The two galaxies in the upper-right part of the image seem to be interacting with each other — potentially even merging.
NGC 7764A lies some 425 million light-years from Earth, in the constellation Phoenix, first described 400 years ago, on a celestial atlas called Uranometria. Although it’s so far away, Hubble was able to snap this image using both its Advanced Camera for Surveys (installed in 2002) and Wide Field Camera 3 (the most technologically advanced visible-light camera on Hubble, installed in 2009). Both are advanced systems designed to capture images deep in space.
The two right-side galaxies appear to be dancing around each other — a dance that is also potentially affected by the bowling-ball shaped galaxy on the right side of the picture. It’s not uncommon for galaxies to interact and even collide, although this process happens very slowly, and is not technically a collision (since galaxies have more empty space than stars and planets), but rather gravitational interactions between the components that make up the two galaxies. Colliding may cause the two galaxies to merge, if they don’t have enough momentum to continue traveling after the collision. When this happens, the two galaxies eventually fall back on each other and merge into one galaxy. When galaxies just pass through each other without merging, they mostly retain their material and overall shape.
It’s not clear which of these processes is going on here, or if there’s another process altogether — although a head-on collision appears unlikely. As NASA explains, the galaxy in the lower left may also be involved, given that it is relatively close. The European Space Agency (ESA) also seems pretty stoked about the shape the two galaxies are making as they interact.
“By happy coincidence, the collective interaction between these galaxies has caused the two on the upper right to form a shape, which from our solar system’s perspective, resembles the starship known as the USS Enterprise from Star Trek,” an ESA text notes.
The space agency also points out just how clunky the naming of these galaxies is. The three galaxies are called NGC 7764A1, NGC 7764A2, and NGC 7764A3, respectively. Astronomers need these complex but specific names to make sure they know exactly what object they’re talking about and prevent any confusion.
“This rather haphazard naming makes more sense when we consider that many astronomical catalogs were compiled well over 100 years ago, long before modern technology made standardizing scientific terminology much easier,” the article adds.
“As it is, many astronomical objects have several different names, or might have names that are so similar to other objects’ names that they cause confusion.”
Black holes are the most massive objects in the universe. Their gravitational pull is so strong that nothing can escape it — not even light. But according to a new NASA study, black holes may play a more complex role in galactic ‘ecosystems’. Specifically, a black hole was found to be contributing to the formation of a new star in its vicinity, offering tantalizing clues about how massive black holes develop in the first place.
A stellar nursery
Some ten years ago, Amy Reines, then a graduate student, discovered a black hole in a galaxy about 30 million light-years away from Earth, in the southern constellation Pyxis. She knew something was off right away, but it wasn’t until recently that new Hubble observations shed light on the situation.
“At only 30 million light-years away, Henize 2-10 is close enough that Hubble was able to capture both images and spectroscopic evidence of a black hole outflow very clearly. The additional surprise was that, rather than suppressing star formation, the outflow was triggering the birth of new stars,” said Zachary Schutte, Reines’ graduate student and lead author of the new study.
The galaxy, called Henize 2-10, is a so-called “starburst” galaxy — a galaxy where stars are being formed at a much higher rate than normal, around 1,000 times faster. The galaxy is also relatively small — a so-called dwarf galaxy — and has a black hole at its center, much like the Milky Way.
Researchers were already aware of an unusual cocoon of gas in the area, but Hubble managed to also image an outflow linked to the central black hole. Although the process is not fully understood, astronomers do believe that black holes (or at least some black holes) do have an outflow despite their massive gravity. In Henize 2-10, this outflow moves at about a million miles per hour, slamming into the gas cocoon — and as it turns out, newborn stars follow the path of the outflow.
In large galaxies, the opposite happens: material falling towards the black hole forms jets of plasma that don’t allow the formation of stars. But apparently, in the less-massive Henize 2-10, the outflow has just the right characteristics to precipitate new star formation. Previously, studies mostly focused on larger galaxies, where there is more observational evidence. Dwarf galaxies are still understudied, and it’s only thanks to Hubble that researchers were able to study this.
“Hubble’s amazing resolution clearly shows a corkscrew-like pattern in the velocities of the gas, which we can fit to the model of a precessing, or wobbling, outflow from a black hole. A supernova remnant would not have that pattern, and so it is effectively our smoking-gun proof that this is a black hole,” Reines said.
The role that black holes play in the universe is one of the biggest puzzles in astronomy, and the more data comes in, the more it’s starting to look like this is not a straightforward role, but rather a complex one. For instance, it was just recently demonstrated that researchers realized that most (if not all) galaxies have a black hole at their center. The more massive the galaxy, the more massive the central black hole — or possibly, the other way around, and the mass of the black hole is affecting the galaxy.
But we don’t really know how these central black holes (often called supermassive black holes) formed. Some researchers suspect they formed like “regular” black holes and somehow accumulated more and more mass; others believe they could only have formed in special conditions in the early stages of the universe; a further competing theory claims that the “seeds” of these black holes come from dense star clusters that collapse gravitationally. The black hole in Henize 2-10 could offer clues about these theories.
The black hole in the galaxy remained relatively small over cosmic time and did not accumulate a lot of material. This would suggest that it’s relatively unchanged since its formation, essentially offering a window into the early days of the universe.
“The era of the first black holes is not something that we have been able to see, so it really has become the big question: where did they come from? Dwarf galaxies may retain some memory of the black hole seeding scenario that has otherwise been lost to time and space,” Reines concludes.
An international team of astronomers reports on a new sighting of fluorine in another galaxy. This is the farthest the element has ever been detected and will help us better understand the stellar processes that lead to its creation.
Fluorine is the lightest chemical element in the halogen group, which it shares with other gases such as chlorine. It’s a very reactive element, and in our bodies, it helps give our bones and teeth mechanical strength as fluoride.
New research is helping us understand how this element is formed inside stellar bodies. The study also marks the farthest this element has ever been detected from our galaxy.
From stars to pearly whites
“We all know about fluorine because the toothpaste we use every day contains it in the form of fluoride,” says Maximilien Franco from the University of Hertfordshire in the UK, who led the new study.
“We have shown that Wolf–Rayet stars, which are among the most massive stars known and can explode violently as they reach the end of their lives, help us, in a way, to maintain good dental health!” he adds, jokingly.
The findings were made possible by a joint effort between the Atacama Large Millimeter/submillimeter Array (ALMA) and the European Southern Observatory (ESO), and pertain to a galaxy that’s 12 billion light-years away. The team identified fluorine in the form of hydrogen fluoride as large clouds of gas in the galaxy NGP-190387.
Due to the distance between Earth and NGP-190387, we still see it as it was at only 1.4 billion years old, around one-tenth of the estimated age of the Universe.
Like most of the chemical elements known to us, fluoride forms inside active stars. However, until now, we didn’t know the details of this process, or which stars produced the majority of the fluorine in the Universe.
This discovery helps us better understand how fluorine forms because stars expel chemical elements from their core near to or during the end of their lives. Due to the young age we perceive this galaxy as having from Earth, we can infer that the stars which formed the clouds of hydrogen fluoride must have appeared and died quickly in the grand scheme of things.
Wolf-Rayet stars, very large stellar bodies that only live for a few million years, are the main candidate that the team is considering. They fit the criteria of having short lives, and their size would allow for the huge quantities of hydrogen gas spotted in NGP-190387. Plus, it fits with our previous theories — Wolf-Rayet stars have been suggested as an important source of fluorine in the past, but we didn’t have enough data to confirm this theory, nor did we know how important they were for this process.
Although other processes have been suggested as likely sources of cosmic fluorine, the team believes that they couldn’t account for the time frame involved, nor for the sheer quantity of the element in NGP-190387.
“For this galaxy, it took just tens or hundreds of millions of years to have fluorine levels comparable to those found in stars in the Milky Way, which is 13.5 billion years old. This was a totally unexpected result,” says Chiaki Kobayashi, a professor at the University of Hertfordshire and co-author of the paper. “Our measurement adds a completely new constraint on the origin of fluorine, which has been studied for two decades.”
This is also the first time fluoride has been identified in such a far-away, star-forming galaxy. Since the distances involved in studying the Universe also mean that the further you look, the further back in time you see, it’s also the youngest star-forming galaxy we’ve ever detected fluoride in.
The paper “The ramp-up of interstellar medium enrichment at z > 4” has been published in the journal Nature Astronomy.
Ever wondered what a black hole sounds like? Well, if we’re being honest, it probably sounds like becoming a spaghetti and death, which are not very nice things. Understanding our pain, however, NASA comes with its most recent instalments of its sonification series, helping us hear space, but in a pleasant way.
You might be wondering what sonification is; in essence, it’s a process through which NASA turns astronomical data in the form of images into sounds. The data comes from NASA’s telescopes, such as the Chandra X-ray Observatory. Such images are then processed into sounds using an algorithm that, crucially, doesn’t change the original content of this data in any way. You could think of it like listening to an audiobook instead of reading it yourself.
The results are quite enjoyable, and surprisingly striking.
You can hear space in this
The first is a sonification of an image of the Chandra Deep Field South region of space. The image itself is notable as it is “the deepest image ever taken in X-rays” according to NASA, and represents “over seven million seconds of Chandra observing time”.
The colored dots that might seem like stars here are, in fact, individual galaxies and black holes — mostly supermassive ones. The colors of these individual dots dictate the tone produced as the bar moves throughout the picture from the bottom towards the top. White light on the picture is recreated as white noise, and the musical frequencies you’ll hear are given by different X-ray frequencies captured in the photo. In the image you see, these had to be heavily compressed but are shown in red, green, and blue for low, medium, and high-energy X-rays, respectively. However, keep in mind that the sound you’ll hear recreates the whole, uncompressed spectrum. Finally, the seter position of the sound tells you whether the source of light being sonified lies to the left or right of the image.
Next, the Cat’s Eye Nebula. This was formed by a star that’s slowly running out of atomic fuel (helium), which makes it belch out huge quantities of gas and dust. These form spectacular clouds that linger around the star.
The image used here contained both X-ray data around the center, recorded by Chandra, and visible light data from the Hubble Space Telescope, mostly focused on the structures expelled by the star.
Instead of a bar scanning the picture from bottom to top, here NASA uses a clockwise scan — it looks a lot like those radar lines you’d see in 90s action movies. When this line encounters light, pitch is produced: the farther away from the center it is, the higher the pitch. Brighter lights are also louder. X-ray data is reproduced in harsher notes while visible lights sound smoother.
It’s a very immersive tune.
The last installment in NASA’s sonification gallery is Messier 51, also known as the Whirlpool Galaxy, a spiral galaxy quite similar to our own.
The sonification moves radially from the top of the image in a clockwise motion. This time, the radius of the galaxy produces different notes on a minor scale. Each type of light (infrared, optical, ultraviolet, and X-ray) is represented here. The sound is… very eerie. Pleasant, but eerie. A constant, low hum is produced by the bright core of the galaxy, while other sources of light along its diameter produce short, striking sounds that almost sound coherent. I like this one the most out of all three, it’s just brimming with personality.
These three sonification projects were led by Dr. Kimberly Arcand, a visualization scientist at the Chandra X-ray Center (CXC), with astrophysicist Dr. Matt Russo and musician Andrew Santaguida (both of the SYSTEM Sound project).
If you liked these as much as I did, you’ll be delighted to hear that NASA has a whole gallery of sonification projects you can browse through, and listen to all of them here.
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.
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.
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.
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.”
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.”
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.
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.”
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.
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, .
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, , https://doi.org/10.1093/mnras/stz866
Our home galaxy, the Milky Way, contains a halo that consists of a hazy fog of dust, gas, and dark matter. Scientists already believe the enormous halo to measure at least 300,000 light-years across (as a reference point, the Milky Way itself reaches 100,000 light-years across space).
Now, a new study out of Ohio State University (OSU) suggests that the extreme temperatures the researchers found in a previous OSU analysis — up to 10 million degrees Kelvin, or about 18 million degrees Fahrenheit — could possibly be found throughout the whole halo. Prior it was believed that only certain parts of the halo could reach the high temperature.
“We can’t say for sure that it is everywhere, because we have not analyzed the entire halo,” said Smita Mathur, professor of astronomy at OSU. “But we know now that the temperatures we saw in the first study definitely are not unique, and that is very exciting.”
A recent April study out of the University of California, Irvine found that the Milky Way could be flinging stars into the outer halo. The movements are believed to be triggered by powerful supernova explosions. Supernovas occur when stars explode and lose most of their mass.
“These highly accurate numerical simulations have shown us that it’s likely the Milky Way has been launching stars in circumgalactic space in outflows triggered by supernova explosions,” study author James Bullock, dean of the university’s School of Physical Sciences and a professor of physics and astronomy. “It’s fascinating, because when multiple big stars die, the resulting energy can expel gas from the galaxy, which in turn cools, causing new stars to be born.”
The data from the Ohio State report came from an X-ray observatory telescope run by the European Space Agency. That telescope, called XMM-Newton, collects data in X-rays that would have otherwise been blocked by Earth’s atmosphere.
“It showed us that the halo was much hotter than we had known, but it didn’t show us whether that was the case throughout the galaxy, or if the telescope had picked up an aberration caused by an unknown force coming from the direction where the telescope was pointed,” Mathur said.
Anjali Gupta, a visiting astronomy researcher at OSU, analyzed data from Suzaku, a Japanese X-ray satellite telescope, which collected spectrum data from the Milky Way’s halo in four different directions. That analysis confirmed their earlier findings — that the halo is much hotter than had previously been known.
However, it still remains to be seen if the same conditions exist for halos surrounding those galaxies far, far, away.
The new findings were presented at the annual meeting of the American Astronomical Society, held online this week because of the COVID-19 pandemic.
Although things are getting pretty stressful here on Earth, it’s worth remembering that the universe is still an amazing place. A new image of the galaxy NGC 4651 captured by the Hubble Space Telescope is a great way to remind us of that.
NGC 4651 sprawls about 93 million light-years away from our home, in the constellation of Coma Berenices — Latin for “Berenice’s Hair”. This group of stars is visible from both hemispheres and is the only constellation to be named after a historical figure.
The galaxy was first discovered by the German-born British astronomer William Herschel on December 30, 1783. But it hasn’t been seen in such exquisite detail ever before.
Pretty but dangerous
“NGC 4651 may look serene and peaceful as it swirls in the vast, silent emptiness of space, but don’t be fooled — it keeps a violent secret,” the Hubble team said. “It is believed that this galaxy consumed another smaller galaxy to become the large and beautiful spiral that we observe today.”
NGC 4651 is also known as the Umbrella Galaxy for the umbrella-like structure that extends some 100 thousand light-years beyond its disk. This bright structure is composed of tidal star streams — trails of starstuff that the galaxy’s gravitational pull stripped from a smaller satellite galaxy. This smaller galaxy has been completely devoured by NGC 4651 by this point.
The team explains that this galaxy can be seen even with “an amateur telescope,” so if you do happen to have one on hand, that could help make your quarantine just a bit more bearable.
In a galaxy far, far away… astronomers have discovered the most massive black hole in the local observable universe. According to recent observations, the black hole at the center of the Holm 15A galaxy has a staggering 40 billion solar masses. For comparison, the Milky Way’s supermassive black hole measures only 4 million solar masses.
The discovery came to light while a team of astronomers, from the Max Planck Institute for Extraterrestrial Physics and the University Observatory Munich, was surveying Abell 85. It is a galaxy cluster located about 740 million light-years from Earth, which consists of more than 500 individual galaxies.
Holm 15A came to the researchers’ attention when they noticed a huge dark patch at its center. For a galaxy whose stars are equivalent to 2 trillion solar masses — in other words, a very bright galaxy — this was highly surprising to see.
Observations suggested that the murky and diffuse center of Holm 15A is almost as large as the Large Magellanic Cloud, a big clue hinting towards the presence of a black hole with a very high mass.
“There are only a few dozen direct mass measurements of supermassive black holes, and never before has it been attempted at such a distance,” said Jens Thomas, a Max Planck researcher and the lead author of the study. “But we already had some idea of the size of the Black Hole in this particular galaxy, so we tried it.”
With the help of the observatory at the University Observatory Munich and the MUSE instrument at the Very Large Telescope in Chile, the astronomers were able to estimate the black hole’s mass by measuring the motion of stars around the galaxy’s core. The results suggest that at the heart of Holm 15A lies a behemoth with 40 billion solar masses — the most massive black hole yet known to scientists in the local universe.
“This is several times larger than expected from indirect measurements, such as the stellar mass or the velocity dispersion of the galaxy,” says Roberto Saglia, senior scientist at the Max Planck Institute for Extraterrestrial Physics.
The diffuse galactic core also suggests that Holm 15A formed after two smaller galaxies merged. Both had supermassive black holes at their center, so when the galaxies merged, so did the black holes. As the black hole became more massive, so did the rate at which stars were expelled from the center due to the gravitational interactions between the merging elements, a physical process known as core-scouring. And, because there is no gas left in the galactic core to form new stars, it will look depleted, dim, and diffuse.
“The newest generation of computer simulations of galaxy mergers gave us predictions that do indeed match the observed properties rather well,” Thomas said. “These simulations include interactions between stars and a black hole binary, but the crucial ingredient is two elliptical galaxies that already have depleted cores. This means that the shape of the light profile and the trajectories of the stars contain valuable archaeological information about the specific circumstances of core formation in this galaxy—as well as other very massive galaxies.”
The study’s key insight lies in the newly established relationship between black hole mass and a galaxy’s surface brightness. In the future, astronomers could use this insight to estimate a black hole’s mass in more distant galaxies where our instruments are unable to measure stellar motions in the vicinity of a galactic core.
How did the universe evolve from a point of singularity, known as the Big Bang, into a massive structure whose boundaries seem limitless? New clues and insight into the evolution of the universe have recently been provided by an international team of physicists, who performed the most detailed large-scale simulation of the universe to date.
The researchers made their own universe in a box — a cube of space spanning more than 230 million light-years across. Previous cosmological simulations were either very detailed but spanned a small volume or less detailed across large volumes. The new simulation, known as TNG50, managed to combine the best of two worlds, producing a large-scale replica of the cosmos while, at the same time, allowing for unprecedented computational resolution.
The level of detail is incredible, matching what was once only possible to do in simulations of individual galaxies. TNG50, in fact, tracks 20 billion particles representing dark matter, stars, cosmic gas, magnetic fields, and supermassive black holes.
However, this kind of fine detail came at a cost. It took more than 16,000 cores on the Hazel Hen supercomputer in Stuttgart operating in tandem, non-stop for a year to perform the required calculations. For reference, it would have taken 15,000 years to complete the simulation on a single processor, making TNG50 one of the most computationally demanding astrophysical simulations to date.
In two recently published studies led by Annalisa Pillepich and Dylan Nelson, from the Max Planck Institute for Astronomy and Max Planck Institute for Astrophysics, respectively, the researchers shared their most important findings.
“Numerical experiments of this kind are particularly successful when you get out more than you put in. In our simulation, we see phenomena that had not been programmed explicitly into the simulation code. These phenomena emerge in a natural fashion, from the complex interplay of the basic physical ingredients of our model universe,” Nelson said in a statement.
One example of such emerging behavior if the formation of “disk” galaxies, like the Milky Way. While disk galaxies seem very ordered and flat, by rewinding their evolution, researchers could see that such structures emerge from chaotic and disorganized turbulent clouds of gas.
“In practice, TNG50 shows that our own Milky Way galaxy with its thin disk is at the height of galaxy fashion: over the past 10 billion years, at least those galaxies that are still forming new stars have become more and more disk-like, and their chaotic internal motions have decreased considerably. The Universe was much more messy when it was just a few billion years old!” Pillepich said in a statement.
Another emerging phenomenon captured by the simulation was represented by high-speed outflows and winds of gas emanating from galaxies. These outflows and winds are the result of supernovae and supermassive black hole activity.
These galactic outflows were initially chaotic — just like early galactic structures — but, over time, they became more focused on the paths of least resistance. In the modern universe, these winds slow down as they make their way away from the gravitational well of the dark matter halo, and can eventually stall and fall back onto their parent galaxies. The astronomers liken the process to a galactic fountain of recycled gas.
By this process, gas is redistributed from the center of the galaxy to its outskirts. In time, this contributes to the transformation of the galaxy into a thin disk. But this can also work both ways: galactic structures also shape galactic fountains.
In the future, the astronomers will release all the simulation’s data to the scientific community at large so that new discoveries might come out of the TNG50 universe.
A cleverly designed experiment takes us one step closer to a fundamental truth — but there’s still a long way to go.
When something is called “dark energy”, it’s bound to be mysterious and weird, but dark energy is really weird. For starters, we don’t even know what is.
It seems counterintuitive, but our universe is expanding. Not only is it expanding, but this expansion is also accelerating — which seems really bizarre, as you’d expect gravity to slowly clump things closer together. Dark energy is believed to be the reason behind this acceleration.
It seems to permeate all the space in the universe and it’s very homogenous, but it only interacts with the gravitational force and is extremely rarefied, which makes it extremely difficult to study and analyze. This leaves the question “so what is it” very much on the table, with no satisfying answer.
Some physicists have proposed that dark energy is a fifth fundamental force — adding to the well-known gravity, electromagnetic, weak nuclear and strong nuclear forces. This hypothesis has been put to the test by researchers at Imperial College London and the University of Nottingham.
If this were the case and dark energy was a force, you’d expect it to be some sort of repulsive force, something that makes the universe “larger“. To test this, the experiment worked on single atoms, using a device called an atom interferometer. This detects any extra force which might be acting on the atom. The experimental setup featured a small metal sphere placed in a vacuum chamber, with atoms freefalling through the chamber.
In theory, if dark energy was a fifth force, it would be weaker when there is more matter around. So in this design, the freefalling atoms would change paths ever so slightly as they passed by the sphere. However, this turned out to not be the case. The atoms continued unabated as they passed the sphere, essentially ruling out the idea that dark energy is a fundamental force.
This does more than just rule out one possibility — it helps constrain the cosmological models attempting to describe dark energy. Professor Ed Copeland, from the Centre for Astronomy & Particle Physics at the University of Nottingham, explains:
“This experiment, connecting atomic physics and cosmology, has allowed us to rule out a wide class of models that have been proposed to explain the nature of dark energy, and will enable us to constrain many more dark energy models.”
The fact that this experiment is relatively simple but helps to reveal one of the fundamental truths of the universe makes it all the more remarkable, researchers say.
“It is very exciting to be able to discover something about the evolution of the universe using a table-top experiment in a London basement,” said Professor Ed Hinds of the Department of Physics at Imperial.
Four billion years from now, the Milky Way and Andromeda galaxies will collide in an epic clash of the titans that will light the sky in other worlds that are far away enough from the mayhem. This wouldn’t be the first time our galaxy is involved in a galactic merger. According to astronomers at the Instituto de Astrofisica de Canarias (IAC), about 10 billion years ago the Milky Way devoured a dwarf galaxy called Gaia-Enceladus. The remnants of the dwarf galaxy are believed to now form the Milky Way’s famous halo.
Big fish get bigger
Astronomers used to believe that the Milky Way is formed of two separate sets of stars. The disparities between some stars eventually turned out to reflect a much more complex story. Spanish researchers at IAC used the Gaia space telescope to measure the position, brightness, and distance of roughly one million stars. The research team also analyzed the density of metals found in stars, which revealed the disparities between the two sets — one “bluer” containing less metal, one “redder” containing more.
Remarkably, the researchers found that both sets of stars are about the same age only that the “blue” one was set into a “chaotic motion” — a telltale sign of a violent galactic collision.
“The novelty of our work is that we have been able to assign precise ages to the stars that belong to the galaxies that merged and, by knowing these ages, when the merger took place,” Carme Gallart, lead author of the study published in Nature Astronomy, said in a statement.
The Milky Way is made of at least 100 billion stars, held together by the immense gravity of a supermassive black hole lying at its center, called Sagittarius A*. The astronomers say that the collision between proto-Milky Way and Gaia-Enceladus promoted star formation for four billion years, after which gas from these formations settled into the Milky Way’s thin disk while remnants of the dwarf galaxy formed our galaxy’s halo.
It’s quite impressive that scientists were able to identify the very first stars that were part of the early Milky Way and how our galaxy was modified by this merger. Studies such as this will not only inform scientists how the Milky Way formed but also how galaxies evolve in general.
This deep-field view of the sky (center) taken by NASA’s Hubble and Spitzer space telescopes is dominated by galaxies – including some very faint, very distant ones – circled in red. The bottom right inset shows the light collected from one of those galaxies during a long-duration observation. Image credits: NASA/JPL-Caltech/ESA/Spitzer/P. Oesch/S. De Barros/I.Labbe
For all its mind-bending features, the universe is a pretty ordered place. Stars and planets are neatly arranged into solar systems; solar systems have vast swaths of space between them and are themselves arranged into galaxies. Space is also transparent and decently lit by stars, which is nice because it allows us to see at large distances, and, because of how light works, also allows us to see in the past.
But it wasn’t always like this. In its earlier days, the universe was much more tumultuous. For the first 377,000 years, it was a soup of various types of matter and antimatter, finally becoming cool enough for individual atoms to form — but it was still dark and murky. Even some 1 billion years after the Big Bang, when the universe had become transparent, there weren’t too many sources of light because it takes such a long time for mass to collapse into stars and galaxies, though light had been sparked nonetheless.
Here’s the thing, though: while Dark Ages of the universe started around 377,000 years after the Big Bang, there was still some radiation. Something started exciting the hydrogen with radiation, ionizing it and producing light. Astronomers are not really sure how this happened, though.
No one really knows when the first stars in the universe came to be. There is evidence suggesting that they formed some 100-200 million years after the Big Bang — but did they have enough energy to produce this ionization phenomenon? That’s hard to say.
Now, a new study finally sheds some light on this issue.
“It’s one of the biggest open questions in observational cosmology,” said astronomer Stephane De Barros of the University of Geneva. “We know it happened, but what caused it? These new findings could be a big clue.”
In an attempt to answer this question, De Barros and colleagues directed the Spitzer telescope at two separate regions of the night sky. The telescope detected 135 galaxies that formed just 730 million years after the Big Bang, and they were very different from the galaxies we’re used to seeing.
For starters, they were very bright in two specific wavelengths of infrared light produced by ionizing radiation interacting with hydrogen and oxygen gases within the galaxies. This suggests that the galaxies were dominated by hydrogen and helium, containing very small amounts of “heavy” elements (like nitrogen, carbon and oxygen) compared to stars found in average modern galaxies. But the most surprising (and important) finding was that they were so bright — much brighter than researchers anticipated.
This suggests that average galaxies at the time were much brighter than average galaxies are now.
It’s the first study to document the brightness of galaxies from this period. Although these galaxies were not the first generation, they are still a very old group which could shed new light on this reionization era, a key process of the evolution of the universe.
The fact that these observations could even be made with Spitzer was surprising, researchers say.
“We did not expect that Spitzer, with a mirror no larger than a Hula-Hoop, would be capable of seeing galaxies so close to the dawn of time,” said Michael Werner, Spitzer’s project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “But nature is full of surprises, and the unexpected brightness of these early galaxies, together with Spitzer’s superb performance, puts them within range of our small but powerful observatory.”
“These results by Spitzer are certainly another step in solving the mystery of cosmic reionization,” said Pascal Oesch, an assistant professor at the University of Geneva and a co-author on the study. He also adds that the James Webb telescope, which is set to launch in 2021, will study these stars with a mirror 7.5 largers than Spitzer’s. “We now know that the physical conditions in these early galaxies were very different than in typical galaxies today. It will be the job of the James Webb Space Telescope to work out the detailed reasons why.”
For thousands of years, humans thought that Earth was at the center of the universe. It was only in recent centuries that it became an established scientific fact that Earth orbits the sun, and later that the solar system — along with hundreds of billions of other stars — orbits a common galactic center. Until very recently, it has been very difficult for scientists to visualize what the Milky Way looks like given that we are embedded inside it.
Artist impression of a warped Milky Way. Credit: CHEN Xiaodian.
Thanks to observation, reconstruction, and comparison to other galaxies, researchers have a fairly accurate idea of what our galaxy looks like. If you were to travel outside the galaxy and look down upon it from above, what you’d see is a barred spiral galaxy with two spiral arms called Scutum–Centaurus and Carina–Sagittarius. But, the spiral disk is anything but stable, new research from China shows. The new study found that the farther away you travel from the galactic core, this disk becomes increasingly warped and twisted.
The Milky Way’s S-like appearance at its edges is due to the fact that gravity becomes weaker the farther you are from the galaxy’s inner regions. Since hydrogen atoms in the far outer disk are no longer confined to a thin plane, they get warped.
There were many challenges in this study. One of them is establishing distances from the sun to the Milky Way’s outer disk when you don’t know what the disk actually looks like yet. The research team at the National Astronomical Observatories of Chinese Academy of Sciences (NAOC), led by Chen Xiaodian, had to employ a new catalog of variable stars known as classical Cepheids. Such stars are hot and massive – five to twenty times the mass of our sun and up to 100,000 times as bright. They also pulsate radially for days to months at a time — and this period of pulsation can be combined with the Cepheid’s brightness to reliably establish its distance from the sun.
A 3D distribution of the classical Cepheids in the Milky Way’s warped disk. Credit: CHEN Xiaodian.
Because they are so bright, Cepheids can be clearly seen millions of light years away and can be easily distinguished from other bright stars in their vicinity, making them indispensable tools in any astronomers’ kit. For instance, it’s thanks to Cepheids that Edwin Hubble and Milton L. Humason were able to prove that the Universe is in a state of expansion. Now, Cepheids have proven their worth once more, establishing an important physical characteristic of the Milky Way’s disk.
“Somewhat to our surprise, we found that in 3D our collection of 1339 Cepheid stars and the Milky Way’s gas disk follow each other closely. This offers new insights into the formation of our home galaxy,” says Prof. Richard de Grijs from Macquarie University in Sydney, Australia, and senior co-author of the paper. “Perhaps more importantly, in the Milky Way’s outer regions, we found that the S-like stellar disk is warped in a progressively twisted spiral pattern.”
The same twisted spiral patterns have been seen before in more than a dozen other galaxies. Combined with these observations, the study’s results suggest that the likely culprit for the Milky Way’s warped spiral pattern is torque from the massive inner disk.
“This new morphology provides a crucial updated map for studies of our galaxy’s stellar motions and the origins of the Milky Way’s disk,” says Dr. DENG Licai, senior researcher at NAOC and co-author of the study published in Nature Astronomy.
Some of the oldest galaxies in the universe are right in front of our doorstep — cosmically speaking.
The blue circles surround brighter galactic satellites, the white circles ultrafaint satellites (so faint that they are not readily visible in the image). Ultrafaint satellites are amongst the most ancient galaxies in the Universe, beginning to form when the Universe was only about 100 million years old (compared to its current age of 13.8 billion years). The image has been generated from simulations from the Auriga project. Image credits: Institute for Computational Cosmology, Durham University, UK / Heidelberg Institute for Theoretical Studies, Germany / Max Planck Institute for Astrophysics, Germany.
The universe dark ages
Some 13.8 billion years ago (give or take), something pretty weird happened: the Universe started existing. According to the Big Bang theory, the universe formed out of a point of infinite density and temperature. In the immediate second after the Big Bang, a whole bunch of weird processes started taking place. The four fundamental forces started taking hold but the temperature of the universe was still too high to allow the formation of particles.
Then, after around 377,000 years, the universe had cooled to a point where free electrons could combine with the hydrogen and helium nuclei to form neutral atoms. This is where it gets tricky: although the universe had cooled down and was essentially transparent, nothing that could produce light had yet formed. There were no stars, no galaxies, maybe some primordial black holes and other structures — but no light. The universe was dark and essentially unobservable.
This is the so-called Dark Age of the universe.
[panel style=”panel-info” title=”Looking back in time” footer=””] Observing a faraway cosmic object is like looking back in time. For instance, when something is 1 million light years away, we’re perceiving it as it was 1 million years ago — because that’s how long it took light from it to get to us.
But because in its opaque form there were no light-producing structures, we can’t look back to that period of time. It simply remains hidden to us — at least as far as visible light is concerned. [/panel]
Eventually, stars and galaxies started forming — and some of these early galaxies were recently discovered by British astronomers.
Our old neighbors
Image of a galaxy generated from simulations from the Auriga project. Credit: Institute for Computational Cosmology, Durham University, UK / Heidelberg Institute for Theoretical Studies, Germany / Max Planck Institute for Astrophysics, Germany.
The research team has found evidence that the faintest satellite galaxies orbiting our own Milky Way galaxy are amongst the very first galaxies to form in our Universe. The galaxies they identified were likely formed more than 13 billion years ago — right after the Dark Ages settled in.
“Finding some of the very first galaxies that formed in our Universe orbiting in the Milky Way’s own backyard is the astronomical equivalent of finding the remains of the first humans that inhabited the Earth. It is hugely exciting.”
If their findings are confirmed, that would mean that the galaxies emerged just 380,000 years after the Big Bang, which means they formed by some of the first atoms in the universe.
Remarkably, the data fitted perfectly with a model of galaxy formation that the team had previously developed — the model essentially allowed them to infer the formation times of the satellite galaxies, and now, observation has confirmed the model.
“Our finding supports the current model for the evolution of our Universe, the ‘Lambda-cold-dark-matter model’ in which the elementary particles that make up the dark matter drive cosmic evolution,” Frenk adds.
It’s always exciting when theoretical and real data blend in so well together and, as Dr. Sownak Bose points out, we simply wouldn’t have had the technological capacity to carry out this study a decade or two ago. Bose, who was a Ph.D. student at the ICC when this work began and is now a research fellow at the Harvard-Smithsonian Center for Astrophysics, concluded:
“A decade ago, the faintest galaxies in the vicinity of the Milky Way would have gone under the radar. With the increasing sensitivity of present and future galaxy censuses, a whole new trove of the tiniest galaxies has come into the light, allowing us to test theoretical models in new regimes.”
The work was carried out as part of the Auriga project — a large suite of high-resolution simulations of Milky Way-sized galaxies, simulated in a fully cosmological environment by means of the ‘zoom-in’ technique. Read more about Auriga here.
Journal Reference: Sownak Bose, Alis J. Deason, and Carlos S. Frenk. “The Imprint of Cosmic Reionization on the Luminosity Function of Galaxies,” The Astronomical Journal.
Our closest galactic neighbor, Andromeda, seems to like the taste of its brethren.
The Andromeda Galaxy imaged through a hydrogen-alpha filter. Image credits Adam Evans.
Researchers from the University of Michigan (UoM) report that the Andromeda galaxy smote and consumed one of its brethren some two billion years ago. Although its victim was shredded almost completely, the team pieced together evidence of the collision from the thin halo of stars that spans the gap between Andromeda and its enigmatic companion, Meiser 32 (M32).
The discovery helps further our understanding of how galaxies like the Milky Way evolve, and of their behavior during large mergers.
Our own galaxy, the Milky Way, and our closest neighbor, Andromeda, are the two largest members of a group known as the Local Group (of galaxies). The extended family includes some 54 different galaxies — most of them dwarf galaxies acting as satellites for their larger relatives — all orbiting around a point roughly between Andromeda and the Milky Way.
It may sound idyllic, but researchers have found that at least one member of this group found its demise at the hands of Andromeda. This once-galaxy, christened M32p, was the third-largest member of the Local Group — a distinction that now falls on the galaxy Triangulum.
The team started their research using data pertaining to the halo of stars around Andromeda. It’s not a unique feature; many galaxies harbor such wispy-thin groupings of stars around their bulk, the final remnants of smaller galaxies that they absorbed over time. Since Andromeda is so large and rich in matter (it has over double the diameter of the Milky Way and double its number of stars), the researchers expected it to have consumed hundreds of smaller galaxies — which they thought would make it impossible to study a single such meal.
Size comparison between M32p and today’s M32. Image credits Richard D’Souza; for the image of M64: NOAO/AURA/NSF.
However, the team’s computer simulations revealed that although Andromeda did dine on many of its companion galaxies, most stars in the outer halo originate from a single, large galaxy. Piecing the evidence together to peer back in time, the team found that M32p would have been massive — likely the third-largest in the Local Group, after Andromeda and the Milky Way. The paper adds that M32p was at least 20 times larger than any galaxy the Milky Way ever merged with.
“The stars in Andromeda are very metal-rich and considerably young,” Richard D’Souza, lead author of the paper, explained in an e-mail. “In general, the larger the galaxy the more metal rich the stars are. We suspected that since the stars in the halo of Andromeda were so metal-rich, it must have come from a large metal-rich galaxy.”
One big bite
A metal-rich halo large enough to encompass a galaxy such as Andromeda could only be formed “through a single large merger,” he adds, noting that “there are not many smaller galaxies in the Universe to build up to the mass of the halo”.
“In terms of a business analogy, galaxies also grow through mergers and acquisitions. In order for a major company to grow at a very fast pace, it would need to acquire a similar large company into its business. Such was the case with Andromeda,” D’Souza adds.
The findings call into question our models of how mergers between two massive galaxies play out. Until now, astronomers believed that such an event would flatten the disk of a spiral galaxy into an elliptical one, but Andromeda’s disk evidently pulled through still very spiral-shaped. Some effects of this collision can still be seen, D’Souza told me. Among them are the thickness of Andromeda’s disk and the higher speeds its stars travel at (90 km/s compared to around 30 km/s in the Milky Way).
The process of shredding of the large galaxy M32p by the Andromeda (M31) galaxy which eventually resulted in M32 and a giant halo of stars. Image credits Richard D’Souza; M31, courtesy of Wei-Hao Wang; Stellar halo of M31: AAS/IOP.
Still, he admits that it came as “a major surprise” that Andromeda could retain its spiral shape following this collision. One explanation could be that the particular angle of the collision between the two galaxies helped keep Andromeda spiral-like, “but we need to run more computer simulations to see which set of orbits helps preserve the disk”.
Beyond this, it helps us better understand Andromeda’s evolution over time. The timing of the merger coincides with a burst of intense star formation in Andromeda two billion years ago. All this star-forming activity also suggests that M32p must have been gas-rich in order to supply enough building blocks.
Finally, the findings point to Andromeda’s mysterious, compact, and very dense, satellite galaxy M32 (the one today) as the last sliver of the once-mighty galaxy — the naked core. This piece of data could help explain why we see so few galaxies similar to M32 zipping around in the universe.
“M32 is a weirdo,” co-author Eric Bell, UoM professor of astronomy, said in a press release. “While it looks like a compact example of an old, elliptical galaxy, it actually has lots of young stars. It’s one of the most compact galaxies in the universe. There isn’t another galaxy like it.”
“Galaxies like M32 are considerably rare in the Universe,” D’Souza adds. “The term used for them in the literature is called ‘compact ellipticals’, and they are one of the most rarest galaxies in the Universe. We do know a dozen or so compact ellipticals in the nearby Universe, and we have inferred that further out (where we cannot resolve them), the number is equally low.”
As part of the paper, the team also found that the merger scenario could help explain the scarcity of M32-like objects. It seems the secret is not just in the merging process itself, but also in the particular makeup of the galaxies involved. “What one really needs is a galaxy with a high central surface density of stars comparable to M32,” D’Souza explains. It seems to be quite a rare occurrence — the team only identified 8 potential progenitors for M32-like objects.
Their study may alter the traditional understanding of how galaxies evolve, the researchers say. The realization that Andromeda’s disk survived an impact with a massive galaxy flies in the face of our current models, which suggests that such large interactions would destroy disks and form an elliptical galaxy.
It went so fundamentally against the grain of our understanding of galaxy-formation that, previously, we didn’t even consider the possibility that this scenario could have ever occurred.
“Astronomers have been studying the Local Group–the Milky Way, Andromeda and their companions–for so long. It was shocking to realize that the Milky Way had a large sibling, and we never knew about it,” Bell concludes.
Such investigative methods can be applied to other galaxies as well, the team explains, to help us tease out the merger history of other galaxies besides Andromeda.
The paper “The Andromeda galaxy’s most important merger about 2 billion years ago as M32’s likely progenitor” has been published in the journal Nature Astronomy.
It’s impossible to know for sure, but Hubble revealed that there are at least 100 billion galaxies in the universe. However, this may be a conservative estimation — other estimates put the total number of galaxies at 2 trillion.
These are all galaxies, so here goes: one, two, three… Image credits: Hubble.
What is a galaxy
Before we start looking for galaxies and counting them, we need to know just what a galaxy is.
Essentially, a galaxy is a huge collection of gas, dust, and billions of stars all tied together by gravity. Although the distances between stars within the same galaxy can be huge, it’s important that they’re all connected into a single cluster by gravity — that’s what makes it a galaxy. Most galaxies have a supermassive black hole at their center, which helps keep it all together. As the name implies, supermassive black holes are immensely massive black holes — they have a mass on the order of millions or even billions of solar masses.
There are three types of galaxies: elliptical, spiral, and irregular. The name pretty much describes the overall shape of the galaxy: elliptical galaxies look like an “egg” of light (an ellipse), spiral galaxies extend arms around the central bulge, and irregular galaxies are pretty much everything that’s not spiral or elliptical. The Milky Way, our own galaxy, is a spiral galaxy. It seems strange that complex and diverse systems such as galaxies take on such few shapes. Researchers are still not exactly sure why this happens, but these common shapes are likely the product of rotation speed, time and gravity.
The Pinwheel Galaxy, NGC 5457. A classic spiral galaxy. Image credits: Hubble.
Galaxies can also vary greatly in size, which means that some are more easily visible than others. Dwarf galaxies have between 100 million and several billion stars (a very small number compared to the Milky Way’s 200-400 billion stars), measuring “only” 300 light-years. Meanwhile, “IC 1101” is the single largest galaxy that has ever been found in the observable universe, spanning a whopping 210,000 light-years across.
Looking for galaxies
So how does one look for galaxies? We can all see (on clear nights) the bright, milk-ish band that lends our galaxy its name. More than 2,000 years ago, the Greek philosopher Democritus (450–370 BCE) proposed that the band might consist of distant stars, a surprisingly insightful idea. Of course, there are many things that Democritus couldn’t have known, and it wasn’t until 1610 when the Italian astronomer Galileo Galilei used a telescope to study the Milky Way and discovered that it is composed of a huge number of faint and very distant stars.
Fast forwarding to modern times, telescopes have obviously gotten a lot better. But one of the biggest problems for all telescopes is the atmosphere, which contains a lot of light pollution and distortion of electromagnetic radiation. Thankfully, astronomers have by-passed that problem by building space telescopes — yes, we have telescopes in outer space. The most famous one, although not the first, is the Hubble telescope. Hubble is a vital research tool which has provided an invaluable trove of data. Among others, the landmark Hubble Deep Field, taken in the mid-1990s, gave the first real insight into the universe’s galaxy population.
The Antennae Galaxies, featured here, will eventually merge. Image credits: Hubble.
But even with Hubble, counting galaxies is extremely difficult for the simple fact that the universe is, well, very big. Looking in all directions and counting all the galaxies is nigh impossible, so instead, astronomers just focus on a sector of the night sky, count the galaxies there, and extrapolate based on that value. Of course, this can lead to some inaccuracies, but given the sheer size of the universe and the number of galaxies, the inaccuracies are unlikely to be significant.
How many galaxies are there
So, back to the question: how many galaxies are there? The first measurements from the 1990s found that there are 200 billion galaxies in the universe. However, that figure is unlikely to be reliable. Subsequent sensitive observations found that many faint galaxies were not observed the first time. The most recent, and likely the most accurate, survey found that the real number of galaxies is ten times larger: so, in total, there are 2 trillion galaxies in the universe, or 2,000 billion, if you prefer.
In late 2016, Christopher Conselice, Professor of Astrophysics at the University of Nottingham, along with several colleagues, carried out a sort of archaeological cosmology: they calculated the density of galaxies as well as the volume of one small region of space after another. This painstaking research was the culmination of 15 years of research, and it enabled the team to establish how many galaxies we have missed. The team found that, initially, astronomers missed a lot of galaxies because they were faint and very far away.
“We are missing the vast majority of galaxies because they are very faint and far away. The number of galaxies in the universe is a fundamental question in astronomy, and it boggles the mind that over 90% of the galaxies in the cosmos have yet to be studied. Who knows what interesting properties we will find when we study these galaxies with the next generation of telescopes?”
Each light speck is a galaxy, some of which are as old as 13.2 billion years. The universe is estimated to contain anywhere between 200 billion and 2 trillion galaxies. Image credits: Hubble.
Since many of the very distant galaxies are also faint, it seems that the total number of galaxies is currently decreasing over time. However, the more important takeaway lesson here is that we’re still only seeing a very small portion of the universe. Who knows what we might be missing out on. The study also says that the real number of galaxies might be even higher — up to 10 trillion galaxies.
“It boggles the mind that over 90% of the galaxies in the universe have yet to be studied,” commented Conselice. “Who knows what interesting properties we will find when we observe these galaxies with the next generation of telescopes?” he said in a statement.
Bonus: How many planets are there in the Universe?
If you’re still trying to wrap your mind around the number of galaxies, here’s another one. Estimating how many planets there are in the universe is much more a ballpark figure, and relies much more on deduction than direct observation. But for the fun of it, let’s do some simple math. Let’s say there are 2 trillion galaxies out there. The Milky Way is a fairly average galaxy, and it has over 200 billion planets. If we extrapolate based on that, we end up with 400 billion trillion planets in the universe. That’s 400,000,000,000,000,000,000,000 planets.
Again, this is definitely an approximation and not scientifically accurate, but it’s something to consider when you feel like you’re pretty important.
Every once in a while, you’ll learn something that makes you feel overwhelmingly tiny and insignificant — this is one of those things.
An artist’s impression of the 14 colliding galaxies. NRAO / AUI / NSF / S. Dagnello.
A group of 14 galaxies that formed about 1.4 billion years after the Big Bang are bound to merge, resulting in an incredibly massive structure, possibly the largest in the Universe. But there’s a catch: this all happened a really, really long time ago, but we’re only seeing it now.
Whenever we look at something that’s extremely far away, we’re essentially looking back in time. When we’re observing something that’s, say, one million light years away from us, we’re observing it as it was one million years ago — because that’s how long it took for the light to reach us.
In this case, the galaxies are packed into an area only four times the diameter of the Milky Way’s galactic disk, some 12.4 billion light-years away from Earth — so we’re seeing how they were 12.4 billion years ago. At the time when we can observe them, they were merging into a galaxy cluster, a rare phenomenon which we’ve only rarely observed.
“More so than any other candidate discovered to date, this seems like we’re catching a cluster in the process of being assembled,” says study co-author Chris Hayward, an associate research scientist at the Center for Computational Astrophysics at the Flatiron Institute in New York City. “This is the missing link in our understanding of how clusters form.”
Astronomers report that the cluster must be incredibly dense to host that many stars and galaxies in such a (relatively) small space. It;’s like if you put all the planets in our solar system in the space between the Earth and the Moon, explains Dr. Axel Weiß, a co-author on the study.
Another artistic interpretation of the cluster. Image credits: ESO/M. Kornmesser.
The merging was originally detected in a wide sky survey using the South Pole Telescope. The objects surprised astronomers as they were closely packed together — they weren’t expecting something this spectacular. An additional study by the Atacama Large Millimeter/submillimeter Array in Chile provided clarity and revealed just what they had come across.
“It just hit you in the face because all of a sudden there are all these galaxies there,” says study co-author Scott Chapman, the Killam Professor in astrophysics at Dalhousie University in Halifax, Canada. “We went from three to 14 in one fell swoop. It instantly became obvious this was a very interesting, massive structure forming and not just a flash in the pan.”
All in all, the emerging cluster contains about 10 trillion suns’ worth of mass, and exhibits surprisingly high star formation rates: it churns out stars about 1,000 times faster than the Milky Way.
“There’s some special aspect of this environment that’s causing the galaxies to form stars much more rapidly than individual galaxies that aren’t in this special place,” says Hayward. One possible explanation is that the gravitational tug of neighboring galaxies compresses gas within a galaxy, triggering star formation.
So, what has the cluster been up to in the past 12.4 billion years? Well, astronomers believe this protocluster is a precursor to the larger and more mature galaxy clusters we’ve observed in more modern parts of the universe. By now, the cluster may very well look like the so-called Coma Cluster — a large cluster of galaxies that contains over 1,000 identified galaxies. By now, researchers say, the coalesced cluster may have grown to the mass of 1,000 trillion suns. If that’s not enough to make you feel incredibly small, then I don’t know what is.
Journal Reference:T. B. Miller et al. A massive core for a cluster of galaxies at a redshift of 4.3. Nature, 2018; 556 (7702): 469 DOI: 10.1038/s41586-018-0025-2
The map shows the total brightness and colour of stars observed by the ESA satellite in each portion of the sky between July 2014 and May 2016. Brighter regions indicate denser concentrations of especially bright stars, while darker regions correspond to patches of the sky where fewer bright stars are observed. Credit: Gaia Data Processing and Analysis Consortium (DPAC).
ESA’s Gaia mission has now released the richest star catalogue to date, accurately pinpointing the position of more than 1.7 billion stars. The painstaking work, which required more than 22 months of charting the sky, will enable astronomers to investigate the formation and evolution of the Milky Way in unprecedented detail.
“The observations collected by Gaia are redefining the foundations of astronomy,” says Günther Hasinger, ESA Director of Science.
“Gaia is an ambitious mission that relies on a huge human collaboration to make sense of a large volume of highly complex data. It demonstrates the need for long-term projects to guarantee progress in space science and technology and to implement even more daring scientific missions of the coming decades.”
The €750 ($920) million Gaia satellite’s journey started in December 2013, and its first data release, which was based on just one year of observations, was published in 2016. This initial survey mapped the distances and motions of two million stars — very impressive, by all means. But, this latest data release, which was collected between 25 July 2014 and 23 May 2016, outshines its predecessor, pinning down the positions of nearly 1.7 billion stars. What’s more, the precision with which some of these stars have been mapped is simply mind-blowing. For instance, some of the brightest stars in the survey have been pinpointed with the same level of precision required for Earthbound observers to be able to spot a Euro coin lying on the surface of the Moon.
“The second Gaia data release represents a huge leap forward with respect to ESA’s Hipparcos satellite, Gaia’s predecessor and the first space mission for astrometry, which surveyed some 118 000 stars almost thirty years ago,” says Anthony Brown of Leiden University, The Netherlands.
Unwinding the Milky Way’s history
Armed with these far more accurate measurements, astronomers can now differentiate between the parallax of stars — the apparent shift in the sky caused by Earth’s yearly orbit around the sun — from their true movements relative to the galactic center. From the most accurate parallax measurements, about ten percent of the total, astronomers can directly estimate distances to individual stars.
All of this is a “big deal” for researchers whose careers are about understanding the Milky Way and its formation, a quest where the accuracy in pinning down the relative movements of its stars is of the utmost importance. Until recently, much of the galaxy’s contents have been obscured by gas and dust, making it difficult to discern its structure from our vantage point. And because the satellite traces how the stars move, scientists can trace their movements back in time, as if winding a clock backward — in the process, which some call galactic archaeology, it’s possible to see how the galaxy evolved over the past 13 billion years.
That’s not all. Gaia also observes objects in our Solar System, like the positions of more than 14,000 known asteroids. An even larger asteroid sample will be compiled in Gaia’s future releases.
Gaia also has locked on to the positions of more than half a million quasars — extremely remote celestial objects, emitting exceptionally large amounts of energy, powered by black holes a billion times as massive as our sun. These objects are used in the survey as beacons that define a reference frame for the celestial coordinates of all other objects in the Gaia catalogue, something that is routinely done in radio waves but now, for the first time, is also available at optical wavelengths.
All in all, scientists expect to make a wealth of new discoveries as a direct result of the new Gaia data release. Already, some astronomers are using the Gaia survey to distinguish between various populations of stars of different ages that are located in different regions of the Milky Way — such as the disc and the halo — and that formed in different ways
“Gaia will greatly advance our understanding of the Universe on all cosmic scales,” says Timo Prusti, Gaia project scientist at ESA.
“Even in the neighbourhood of the Sun, which is the region we thought we understood best, Gaia is revealing new and exciting features.”
These are four giant galaxies located at the center of the cluster Abell 3827, as seen by the Hubble Space Telescope. The distorted image of a more distant galaxy behind the cluster is faintly visible, wrapped around the four galaxies. Credit: NASA/ESA/Richard Massey. Credit: Durham University.
Scientists say there’s five times more dark matter than all known matter but, despite its ubiquity, nobody knows what dark matter really is or how it works. According to a new study, dark matter might be even more elusive than we thought. Speaking at the European Week of Astronomy and Space Science in Liverpool, Dr. Andrew Robertson of Durham University said that his work suggests dark matter doesn’t interact with anything other than gravity.
Left in the dark
Three years ago, Robertson and colleagues were on the verge of a breakthrough in what could have been the first identification of dark matter. Their observations using the Hubble Space Telescope appeared to show that the Abell 3827 cluster, which is about 1.3 billion light-years away from Earth, had separated from the dark matter surrounding it. This could have only happened if dark matter interacted with forces other than gravity — and it would’ve been incredibly important in elucidating the nature of dark matter due to the new clues it could have offered.
“So long as dark matter doesn’t interact with the Universe around it, we are having a hard time working out what it is,” Robertson said in a statement.
However, fresh observations performed by the same group now suggest that dark matter in the Abell 3827 cluster has not separated from its galaxy after all. The conclusion came after the researchers analyzed distorted infrared light from an unrelated background galaxy, which showed the location of the dark matter that had remained unidentified in the previous study. The observations were enabled by the Atacama Large Millimetre Array (ALMA) in Chile, South America.
A view of the four central galaxies at the heart of cluster Abell 3827, at a broader range of wavelengths, including Hubble Space Telescope imaging in the ultraviolet (shown as blue), and Atacama Large Millimetre Array imaging at very long (sub-mm) wavelengths (shown as red contour lines). Credit: NASA/ESA/ESO/Richard Massey.
The researchers say that while the new results indicate that dark matter is staying within its galaxy, this does not necessarily mean that dark matter does not interact with anything. Instead, it could be that the dark matter interacts very little. Alternatively, this particularly galaxy might be moving straight towards us, which implies we would not expect to see its dark matter displaced sideways.
“The search for dark matter is frustrating, but that’s science. When data improves, the conclusions can change,” said Dr. Richard Massey, in the Centre for Extragalactic Astronomy, at Durham University.
Robertson and colleagues will keep looking for the right opportunities and angles in order to probe the nature of dark matter in greater detail than ever. Over the years, the group at Durham has simulated various non-standard dark matter theories using high-powered supercomputers. One interesting theory that the researchers plan to investigate is whether dark matter interactions make clumps of dark matter more spherical. They will have this opportunity once the SuperBIT telescope will be deployed, which gets a clear view by rising above the Earth’s atmosphere under a giant helium balloon.
Scientific reference: “Dark matter dynamics in Abell 3827: new data consistent with standard Cold Dark Matter”, R. Massey et al., Monthly Notices of the Royal Astronomical Society, in press.
Gravitational waves may be forged by the ungodly forces at the center of galaxies, a new study suggests.
Sagittarius A*, the black hole at the centre of our own galaxy. This image was taken with NASA’s Chandra X-Ray Observatory.
Gravitational waves have recently taken the world by storm. After they were first predicted by Einstein a century ago, it took a hundred years and a groundbreaking project which involved an extremely complex experiment setup and over a thousand scientists’ work to prove their existence. Now, researchers are working hard to understand as much as they can about these elusive waves.
Gravitational waves are small ripples in space-time that spread across the universe. The problem with them (and the reason why they’re so hard to detect) is that they’re only formed by extremely powerful interactions, and even then, they have an extremely low amplitude — in fact, their amplitude is so low that Einstein thought we’d never be able to detect them. They were first observed thanks to a pair of black holes which drew closer and closer to each other before ultimately merging. Since then, astronomers have discovered gravitational waves an additional four times. Every episode involved a pair of merging black holes.
Recent data has shown that these events are fairly common, but we still don’t know much about how black hole pairs end up in this scenario in the first place. Furthermore, in order for these events to lead to observable gravitational waves, they need to be in very specific orbits (either very close or very eccentric).
PhD student Joseph Fernandez at Liverpool John Moores University reports that these events might be even more common than we thought, and might be aided by black holes such as the ones found towards the center of our galaxy. Along with his colleagues, Fernandez found that the orbits of these binary black-hole systems can be changed by the black hole that lies in the center of most galaxies, including our own.
Using prediction models, they showed that black hole binaries which wouldn’t merge in the lifetime of the universe can become tight and eccentric under the gravitational influence of other massive black holes, such as the ones at the center of most galaxies. In 10% of all cases, the merger time is reduced by a factor of over 100 — which explains why we have been able to observe several such instances, and also predicts there will be many more occurrences in the future.
The process also flips the binary system orbital plane, making the BHs orbit in the opposite direction to their initial conditions. This could be used as a smoking gun to allow astronomers to identify when the phenomenon is taking place.
The findings haven’t peer-reviewed yet and will be presented at the European Week of Astronomy and Space Science in Liverpool.