- Gravitational waves could help us find out how fast the universe’s expansion is accelerating Yahoo! Voices
- Black hole ripples could help pin down expansion of universe Phys.org
- Black Hole Echoes Could Help Resolve Tension Around How Fast The Universe Is Expanding IFLScience
- Gravitational lensing of waves: A better way to measure the universe’s expansion? Interesting Engineering
- Gravitational Waves Can Be Gravitationally Lensed, and This Could Provide Another Way to Measure the Expansion of the Universe Universe Today
- View Full Coverage on Google News
Tag Archives: Universes
Upgraded LIGO Reactivated: Resumes Unraveling Universe’s Secrets With Enhanced Gravitational Wave Detection – SciTechDaily
- Upgraded LIGO Reactivated: Resumes Unraveling Universe’s Secrets With Enhanced Gravitational Wave Detection SciTechDaily
- A Massive Gravitational Wave Observatory Is Returning to Action Gizmodo
- Gravitational wave lab LIGO roars back online to detect the oldest black hole collisions ever seen Livescience.com
- The LIGO observatory is finally back, now with double the sensitivity Interesting Engineering
- Gravitational-wave detector LIGO is back — and can now spot more colliding black holes than ever Nature.com
- View Full Coverage on Google News
New map of the universe’s matter reveals a possible hole in our understanding of the cosmos
Scientists have made one of the most precise maps of the universe’s matter, and it shows that something may be missing in our best model of the cosmos.
Created by pooling data from two telescopes that observe different types of light, the new map revealed that the universe is less “clumpy” than previous models predicted — a potential sign that the vast cosmic web that connects galaxies is less understood than scientists thought.
According to our current understanding, the cosmic web is a gigantic network of crisscrossing celestial superhighways paved with hydrogen gas and dark matter. Taking shape in the chaotic aftermath of the Big Bang, the web’s tendrils formed as clumps from the roiling broth of the young universe; where multiple strands of the web intersected, galaxies eventually formed. But the new map, published Jan. 31 as three (opens in new tab) separate (opens in new tab) studies (opens in new tab) in the journal Physical Review D, shows that in many parts of the universe, matter is less clumped together and more evenly spread out than theory predicts it should be.
Related: How dark is the cosmic web?
“It seems like there are slightly less fluctuations in the current universe than we would predict assuming our standard cosmological model anchored to the early universe,” co-author Eric Baxter, an astrophysicist at the University of Hawaii, said in a statement (opens in new tab).
Spinning the cosmic web
According to the standard model of cosmology, the universe began taking shape after the Big Bang, when the young cosmos swarmed with particles of both matter and antimatter, which popped into existence only to annihilate each other upon contact. Most of the universe’s building blocks wiped themselves out this way, but the rapidly expanding fabric of space-time, along with some quantum fluctuations, meant that some pockets of the primordial plasma survived here and there.
The force of gravity soon compressed these plasma pockets in on themselves, heating the matter as it was squeezed closer together to such an extent that sound waves traveling at half the speed of light (called baryon acoustic oscillations) rippled outward from the plasma clumps. These ripples pushed away the matter that hadn’t already been drawn into the center of a clump, where it came to rest as a halo around it. At that point, most of the universe’s matter was distributed as a series of thin films surrounding countless cosmic voids, like a nest of soap bubbles in a sink.
Once this matter, primarily hydrogen and helium, had sufficiently cooled, it clotted further to birth the first stars, which, in turn, forged heavier and heavier elements through nuclear fusion.
To map out how the cosmic web was spun, the researchers combined observations taken with the Dark Energy Survey in Chile — which scanned the sky in the near-ultraviolet, visible and near-infrared frequencies from 2013 to 2019 — and the South Pole Telescope, which is located in Antarctica and studies the microwave emissions that make up the cosmic microwave background — the oldest light in the universe.
Though they look at different wavelengths of light, both telescopes use a technique called gravitational lensing to map the clumping of matter. Gravitational lensing occurs when a massive object sits between our telescopes and its source; the more that light coming from a given pocket of space appears warped, the more matter there is in that space. This makes gravitational lensing an excellent tool for tracking both normal matter and its mysterious cousin dark matter, which, despite making up 85% of the universe, doesn’t interact with light except by distorting it with gravity.
With this approach, the researchers used data from both telescopes to pinpoint the location of matter and weed out errors from one telescope’s data set by comparing it to the other’s.
“It functions like a cross-check, so it becomes a much more robust measurement than if you just used one or the other,” co-lead author Chihway Chang (opens in new tab), an astrophysicist at the University of Chicago, said in the statement.
The cosmic matter map the researchers produced closely fitted our understanding of how the universe evolved, except for a key discrepancy: It was more evenly distributed and less clumped than the standard model of cosmology would suggest.
Two possibilities exist to explain this discrepancy. The first is that we’re simply looking at the universe too imprecisely, and that the apparent deviation from the model will disappear as we get better tools to peer at the cosmos with. The second, and more significant, possibility is that our cosmological model is missing some seriously big physics. Finding out which one is true will take more cross-surveys and mappings, as well as a deeper understanding of the cosmological constraints that bind the universe’s soap suds.
“There is no known physical explanation for this discrepancy,” the researchers wrote in one of the studies. “Cross-correlations between surveys … will enable significantly more powerful cross-correlation studies that will deliver some of the most precise and accurate cosmological constraints, and that will allow us to continue stress-testing the [standard cosmological] model.”
Traveling Back in Time Is Possible Inside Universes That Spin : ScienceAlert
It turns out that time travel into the past is actually relatively easy. All you need to do is make the universe rotate.
The famous mathematician Kurt Gödel was a friend and neighbor of Albert Einstein at Princeton. He became incredibly curious about Einstein’s general theory of relativity, which was and continues to be our modern formulation of the gravitational force.
That theory connects the presence of matter and energy to the bending and warping of space and time, and then connects that bending and warping to the behavior of matter and energy.
Gödel was curious as to whether relativity could allow time travel into the past. Einstein’s theory purported to be an ultimate framework for the nature of space and time, and as far as we know time travel into the past is forbidden. So Gödel reckoned that general relativity should automatically disallow it.
And Gödel discovered that actually general relativity is perfectly fine with time travel into the past. The trick is to set the universe in motion.
Gödel constructed a relatively simple and artificial model universe to prove his point. This universe is rotating and contains only one ingredient. That ingredient is a negative cosmological constant that resists the centrifugal force of the rotation to keep the universe static.
Gödel found that if you follow a particular path in this rotating universe you can end up in your own past. You would have to travel incredibly far, billions of light years long, to do it, but it can be done.
As you travel, you would get caught up in the rotation of the universe. That isn’t just a rotation of the stuff in the cosmos, but of both space and time themselves. In essence, the rotation of the universe would so strongly alter your potential paths forward that those paths loop back around to where you started.
You would set off on your journey and never travel faster than the speed of light, and you would find yourself back where you started but in your own past.
The possibility of backwards time travel creates paradoxes and violates our understanding of causality. Thankfully, all observations indicate that the universe is not rotating, so we are protected from Gödel’s problem of backwards time travel.
But it remains to this day a mystery why General Relativity is okay with this seemingly impossible phenomenon. Gödel used the example of the rotating universe to argue that General Relativity is incomplete, and he may yet be right.
This article was originally published by Universe Today. Read the original article.
Astronomers May Have Just Spotted the Universe’s First Galaxies
Scientists just announced that they’ve detected what might be some of the earliest galaxies to form in the universe, a tantalizing discovery made thanks to NASA’s new flagship James Webb Space Telescope.
“This is the first large sample of candidate galaxies beyond the reach of the Hubble Space Telescope,” astronomer Haojing Yan said yesterday at a press conference at the American Astronomical Society meeting in Seattle. Yan, who is at the University of Missouri, led the newly published study. Because the more sensitive JWST can see further into deep space than its predecessor Hubble does, it essentially sees further back in time. In the new catalog of 87 galaxies astronomers have spotted using it, some could date back to about 13.6 billion years ago, just 200 million years after the Big Bang. That’s when the galaxies emitted the light that we’re seeing today—although those systems of stars, gas, and dust would have changed dramatically since then, if they still exist at all.
While scientists have studied other faraway galaxies that date back to when the universe was still young, the discoveries by Yan and his colleagues could break those records by a few hundred million years or so. But at this point, they are all still considered “candidate galaxies,” which means that their birthdates still need confirmation.
Dating a galaxy can be a challenging matter: It involves measuring its “redshift,” how much the light it emits is stretched toward longer red wavelengths, which tells astronomers how fast the galaxy is moving away from us in the quickly expanding universe. That, in turn, tells astronomers the galaxy’s distance from Earth—or more exactly, the distance that the photons from its stars had to travel at the speed of light before reaching a space telescope near the Earth, like JWST. Light from stars in the most distant galaxy in this collection may have been emitted 13.6 billion years ago, likely fairly soon after the young galaxy came together.
These newly estimated distances will have to be confirmed with spectra, which means measuring the light the galaxies emit across the electromagnetic spectrum and pinpointing its unique signatures. Still, Yan expects many of them to be correctly dated to the early days of the cosmos: “I’ll bet $20 and a tall beer that the success rate will be higher than 50 percent,” he said.
Yan’s team imaged these galaxies with JWST’s NIRCam at six near-infrared wavelengths. To estimate their distances, the astronomers used a standard “dropout” technique: Hydrogen gas surrounding galaxies absorbs light at a particular wavelength, so the wavelengths at which an object can or can’t be seen puts a limit on how far away it is likely to be. These 87 candidate galaxies mostly look like blobs that can only be detected in the longer (and therefore redder) near-infrared wavelengths detectable by NIRCam, which could mean they’re very distant, and therefore very old.
However, it’s possible that some of them could be much closer than expected—which would mean they aren’t so old after all. For example, it could be that their light is just too faint to be detected at some wavelengths. Until Yan can collect more detailed data, he won’t know for sure.
We’re on The Brink of Hearing The Universe’s Background Hum. Here’s Why We’re Listening : ScienceAlert
The Universe should be humming.
Every supernova, every merger between neutron stars or black holes, even rapidly spinning lone neutron stars, could or should be a source of gravitational waves.
Event the rapid inflation of space following the Big Bang 13.8 billion years ago should have produced its own cascade of gravitational waves.
Like a rock thrown in a pond, these massive events should send ripples reverberating through the very fabric of space-time – faint expansions and contractions of space that could be detectable to us as discrepancies in what should be precisely timed signals.
Collectively, this mix of signals combines to form a random or ‘stochastic’ buzz known as the gravitational wave background, and it’s one of possibly the most highly-sought detections in gravitational wave astronomy.
The new frontier in space exploration
It’s thought – just as the discovery of the cosmic microwave background did before it (and continues to do) – that finding the gravitational wave background will blow our understanding of the Universe and its evolution wide open.
“Detecting a stochastic background of gravitational radiation can provide a wealth of information about astrophysical source populations and processes in the very early Universe, which are not accessible by any other means,” explains theoretical physicist Susan Scott of the Australian National University and the ARC Centre of Excellence for Gravitational Wave Discovery.
“For example, electromagnetic radiation does not provide a picture of the Universe any earlier than the time of last scattering (about 400,000 years after the Big Bang). Gravitational waves, however, can give us information all the way back to the onset of inflation, just ∼10-32 seconds after the Big Bang.”
To understand the importance of the gravitational wave background, we ought to talk a little bit about another relic of the Big Bang: the cosmic microwave background, or CMB.
Moments after our Universe started ticking and space began to cool, the bubbling foam that was everything congealed into an opaque soup of subatomic particles in the form of ionized plasma.
Any radiation that emerged with it was scattered, preventing it from making it any great distance. It wasn’t until these subatomic particles recombined into atoms, an era known as the Epoch of Recombination, that light could freely move through the Universe and on down through the eons.
The first flash of light burst through space around 380,000 years after the Big Bang, and, as the Universe grew and grew in the following billions of years, this light got dragged into every corner. It’s still all around us today. This radiation is extremely faint but detectable, particularly in microwave wavelengths. This is the CMB, the first light in the Universe.
The irregularities in this light, referred to as anisotropies, were caused by small temperature fluctuations represented by that first light. It’s difficult to overstate how phenomenal its discovery was: the CMB is one of the only probes we have of the state of the early Universe.
The discovery of the gravitational wave background would be a magnificent replication of this achievement.
“We expect the detection and analysis of the gravitational wave background to revolutionize our understanding of the Universe,” Scott says, “in the same way pioneered by the observation of the cosmic microwave background and its anisotropies.”
The buzz beyond the boom-crash
The first detection of gravitational waves was made just a short time ago, in 2015.
Two black holes that collided roughly 1.4 billion years ago sent ripples propagating at light-speed; on Earth, these expansions and contractions of space-time very faintly triggered an instrument designed and refined for decades, waiting to detect just such an event.
It was a monumental detection for several reasons. It gave us direct confirmation, for the first time, of the existence of black holes.
It confirmed a prediction made by the General Theory of Relativity 100 years earlier that gravitational waves are real.
And it meant that this tool, the gravitational wave interferometer, that scientists had been working on for years would revolutionize our understanding of black holes.
And it has. The LIGO and Virgo interferometers have detected nearly 100 gravitational wave events to date: those strong enough to produce a marked signal in the data.
These interferometers use lasers shining down special tunnels several kilometers long. These lasers are affected by the stretching and squeezing of space-time produced by gravitational waves, generating an interference pattern from which scientists can infer the properties of the compact objects generating the signals.
But the gravitational wave background is a different beast.
“An astrophysical background is produced by the confused noise of many weak, independent, and unresolved astrophysical sources,” Scott says.
“Our ground-based gravitational wave detectors LIGO and Virgo have already detected gravitational waves from tens of individual mergers of a pair of black holes, but the astrophysical background from stellar mass binary black hole mergers is expected to be a key source of the GWB for this current generation of detectors. We know that there are a large number of these mergers which cannot be resolved individually, and together they produce a hum of random noise in the detectors.”
The rate at which binary black holes collide in the Universe is unknown, but the rate at which we can detect them gives us a baseline from which we can make an estimate.
Scientists believe it’s between around one merger per minute, and several per hour, with the detectable signal of each lasting just a fraction of a second. These individual, random signals would probably be too faint to detect but would combine to create a staticky background noise; astrophysicists compare it to the sound of popcorn popping.
This would be the source of a stochastic gravitational wave signal we could expect to find with instruments like the LIGO and Virgo interferometers. These instruments are currently undergoing maintenance and preparation and will be joined by a third observatory, KAGRA in Japan, in a new observing run in March 2023. A detection of the popcorn GWB by this collaboration is not out of the question.
These are not the only tools in the gravitational wave kit, though. And other tools will be able to detect other sources of the gravitational wave background. One such tool, still 15 years away, is the Laser Interferometer Space Antenna (LISA), set to be launched in 2037.
It’s based on the same technology as LIGO and Virgo, but with “arms” that are 2.5 million kilometers long. It will operate in a much lower-frequency regime than LIGO and Virgo and will therefore detect different kinds of gravitational wave events.
“The GWB is not always popcorn-like,” Scott tells ScienceAlert.
“It can also consist of individual deterministic signals which overlap in time producing a confusion noise, similar to the background conversations at a party. An example of confusion noise is the gravitational radiation produced by the galactic population of compact white dwarf binaries. This will be an important source of confusion noise for LISA. In this case, the stochastic signal is so strong that it becomes a foreground, acting as an additional source of noise when trying to detect other weak gravitational wave signals in the same frequency band.”
LISA could theoretically also detect cosmological sources of the gravitational wave background, such as cosmic inflation just after the Big Bang or cosmic strings – theoretical cracks in the Universe that could have formed at the end of inflation, losing energy via gravitational waves.
Timing the pulse of the cosmos
There’s also one huge, galactic-scale gravitational wave observatory that scientists have been studying to look for hints of the gravitational wave background: pulsar timing arrays. Pulsars are a type of neutron star, the remains of once-massive stars that have died in a spectacular supernova, leaving just a dense core behind.
Pulsars rotate in such a way that beams of radio emission from their poles sweep past Earth, like a cosmic lighthouse; some of them do so at incredibly precise intervals, which is useful for a range of applications, such as navigation.
But the stretching and squeezing of space-time should, theoretically, produce tiny irregularities in the timing of pulsar flashes.
One pulsar displaying slight inconsistencies in timing might not mean much, but if a bunch of pulsars showed correlated timing inconsistencies, that might be indicative of gravitational waves produced by inspiralling supermassive black holes.
Scientists have found tantalizing hints of this source of the gravitational wave background in pulsar timing arrays, but we don’t yet have enough data to determine if that is the case.
We’re standing so enticingly close to a detection of the gravitational wave background: the astrophysical background, revealing the behavior of black holes throughout the Universe; and the cosmological background – the quantum fluctuations seen in the CMB, inflation, the Big Bang itself.
This, Scott says, is the white whale: the one we’ll only see after the difficult work of teasing apart the background into the discrete sources that make up the noisy whole.
“While we look forward to a wealth of information to come from the detection of an astrophysically produced background, the observation of gravitational waves from the Big Bang is really the ultimate goal of gravitational wave astronomy,” she says.
“By removing this binary black hole foreground, the proposed third generation ground-based detectors, such as the Einstein Telescope and Cosmic Explorer, could be sensitive to a cosmologically produced background with 5 years of observations, thereby entering the realm where important cosmological observations can be made.”
Peekaboo! Strange tiny galaxy provides a glimpse into the universe’s early history
Astronomers have discovered that a strange dwarf galaxy hidden for years in our cosmic neighborhood looks like it belongs in the early universe, despite having formed more recently.
The tiny galaxy measuring just 1,200 light-years across earned the nickname ‘Peekaboo’ because it was hidden in the bright glare of a fast-moving foreground star and only emerged between 50 and 100 years ago.
The dwarf galaxy, bearing the official name HIPASS J1131–31, is located around 22 million light-years from Earth in the constellation of Hydra. Its strange appearance was confirmed using the Hubble Space Telescope after it showed up in observations from other space and ground-based telescopes.
Related: James Webb Space Telescope peers into lonely dwarf galaxy with sparkling results
The galaxy’s faux-ancient appearance comes from the fact that it has low abundances of elements that are heavier than hydrogen and helium, the universe’s lightest and earliest-formed elements. Astronomers describe these heavier elements as ‘metals’ and are usually found in much more distant locations; thus, early galaxies that are typically described as ‘extremely metal-poor.’
As such, HIPASS J1131–31 represents the closest example of a galaxy formed by processes that existed predominantly throughout the universe shortly after the Big Bang.
“Uncovering the Peekaboo Galaxy is like discovering a direct window into the past, allowing us to study its extreme environment and stars at a level of detail that is inaccessible in the distant, early universe,” study co-author and Space Telescope Science Institute astronomer, Gagandeep Anand, said in a statement (opens in new tab).
During the earliest era of the universe, almost everything in the cosmos was composed of hydrogen and helium (opens in new tab). These light elements were formed shortly after the Big Bang when the universe had expanded and cooled enough to allow electrons and protons to bond and form the first atoms and thus the first chemical elements.
These elements formed the first stars, which during their lifetimes forged heavier elements. When this first generation of extremely metal-poor stars reached the end of their lives and exploded, they spread these heavy elements throughout the universe to become the building blocks of the next generation of stars.
As this process repeated throughout cosmic history, each subsequent generation of stars became more and more enriched with heavy elements and created the metal-rich universe that we see throughout our cosmic neighborhood today.
These heavier building blocks forged in earlier stars — particularly carbon, oxygen, iron, and calcium — would also become the foundational elements of life.
Though early and distant galaxies were by default metal-poor, other examples of extremely metal-poor galaxies have previously been discovered closer to the Milky Way, our galaxy.
Peekaboo stands out from these galaxies because it seems to lack an older stellar population of ancient and thus metal-poor stars. Additionally, at just around 20 light-years from Earth, Peekaboo is much closer than other young metal-poor galaxies which are twice as distant.
First discovered two decades ago by research co-author professor Bärbel Koribalski in data collected in the HI Parkes All Sky Survey, the dwarf galaxy HIPASS J1131–31 didn’t immediately present itself as anything special to astronomers. It took observations in far-ultraviolet light by NASA’s now-defunct space-based Galaxy Evolution Explorer (GALEX) mission to reveal Peekaboo’s nature as a strange compact blue dwarf galaxy.
“At first we did not realize how special this little galaxy is,” Koribalski said. “Now with combined data from the Hubble Space Telescope, the Southern African Large Telescope (SALT), and others, we know that the Peekaboo Galaxy is one of the most metal-poor galaxies ever detected.”
Hubble was able to resolve around 60 stars in the dwarf galaxy which all appear to be no older than a few billion years. Astronomers then used SALT to discover Peekaboo’s metal-poor nature, revealing it as one of the youngest and least-chemically-enriched galaxies ever detected in the local universe.
As the local universe has had over 13 billion years to evolve, the metal-poor nature of Peekaboo marks it as extremely unusual and astronomers still have much to learn about this dwarf galaxy.
To improve the snapshot of HIPASS J1131–31 collected by the Hubble observations, which were part of the Every Known Nearby Galaxy Survey, astronomers will now use the James Webb Space Telescope to observe the galaxy alongside Hubble.
Hopefully, this will reveal more about its population of stars and how enriched with metals they are.
“Due to Peekaboo’s proximity to us, we can conduct detailed observations, opening up possibilities of seeing an environment resembling the early universe in unprecedented detail,” Anand concluded.
The team’s research has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.
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An Epic Cosmic Smash-Up May Have Revealed Evidence of The Universe’s Missing Matter : ScienceAlert
A collision between some of the largest structures in space has just given us a clue about one of the biggest mysteries in the Universe: the location of a whole pile of missing matter.
In the galaxy cluster Abell 98 – in which two sub-clusters are in the process of merging – scientists have found a filament of gas consistent with something called the warm-hot intergalactic medium (WHIM).
This fog of plasma thought to float around in between galaxies happens to be one of the leading candidates for the location of a shortfall in the amount of visible, garden-variety particles called ‘baryonic matter’ measured in the local Universe.
Previous evidence suggests that the WHIM is out there, but it’s proven difficult to locate enough of the material to argue how it contributes to the missing baryons.
“Finding these filaments of missing matter has proven to be exceptionally difficult, and only a few examples are known,” says astrophysicist Arnab Sarkar of the Harvard-Smithsonian Center for Astrophysics (CfA). “We are excited that we have likely pinpointed another.”
The missing matter is one of the stranger questions we have about the Universe. We know, more or less, the distribution of matter/energy throughout the cosmos. Most of it is stuff we can’t detect and therefore don’t even know what it is: 68 percent in the form of dark energy and 27 percent as dark matter.
The remaining 5 or so percent is baryonic matter. That’s the stuff that we can detect, and from which everything we see is made: stars, planets, dust, galaxies, clouds, black holes, humans.
We know how much baryonic matter was around at the time of the Big Bang because we have radiation left over from that epoch, the Cosmic Microwave Background (CMB), that scientists have been able to decode.
When scientists started to take stock of the baryonic matter that’s immediately around us today, however, the numbers didn’t add up. There’s a lot missing, between half and a third of what has been predicted based on the CMB.
One possible location for this is the WHIM; filaments of gas with temperatures between 10,000 and 10 million Kelvin, in which baryons are shock-heated and compressed. However, locating these tenuous structures in the space between much brighter galaxies has been tricky.
Enter Abell 98, a cluster of galaxies around 1.4 billion light-years away. X-ray observations of Abell 98 have revealed hot gas structures between two sub-clusters. Earlier this year, Sarkar and his colleagues published an analysis finding that this filament contains a giant shock wave as the sub-clusters come together.
Their analysis also probed the properties of the filament of gas and found two distinct temperature regimes: one at 20 million Kelvin, and the second at 10 million Kelvin. The hotter gas, the researchers say, is likely the result of the gas haloes around the two sub-clusters overlapping.
The cooler gas, on the other hand, is consistent with the hotter, denser end of the theorized WHIM range, the team found.
In a second paper, a team of researchers led by astrophysicist Gabriella Alvarez of CfA has found further evidence for WHIM, not in the space between the two sub-clusters, but on the far side of the sub-cluster, far from the shock front. This, too, was consistent with denser WHIM.
“These measurements,” the researchers write in the paper, “provide tantalizing evidence for the presence of a larger-scale structure, with the diffuse WHIM connecting to the cluster outskirts along cosmic filaments.”
We still haven’t identified enough WHIM to account for all the missing baryons. It could also be hiding in other places; evidence suggests that some may be hiding in gas filaments stretching between galaxies, or lurking as clouds of thin gas in intergalactic space.
But our tools for detecting WHIM are getting more powerful, with new-generation X-ray telescopes taking to the skies. When they peer into the voids between the stars, they should reveal even more of the secrets of deep space, and what lurks therein.
The two papers are to appear, respectively, in The Astrophysical Journal Letters and The Astrophysical Journal, and are available on arXiv. They can be found here and here.
Potential first traces of the universe’s earliest stars – HeritageDaily
Astronomers may have discovered the ancient chemical remains of the first stars to light up the Universe.
Using an innovative analysis of a distant quasar observed by the 8.1-meter Gemini North telescope on Hawai‘i, operated by NSF’s NOIRLab, the scientists found an unusual ratio of elements that, they argue, could only come from the debris produced by the all-consuming explosion of a 300-solar-mass first-generation star.
The very first stars likely formed when the Universe was only 100 million years old, less than one percent its current age. These first stars — known as Population III — were so massive that when they ended their lives as supernovae they tore themselves apart, seeding interstellar space with a distinctive blend of heavy elements. Despite decades of diligent searching by astronomers, however, there has been no direct evidence of these primordial stars, until now.
By analysing one of the most distant known quasars using the Gemini North telescope, one of the two identical telescopes that make up the International Gemini Observatory, operated by NSF’s NOIRLab, astronomers now think they have identified the remnant material of the explosion of a first-generation star. Using an innovative method to deduce the chemical elements contained in the clouds surrounding the quasar, they noticed a highly unusual composition — the material contained over 10 times more iron than magnesium compared to the ratio of these elements found in our Sun.
The scientists believe that the most likely explanation for this striking feature is that the material was left behind by a first-generation star that exploded as a pair-instability supernova. These remarkably powerful versions of supernova explosions have never been witnessed, but are theorized to be the end of life for gigantic stars with masses between 150 and 250 times that of the Sun.
Pair-instability supernova explosions happen when photons in the centre of a star spontaneously turn into electrons and positrons — the positively charged antimatter counterpart to the electron. This conversion reduces the radiation pressure inside the star, allowing gravity to overcome it and leading to the collapse and subsequent explosion.
Unlike other supernovae, these dramatic events leave no stellar remnants, such as a neutron star or a black hole, and instead eject all their material into their surroundings. There are only two ways to find evidence of them. The first is to catch a pair-instability supernova as it happens, which is a highly unlikely happenstance. The other way is to identify their chemical signature from the material they eject into interstellar space.
For their research, the astronomers studied results from a prior observation taken by the 8.1-meter Gemini North telescope using the Gemini Near-Infrared Spectrograph (GNIRS). A spectrograph splits the light emitted by celestial objects into its constituent wavelengths, which carry information about which elements the objects contain. Gemini is one of the few telescopes of its size with suitable equipment to perform such observations.
Deducing the quantities of each element present, however, is a tricky endeavour because the brightness of a line in a spectrum depends on many other factors besides the element’s abundance.
Two co-authors of the analysis, Yuzuru Yoshii and Hiroaki Sameshima of the University of Tokyo, have tackled this problem by developing a method of using the intensity of wavelengths in a quasar spectrum to estimate the abundance of the elements present there. It was by using this method to analyze the quasar’s spectrum that they and their colleagues discovered the conspicuously low magnesium-to-iron ratio.
“It was obvious to me that the supernova candidate for this would be a pair-instability supernova of a Population III star, in which the entire star explodes without leaving any remnant behind,” said Yoshii. “I was delighted and somewhat surprised to find that a pair-instability supernova of a star with a mass about 300 times that of the Sun provides a ratio of magnesium to iron that agrees with the low value we derived for the quasar.”
Searches for chemical evidence for a previous generation of high-mass Population III stars have been carried out before among the stars in the halo of the Milky Way and at least one tentative identification was presented in 2014. Yoshii and his colleagues, however, think the new result provides the clearest signature of a pair-instability supernova based on the extremely low magnesium-to-iron abundance ratio presented in this quasar.
If this is indeed evidence of one of the first stars and of the remains of a pair-instability supernova, this discovery will help to fill in our picture of how the matter in the Universe came to evolve into what it is today, including us. To test this interpretation more thoroughly, many more observations are required to see if other objects have similar characteristics.
But we may be able to find the chemical signatures closer to home, too. Although high-mass Population III stars would all have died out long ago, the chemical fingerprints they leave behind in their ejected material can last much longer and may still linger on today. This means that astronomers might be able to find the signatures of pair-instability supernova explosions of long-gone stars still imprinted on objects in our local Universe.
“We now know what to look for; we have a pathway,” said co-author Timothy Beers, an astronomer at the University of Notre Dame. “If this happened locally in the very early Universe, which it should have done, then we would expect to find evidence for it.”
Association of Universities for Research in Astronomy (AURA)
https://doi.org/10.48550/arXiv.2207.11909
Image Credit : NOIRLab/NSF/AURA/J. da Silva/Spaceengine
JWST spots ‘Sparkler Galaxy’ that could host universe’s 1st stars
The first science-quality image revealed from NASA’s newest space telescope contained a hidden treasure in the form of a sparking distant galaxy surrounded by dense clusters that could contain some of the universe’s first stars.
That image, the first deep-field image from the James Webb Space Telescope (JWST), offered a stunning array of galaxies. And a team of Canadian astronomers have zoomed in on a galaxy located 9 billion light-years away from Earth, dubbed the “Sparkler Galaxy” because the compact objects surrounding it appear as small sparkling yellow-red dots. The galaxy is remarkable in itself for its weird stretched appearance, but the surrounding objects that inspired the nickname are of particular scientific interest, since they could be the most distant globular clusters of stars ever found by astronomers.
Globular clusters are collections of ancient stars that date back to a galaxy’s infancy, so they can contain clues about the early stages of galactic formation, growth and evolution. Looking at the 12 compact objects surrounding the Sparkler Galaxy, the Canadian NIRISS Unbiased Cluster Survey (CANUCS) team that found five of them are indeed globular clusters. Moreover, these could be some of the oldest globular clusters ever seen, perhaps dating back to the time when the universe first began to birth stars.
“It was really surprising to us that that we were able to find such a unique object so early on in the JWST data,” Kartheik G. Iyer, an astronomer at the University of Toronto in Canada and co-lead author of the study, told Space.com. “According to our analysis, we found that most of these sparkles around the main body of the galaxy are really massive and really old, stellar systems.”
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The JWST image allowed the team to observe the ‘sparkles’ across a range of wavelengths, Iyer noted, meaning the scientists could model the clusters precisely to better understand their physical properties, including their age and the number of stars they contain. Using such distant globular clusters to date the first stars in faraway early galaxies wasn’t possible before JWST.
“What we’re trying to do is we’re trying to age-date all the objects in the universe — the stars, the galaxies and the globular clusters — because we want to know, when is it that stars started to be born?” Lamiya Mowla, the study’s co-author and also an astronomer at the University of Toronto, told Space.com.
The Milky Way contains an estimated 150 globular clusters, but scientists have struggled to determine their ages. Mowla explained that while it is relatively easy to age-date most things in our galaxy, this isn’t the case with particularly ancient objects, which already appear old when viewed up-close and thus more recently in time. It’s much easier to date more distant clusters like the Sparkler Galaxy, which astronomers see as they were 9 billion years ago, when the cluster was much younger and the universe itself just 4.5 billion years old.
Think of globular clusters aging like humans do, Mowla said. “Aging globular clusters in the Milky Way is like looking at a picture trying to say if a person is 50 years old or if this person is a 55-year-old,” she said. “It’s easier to tell if somebody is 5 years old or if they’re 10 years old. It’s even easier to tell if they are a 1-year-old or if they’re a 6-year-old.”
And because astronomers are seeing the globular clusters surrounding the Sparkler Galaxy as they were 9 billion years ago, they look very young, making determining their age like looking at the image of the infant rather than the middle-aged person.
The astronomers further confirmed the age of the clusters using data from the Canadian-made Near-Infrared Imager and Slitless Spectrograph (NIRISS) instrument on the JWST. NIRISS observations revealed no sign of oxygen, which is usually associated with young clusters that are actively forming stars.
The JWST got an assist in the observation of the Sparkler Galaxy from both the Hubble Space Telescope, which has observed the galaxy before but was unable to resolve the globular clusters surrounding it, and from a natural phenomenon called gravitational lensing.
A helping hand from general relativity
Gravitational lensing was first predicted in 1915 by Einstein’s theory of general relativity and has since become a powerful tool for astronomers.
General relativity says that objects of great mass curve the fabric of spacetime. Think of this as akin to placing balls of increasing mass on a stretched rubber sheet: the larger the mass, the greater the “dent,” or curvature, it causes. In space, this curvature bends the path of light. When the mass of a foreground lensing object is extreme, this can make a background object — the source of this light — appear much larger or in multiple places in an image.
Gravitational lensing is what gives the Sparkler Galaxy its weird, stretched shape and magnifies it enough for JWST to spot it. The phenomenon also makes several of the surrounding clusters appear at multiple points in the JWST deep-field image.
Together, the magnification and the multiple images created by gravitational lensing both helped with the study of these objects but also helped confirm that these clusters do indeed orbit the Sparkler Galaxy and aren’t just “overlaid” on top of it in JWST’s line of view.
One of the remaining questions surrounding the Sparkler Galaxy is just how much the foreground lensing object, the SMACS 0723 galaxy cluster, is magnifying it.
“The magnification of the Sparkler Galaxy and its surroundings is not as well constrained as we’d like,” Iyer said. “So one of the things we want to do is build a better magnification model so that we can figure out whether it’s enlarged by a factor of 10 or by a factor of 100.”
Figuring out by how much the Sparkler Galaxy and its clusters are magnified could help determine properties such as their age and their distance from Earth more precisely.
The CANUCS team will also be using JWST telescope in October to study five massive clusters of galaxies, around which they expect to find more systems like those around the Sparkler Galaxy.
“We hope the knowledge that globular clusters can be observed at from such great distances with the JWST will spur further science and searches for similar objects,” Iyer said.
The James Webb Space Telescope’s impact on astronomy
Astronomers and space fans alike had eagerly awaited the release of JWST’s first images. Iyer said that some of his CANUCS colleagues didn’t sleep on the night that the deep-field image was revealed, and Mowla looked back on the excitement of the night and how quickly the search for important cosmic objects began.
“The big reveal came from NASA in the evening and the next day the whole CANUCS collaboration were together looking at this image together,” Mowla said.
“Then we saw this weirdly shaped highly lensed system,” she added. “Even in the color image this thing pops out and there are these star clusters, like these little dots, that you don’t see in other galaxies.”
The discovery of such distant globular clusters in the first deep-field image from JWST is an example of how the telescope is continuing to deliver impressive findings and, in the process, shaping astronomy’s future, they said. The duo are referring to the fact that while the Sparkler Galaxy and its globular companions are distant enough to be seen when the universe was only about 4 billion years old, this is still comparatively close considering that the JWST was designed to see galaxies as they were just hundreds of millions of years after the Big Bang.
“We are getting data that is deeper than we anticipated, which is quite surprising in the most beautiful way,” Mowla said.
And for Mowla, an early-career researcher, the timing couldn’t be better. “It’s an incredible time for us as young astronomers who are just starting out,” she added. “People have been waiting for this telescope for so long, so we feel incredibly lucky to have this telescope right at the beginning of our careers.”
The team’s research was published on Thursday (Sept. 29) in the Astrophysical Journal Letters.
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