeleman; NRAO/AUI/NSF, S. Dagnello)

The fact that the Wolfe Disk —which is  spinning at tremendous speeds of around 170 miles per second — exists when the Universe was just 10% of its current age, strongly implies rapid galactic growth or the early formation of massive galaxies.

“The ‘take-home’ message from the discovery of a massive, rapidly rotating disk galaxy that resembles our Milky Way but formed only 1.5 billion years after the Big Bang, is that galaxy formation can proceed rapidly enough to generate massive, gas-rich galaxies at early times,” says J. Xavier Prochaska, professor of astronomy and astrophysics at the University of California Sant Cruz, and part of a team that discovered the Wolfe Disk. 

The team behind the Wolfe Disk discovery posit the idea that its existence and the fact that it is both massive and well-formed indicate that the slow accretion of gas and dust may not be the dominant formation mechanism for galaxies. Something much more rapid could be at play. 

“Most galaxies that we find early in the universe look like train wrecks because they underwent consistent and often ‘violent’ merging,” says Marcel Neeleman of the Max Planck Institute for Astronomy in Heidelberg, Germany, who led the astronomers. “These hot mergers make it difficult to form well-ordered, cold rotating disks as we observe in our present universe.”

The Wolfe Disk as seen with ALMA (right — in red), VLA (left — in green) and the Hubble Space Telescope (both images — blue). In radio light, ALMA looked at the galaxy’s movements and mass of atomic gas and dust and the VLA measured the amount of molecular mass. In UV-light, Hubble observed massive stars. The VLA image is made in a lower spatial resolution than the ALMA image and therefore looks larger and more pixelated. (ALMA (ESO/NAOJ/NRAO), M. Neeleman; NRAO/AUI/NSF, S. Dagnello; NASA/ESA Hubble)
The Wolfe Disk as seen with ALMA (right — in red), VLA (left — in green) and the Hubble Space Telescope (both images — blue). In radio light, ALMA looked at the galaxy’s movements and mass of atomic gas and dust and the VLA measured the amount of molecular mass. In UV-light, Hubble observed massive stars. The VLA image is made in a lower spatial resolution than the ALMA image and therefore looks larger and more pixelated. (ALMA (ESO/NAOJ/NRAO), M. Neeleman; NRAO/AUI/NSF, S. Dagnello; NASA/ESA Hubble)

If the Wolfe Disk grew as the result of the accumulation of cold gas and dust, Prochaska explains that this leaves questions unanswered about its stability: “The key challenge, is to rapidly assemble such a large gas mass while maintaining a relatively quiescent, thin and rotating disk.”

Of course, sometimes it can be the absence of something that provides evidence that a theory, or family of theories is inaccurate, as the following research exemplifies.

Further away and further back in time: Some of our Stars are Missing

The Hubble Space Telescope (HST) allows astronomers to stare back in time to when the Universe was just 500 million years old, allowing researchers to finally investigate the nature of the first galaxies and could deliver more contradictions to current cosmological models just as the Wolfe Disk and R5519 have.

Results recently delivered by the HST and examined by a team of European astronomers confirm the absence of the primitive stars when the Universe was just 500 million years old. 

These early stars — named Population III stars — are thought to be composed of just hydrogen and helium, with tiny amounts of lithium and beryllium, reflecting the abundances of these elements in the young Universe.

This image from the NASA/ESA Hubble Space Telescope shows the galaxy cluster MACS J0416. This is one of six clusters that was studied by the Hubble Frontier Fields programme, which yielded the deepest images of gravitational lensing ever made. Scientists used intracluster light (visible in blue) to study the distribution of dark matter within the cluster. (NASA, ESA, and M. Montes (University of New South Wales, Sydney, Australia))

A team of astronomers led by Rachana Bhatawdekar of the European Space Agency confirmed the absence of this first generation of stars by searching the Universe as it existed between 500 million years to 1 billion years into its history. Their observations were published in a 2019 paper with further research due to publish in Monthly Notices of the Royal Astronomical Society as well as being discussed at a press conference during the 236th meeting of American Astronomical Society.

“Population III stars are extremely hot and massive and so they are much bluer in colour than normal stars,” Bhatawdekar says. “We, therefore, looked at the ultraviolet colours of our galaxies to see exactly how blue they looked.”

The team found even though the galaxies they observed were blue, they weren’t blue enough to have stars with very low metals–by which, astronomers mean any element heavier than hydrogen and helium, such as oxygen, nitrogen, carbon, iron etc…

“What this tells us is that even though we are looking at a Universe that is just 500 million years old, galaxies have already been enriched by metals of significant amount,” Bhatawdekar. “This essentially means that stars and galaxies must have formed even earlier than this very early cosmic time.”

Thus the team’s observations imply that stars had already begun to fade and die by this point in time, shedding heavier elements back into the Universe. These elements would go on to form the building blocks of later generations of stars. 

This piece of the puzzle would seem to suggest that the presence of massive galaxies is not a factor that arises as the result of rapid growth, but that the growth processes began earlier.

“We found no evidence of these first-generation Population III stars in this cosmic time interval,” explains Bhatawdekar. “These results have profound astrophysical consequences as they show that galaxies must have formed much earlier than we thought.”

Finding More Evidence of Early Galaxy Formation

For Bhatawdekar the further investigation on conditions in the early Universe will only really open up with the launch of the James Webb Space Telescope.

“Whilst we found is that there is no evidence of existence of Population III stars in this comic time but there are many low mass/faint galaxies in the early Universe,” she says. “This suggests that the first stars and first galaxies must have formed even earlier than this incredible instrument Hubble can probe.

“The James Webb Space Telescope, which is scheduled to be launched next year in 2021, will look even further back in time as far as when the Universe was just 200 million years old.”

Even before the launch of the James Webb Space Telescope, and as if to dismiss the idea that these results could be a fluke and thus not indicative of a wider shift towards earlier massive galaxies, Tiantian Yuan describes further findings yet to be published. 

“I have actually found more collisional ring galaxies in the early universe!” exclaims Yuan. “There is a cool one that is gravitationally lensed, giving us a sharper view of the ring.

“I can tell you that this new ring is 1 billion years older than R5519, and it looks a lot different from R5519 and more like rings in our nearby Universe.”

As we refine our ideas of galaxy evolution we are likely to find that when presented with two conflicting theories, the truth is that which lies somewhere in-between. Thus, as we observe the formation of galaxies currently progressing, the mergers between galaxies, and complex structures in the Universe’s history we may find that galactic evolution may progress both slowly and quickly. 

Hopefully, this mix of models will also deliver an accurate recipe for how spiral arms, rings, and bars arise from thin disks. Something currently lacking.

“What these discoveries mean is that we are entering a new era that we can ask the question of how different structures of galaxies first formed,” Yuan explains. “Galaxies do not form in one go; some parts were assembled first and others evolved later. 

“It is time for the models to evolve to the next level of precision and accuracy. Like a jigsaw puzzle, the more pieces we reveal in observations, the more challenging it is to get the theoretical models correct, and the closer we are to grasp the mastery of nature.”


Sources and further reading

Yuan. T, Elagi. A, Labbe. I, Kacprzak. G. G, et al, ‘A giant galaxy in the young Universe with a massive ring,’ Nature Astronomy, [2020].

Neeleman. M, Prochaska. J. X, Kanekar. N, Rafelski. M, [2020], ‘A cold, massive, rotating disk galaxy 1.5 billion years after the Big Bang,’ Nature, [https://www.nature.com/articles/s41586-020-2276-y]

Bhatawdekar. R, Conselice. C. J, Margalef-Bentabol. B, Duncan. K, ‘Evolution of the galaxy stellar mass functions and UV luminosity functions at z = 6−9 in the Hubble Frontier Fields,’ Monthly Notices of the Royal Astronomical Society, Volume 486, Issue 3, July 2019, Pages 3805–3830, [2019], https://doi.org/10.1093/mnras/stz866

Quark-Gluon Plasma that filled the early Universe investigated by ALICE

The secrets of the Quark-Gluon Plasma that filled the early universe are being unlocked by the ALICE collaboration at CERN with the first measurement of the flow of bottomonium particles.

Quark-Gluon Plasma that filled the early Universe investigated by ALICE (Author's Collection)

Quark-Gluon Plasma that filled the early Universe investigated by ALICE (Author’s Collection)

 

In a paper presented at the European Physical Society’s conference on high-energy physics, the ‘A Large Ion Collider Experiment’ (ALICE) collaboration has documented the first-ever measurement of the flow of a heavy meson particle — bottomonium.

The measurement of particles like bottomonium — a type of ‘upsilon’ particle — helps the researchers understand the Quark-Gluon Plasma (QGP) that filled the hot, dense early universe. 

By observing pairs of ‘heavy electrons’ — known as muons — produced by the decay of bottomonium, the team discovered bottomonium particles have small values of elliptic flow — a measure of how uniform energy and momentum is distributed across the particles when viewed from the beamline. 

This is quite unexpected as all other hadrons investigated thus far have exhibited significant elliptic flow. 

David Evans, a professor of high energy physics at the University of Birmingham, leads the UK participation in ALICE.

He says: “ Elliptical flow measurements in ALICE show that the Quark-Gluon Plasma flows like an almost perfect liquid, with the light quarks (up, down, strange, and charm) flowing with the system.”

“The fact that no significant elliptical flow is seen for the bottomonium suggests b-quarks are only produced in the initial collision of the lead ions, before the QGP is formed.”

The ALICE team’s results seem to support existing theories that bottonium and other upsilon particles split into their constituents during the early stages of their interactions with plasma.

This gives the researchers a better insight at the conditions in the early moments of the universe when it was filled with a plasma composed of free quarks and gluons. 

Evans continues: “This makes b-quarks (and particles made up of b-quarks) an ideal probe for studying the QGP as they experience the entire evolution of the system.”

Bottomonium particles — probing the Quark-Gluon Plasma at the dawn of the universe

Taking a trip through the ‘particle zoo’ to discover what these bottomonium particles actually are, helps us understand their role in the ALICE experiment. 

The six known types of quarks on the left and how they come together to form protons and neutrons on the right
The six known types of quarks on the left and how they come together to form protons and neutrons on the right

Bottonium is a heavy meson — particles which consist of a quark and its own antiparticle. In the case of bottomonium, a bottom (or beauty quark) — b quark — and its antiparticle counterpart.

These subatomic particles are extremely unstable, existing for short periods of time and only at high energies before decaying into other particles. When bottomonium decays it leaves behind a pair of ‘heavy electrons’ called muons. 

Bottomonium particles — which are formed in the LHC by the violent collision of heavy lead-lead ions — provide an excellent probe of the Quark-Gluon Plasma which filled the universe just a few millionths of a second after the big bang. 

Being produced so early in the collision event means bottomonium particles ‘experience’ the entire evolution of the plasma — from the moment it is produced to the moment it cools down and enters a state in which hadrons can form.

This extremely early stage in the universe’s evolution would have been the only time in history that quarks and gluons existed freely in plasma and not bound together in a state called ‘confinement’ in protons, neutrons and other hadrons.

These particles were only able to exist in this free state because of the incredible heat in the universe at this point. In our era, quarks and gluons are never observed as free particles.

Thus, it takes a tremendous amount of energy, to recreate these huge temperatures. At the moment, the Large Hadron Collider (LHC) is the only piece of apparatus on Earth capable of doing this, with collisions in the LHC able to generate temperatures a 100 thousand times hotter than the Sun. 

At these temperatures, protons and neutrons ‘melt’, freeing quarks and gluons from confinement, thus creating a Quark-Gluon Plasma and allowing them to form short-lived, unstable particles like bottonium. 

ALICE: Collision queen

The ALICE collaboration — consisting of over a 1000 scientists operating a 10-thousand-tonne, 16m tall detector buried 56m under the Alps — achieves this high-energy feat by slamming together beams of lead ions rather than the proton-proton collisions used in other LHC experiments. 

The decay of upsilon particles — another type of meson — into muon pairs as the result of a lead-lead collision. The red lines track the two muons the orange lines track the other particles produced (CERN)
The decay of upsilon particles — another type of meson — into muon pairs as the result of a lead-lead collision. The red lines track the two muons the orange lines track the other particles produced (CERN)

The benefit of colliding lead ions is that, as ALICE is looking to create Quark-Gluon Plasma, the more quarks available to it, the better the chance of observing something significant. 

A single proton and neutron each contain three quarks but as lead ions contain at least 56 protons and at least 204 neutrons this leaves the team with far more quarks to play with. 

ALICE then measures this plasma as it expands and cools, but it is still unable to measure the particles created directly— instead deducing the presence and properties of QGP from the signatures on pairs of muons it produced by decay. 

One of these signatures is the elliptic flow — the collective movement of the produced particles determined by several factors like particle type, mass, the angle at which the particles meet and the momentum they possess as they collide —  which is what the team measured. The flow is created by the expansion of hot plasma after the collision of the lead ions.

Upgrading ALICE: More collisions. More Quarks. More Results

Perhaps the most promising thing about ALICE’s mission to probe the early universe and its conditions is the fact that the forthcoming high-luminosity upgrade only promises to yield more data for researchers to investigate.

The ALICE Experiment is about to be revitalised (CERN)

The upgrade — which CERN hopes will be operational by 2021— aims to increase the luminosity of the LHC by a factor of 10. Luminosity, as described in reference to particle accelerators, is proportional to the number of collisions that occur. Thus increasing the luminosity also means increasing the number of collisions.

As an example of the usefulness of this upgrade, whereas the LHC produced 3 million Higgs boson particles in 2017, the High-Luminosity LHC is expected to produce 15 million per year.

In addition to the High-Luminosity upgrade — on which work began in 2018 — ALICE will also several other upgrades and improvements. As a result of these improvements, the ALICE team expect an overall gain of 100 times the current results.

Evans says: “With this huge increase in statistics and a new inner detector in ALICE, we will be able to measure particles made of b-quarks with much higher precision.”

As such, the experiment stands a very good chance of significantly improving our knowledge of the quark-gluon plasma and the conditions in the early universe, with these new bottomonium results pointing the way.

Evans concludes: “[The upgrades] allow us to probe the properties of the QGP in much more detail and hence learn more about the evolution of the early universe.”

New mathematical model analyzes early Universe

Swiss physicists have developed a new model to chart the early development of the Universe in better detail than ever before. Their code incorporates Einstein’s theory of general relativity as well as the existence of gravitational waves – which were just confirmed last week.

The Big Bang theory is the prevailing cosmological model for the universe from the earliest known periods. The model postulates that the universe expanded from a very high density and high temperature state, and it confirms and explains a series of observed phenomena – in other words, the observed data confirms the theory. But the timeline and early development universe still remains an area of hot debate, and this model could step in to answer some questions.

In the first phase, the very earliest universe was so hot, or energetic, that initially no matter particles existed or could exist perhaps only fleetingly. According to prevailing scientific theories, at this time the distinct forces we see around us today were joined in one unified force. The fact that we can even attempt to study, let alone model this early development is simply mind-blowing. The model is more accurate than all its predecessors, its creators say. It uses Einstein’s general relativity instead of Newton’s laws.

“This process is mainly governed by gravity, which is the dominant force on large scales,” the paper writes. “At present, a century after the formulation of general relativity, numerical codes for structure formation still employ Newton’s law of gravitation.”

The team from the University of Geneva analysed a cubic portion in space, consisting of 60 billion zones, each containing a particle (a portion of a galaxy). They modeled how all these particles move in relation to each other, plugging in data from Einstein’s equations, and using the UNIGE LATfield2 library.

“This conceptually clean approach is very general and can be applied to various settings where the Newtonian approximation fails or becomes inaccurate, ranging from simulations of models with dynamical dark energy or warm/hot dark matter to core collapse supernova explosions,” explains the new paper,published in the journal Nature Physics.

Their results are significant in more than one way. Directly, it puts a tangible size on the early universe, estimating the size of different early clusters. But on the other hand, this code will be made publicly available, so it could prove even more useful for people studying particular cosmological aspects – such as dark energy, which is estimated to make up 70% of the known universe. The code will also enable physicists to test the general theory of relativity on an unprecedented scale.

We’re zooming in to the birth of the Universe