Astronomers Create 8 Million Baby Universes Inside A Computer

(THIS ARTICLE IS COURTESY OF LIVE SCIENCE)

 

Astronomers Create 8 Million Baby Universes Inside a Computer and Watch Them Grow. Here’s What They Learned.

helix nebula

(Image: © Shutterstock)

A team of astrophysicists has just spawned 8 million unique universes inside a supercomputer and let them evolve from just tots to old geezers. Their goal? To nail down the role that an invisible substance called dark matter played in our universe’s life since the Big Bang and what it means for our fate.

After discovering that our universe is mostly composed of dark matter in the late 1960s, scientists have speculated on its role in the formation of galaxies and their ability to give birth to new stars over time.

According to the Big Bang theory, not long after the universe was born, an invisible and elusive substance physicists have dubbed dark matter began to clump together by the force of gravity into massive clouds called dark matter haloes. As the haloes grew in size, they attracted the sparse hydrogen gas permeating the universe to come together and form the stars and galaxies we see today. In this theory, dark matter acts as the backbone of galaxies, dictating how they form, merge and evolve over time.

Related: The 11 Biggest Unanswered Questions About Dark Matter

To better understand how dark matter shaped this history of the universe, Peter Behroozi, an assistant professor of astronomy at the University of Arizona, and his team created his own universes using the school’s supercomputer. The computer’s 2,000 processors worked without pause over a span of three weeks to simulate more than 8 million unique universes. Each universe individually obeyed a unique set of rules to help researchers understand the relationship between dark matter and the evolution of galaxies.

“On the computer, we can create many different universes and compare them to the actual one, and that lets us infer which rules lead to the one we see,” Behroozi said in a statement.

While previous simulations have focused on modeling single galaxies or generating mock universes with limited parameters, the UniverseMachine is the first of its scope. The program continuously created millions of universes, each containing 12 million galaxies, and each allowed to evolve over nearly the entire history of the real universe from 400 million years after the Big Bang to the present day.

“The big question is, ‘How do galaxies form?’” said study researcher Risa Wechsler, a professor of physics and astrophysics at Stanford University. “The really cool thing about this study is that we can use all the data we have about galaxy evolution —  the numbers of galaxies, how many stars they have and how they form those stars — and put that together into a comprehensive picture of the last 13 billion years of the universe.”

Related: From the Big Bang to Present: Snapshots of Our Universe Through Time

Creating a replica of our universe, or even of a galaxy, would require an inexplicable amount of computing power. So Behroozi and his colleagues narrowed their focus to two key properties of galaxies: their combined mass of stars and the rate at which they give birth to new ones.

“Simulating a single galaxy requires 10 to the 48th computing operations,” Behroozi explained, referring to an octillion operation, or a 1 followed by 48 zeros. “All computers on Earth combined could not do this in a hundred years. So to just simulate a single galaxy, let alone 12 million, we had to do this differently.”

As the computer program spawns new universes, it makes a guess on how a galaxy’s rate of star formation is related to its age, its past interactions with other galaxies and the amount of dark matter in its halo. It then compares each universe with real observations, fine-tuning the physical parameters with every iteration to better match reality. The end result is a universe nearly identical to our own.

According to Wechsler, their results showed that the rate at which galaxies give birth to stars is tightly connected to the mass of their dark matter haloes. Galaxies with dark matter halo masses most similar to our own Milky Way had the highest star-formation rates. She explained that star formation is stifled in more massive galaxies by an abundance of blackholes

Their observations also challenged long-held beliefs that dark matter stifled star formation in the early universe.

“As we go back earlier and earlier in the universe, we would expect the dark matter to be denser, and therefore the gas to be getting hotter and hotter. This is bad for star formation, so we had thought that many galaxies in the early universe should have stopped forming stars a long time ago,” Behroozi said. “But we found the opposite: Galaxies of a given size were more likely to form stars at a higher rate, contrary to the expectation.”

Now, the team plans to expand the Universe Machine to test more ways dark matter might affect the properties of galaxies, including how their shapes evolve, the mass of their black holes and how often their stars go supernova.

“For me, the most exciting thing is that we now have a model where we can start to ask all of these questions in a framework that works,” Wechsler said. “We have a model that is inexpensive enough computationally, that we can essentially calculate an entire universe in about a second. Then we can afford to do that millions of times and explore all of the parameter space.”

The research group published their results in the September issue of the journal Monthly Notices of the Royal Astronomical Society.

Originally published on Live Science.

What Is the Universe Made of?

(THIS ARTICLE IS COURTESY OF LIVE SCIENCE)

 

What Is the Universe Made of?

Image of galaxy cluster Abell 2744 shows dark matter locations

In this image of galaxy cluster Abell 2744, a blue overlay shows the location of dark matter, which makes up about 75% of the cluster’s mass.
(Image: © NASA/ESA/ESO/CXC, and D. Coe (STScI)/J. Merten (Heidelberg/Bologna))

The universe is filled with billions of galaxies and trillions of stars, along with nearly uncountable numbers of planets, moons, asteroids, comets and clouds of dust and gas – all swirling in the vastness of space.

But if we zoom in, what are the building blocks of these celestial bodies, and where did they come from?

Hydrogen is the most common element found in the universe, followed by helium; together, they make up nearly all ordinary matter. But this accounts for only a tiny slice of the universe — about 5%. All the rest is made of stuff that can’t be seen and can only be detected indirectly. [From Big Bang to Present: Snapshots of Our Universe Through Time]

Mostly hydrogen

It all started with a Big Bang, about 13.8 billion years ago, when ultra-hot and densely packed matter suddenly and rapidly expanded in all directions at once. Milliseconds later, the newborn universe was a heaving mass of neutrons, protons, electrons, photons and other subatomic particles, roiling at about 100 billion degrees Kelvin, according to NASA.

Every bit of matter that makes up all the known elements in the periodic table — and every object in the universe, from black holes to massive stars to specks of space dust — was created during the Big Bang, said Neta Bahcall, a professor of astronomy in the Department of Astrophysical Sciences at Princeton University in New Jersey.

“We don’t even know the laws of physics that would have existed in such a hot, dense environment,” Bahcall told Live Science.

About 100 seconds after the Big Bang, the temperature dropped to a still-seething 1 billion degrees Kelvin. By roughly 380,000 years later, the universe had cooled enough for protons and neutrons to come together and form lithium, helium and the hydrogen isotope deuterium, while free electrons were trapped to form neutral atoms.

Because there were so many protons zipping around in the early universe, hydrogen — the lightest element, with just one proton and one neutron — became the most abundant element, making up nearly 95% percent of the universe’s atoms. Close to 5% of the universe’s atoms are helium, according to NASA. Then, about 200 million years after the Big Bang, the first stars formed and produced the rest of the elements, which make up a fraction of the remaining 1% of all ordinary matter in the universe.

Unseen particles

Something else was created during the Big Bang: dark matter. “But we can’t say what form it took, because we haven’t detected those particles,” Bahcall told Live Science.

Dark matter can’t be observed directly — yet — but its fingerprints are preserved in the universe’s first light, or the cosmic microwave background radiation (CMB), as tiny fluctuations in radiation, Bahcall said. Scientists first proposed the existence of dark matter in the 1930’s, theorizing that dark matter’s unseen pull must be what held together fast-moving galaxy clusters. Decades later, in the 1970’s, American astronomer Vera Rubin found more indirect evidence of dark matter in the faster-than-expected rotation rates of stars.

Based on Rubin’s findings, astrophysicists calculated that dark matter — even though it couldn’t be seen or measured — must make up a significant portion of the universe. But about 20 years ago, scientists discovered that the universe held something even stranger than dark matter; dark energy, which is thought to be significantly more abundant than either matter or dark matter. [Gallery: Dark Matter Throughout the Universe]

Hubble Space Telescope Image

Captured in 2014 by the Hubble Space Telescope, this picture of the evolving universe is among Hubble’s most colorful deep-space images.

(Image credit: NASA/ESA)

An irresistible force

The discovery of dark energy came about because scientists wondered if there was enough dark matter in the universe to cause expansion to sputter out or reverse direction, causing the universe to collapse inward on itself.

Lo and behold, when a team of researchers investigated this in the late 1990s, they found that not only was the universe not collapsing in on itself, it was expanding outward at an ever faster rate. The group determined that an unknown force — dubbed dark energy — was pushing against the universe in the apparent void of space and accelerating its momentum; the scientists’ findings earned physicists Adam Riess, Brian Schmidt and Saul Perlmutter the Nobel Prize in Physics in 2011.

Models of the force required to explain the universe’s accelerating expansion rate suggest that dark energy must make up between 70% and 75% of the universe. Dark matter, meanwhile, accounts for about 20% to 25%, while so-called ordinary matter — the stuff we can actually see — is estimated to make up less than 5% of the universe, Bahcall said.

Considering that dark energy makes up about three-quarters of the universe, understanding it is arguably the biggest challenge facing scientists today, astrophysicist Mario Livio, then with the Space Telescope Science Institute at Johns Hopkins University in Baltimore, Maryland, told Live Science sister site Space.com in 2018.

“While dark energy has not played a huge role in the evolution of the universe in the past, it will play the dominant role in the evolution in the future,” Livio said. “The fate of the universe depends on the nature of dark energy.”

Originally published on Live Science.

“One Trillion Times Age Of The Cosmos”–Rarest Thing Ever Detected

(THIS ARTICLE IS COURTESY OF THE ‘DAILY GALAXY’)

 

“One Trillion Times Age of the Cosmos” –Rarest Thing Ever Detected

 

Cluster Abell 3827

 

“We actually saw this decay happen. It’s the longest, slowest process that has ever been directly observed, and our dark matter detector was sensitive enough to measure it,” said Ethan Brown, an assistant professor of physics at Rensselaer Polytechnic Institute. “It’s an amazing to have witnessed this process, and it says that our detector can measure the rarest thing ever recorded.”

How do you observe a process that takes more than one trillion times longer than the age of the universe? The XENON Collaboration research team did it with an instrument built to find the most elusive particle in the universe—dark matter. In a paper to be published tomorrow in the journal Nature, researchers announce that they have observed the radioactive decay of xenon-124, which has a half-life of 1.8 X 1022 years.

The XENON Collaboration runs XENON1T, a 1,300-kilogram vat of super-pure liquid xenon shielded from cosmic rays in a cryostat submerged in water deep 1,500 meters beneath the Gran Sasso mountains of Italy. The researchers search for dark matter by recording tiny flashes of light created when particles interact with xenon inside the detector. And while XENON1T was built to capture the interaction between a dark matter particle and the nucleus of a xenon atom, the detector actually picks up signals from any interactions with the xenon.

Dark Matter –“Emerged From an Eon Before the Big Bang” (Weekend Feature)

The evidence for xenon decay was produced as a proton inside the nucleus of a xenon atom converted into a neutron. In most elements subject to decay, that happens when one electron is pulled into the nucleus. But a proton in a xenon atom must absorb two electrons to convert into a neutron, an event called “double-electron capture.”

Double-electron capture only happens when two of the electrons are right next to the nucleus at just the right time, Brown said, which is “a rare thing multiplied by another rare thing, making it ultra-rare.”

When the ultra-rare happened, and a double-electron capture occurred inside the detector, instruments picked up the signal of electrons in the atom re-arranging to fill in for the two that were absorbed into the nucleus.

“Ultralight” –‘Dark Matter Exists Beyond the Standard Model’

“Electrons in double-capture are removed from the innermost shell around the nucleus, and that creates room in that shell,” said Brown. “The remaining electrons collapse to the ground state, and we saw this collapse process in our detector.”

The achievement is the first time scientists have measured the half-life of this xenon isotope based on a direct observation of its radioactive decay.

“This is a fascinating finding that advances the frontiers of knowledge about the most fundamental characteristics of matter,” said Curt Breneman, dean of the School of Science. “Dr. Brown’s work in calibrating the detector and ensuring that the xenon is scrubbed to the highest possible standard of purity was critical to making this important observation.”

Very Weird Galaxies –“The Absence of Dark Matter is Unprecedented”

The XENON Collaboration includes more than 160 scientists from Europe, the United States, and the Middle East, and, since 2002, has operated three successively more sensitive liquid xenon detectors in the Gran Sasso National Laboratory in Italy. XENON1T, the largest detector of its type ever built, acquired data from 2016 until December 2018, when it was switched off. Scientists are currently upgrading the experiment for the new XENONnT phase, which will feature an active detector mass three times larger than XENON1T. Together with a reduced background level, this will boost the detector’s sensitivity by an order of magnitude.

Three years ago researchers were excited to find that a galaxy at the heart of cluster Abell 3827 shown at the top of the page that appeared to have separated from the dark matter that surrounded it. New research suggests this is incorrect. (Nasa/ESA/Richard Massey)

The Daily Galaxy via Rensselaer Polytechnic Institute

Dark Matter And Black Holes

(THIS ARTICLE IS COURTESY OF ‘WIRED’ NEWS)

 

WHEN IT COMES to the nature of dark matter, astronomers are still largely, well, in the dark. The existence of this mysterious substance was hypothesized more than 40 years ago to explain discrepancies between the calculations of how galaxies ought to behave, based on their mass, and what was actually observed. In short, it seemed like mass was missing. So Vera Rubin, the astronomer who first discovered this discrepancy, conjured an invisible substance that is far more abundant than “normal” matter and acts as the scaffolding for the large-scale structure of the universe. Today we call it dark matter.

Yet decades of hunting for the elusive dark matter particle still have not yielded direct evidence of its existence. Most cosmologists still believe that dark matter must exist, but some have splintered off to propose other explanations that explain away dark matter by modifying our understanding of gravity.

But two findings are now casting doubt on the modified gravity explanation. In March, a team of astronomers led by Yale professor Pieter van Dokkum and his graduate student Shany Danieli published two papers, one confirming the existence of a galaxy that appears to have almost no dark matter and the other announcing the discovery of a second galaxy of this type. The irony, the researchers say, is that the seeming lack of dark matter in these galaxies is strong evidence that it exists.

The reason they believe these galaxies have no dark matter is that their dynamics can be predicted using our traditional theories of gravity. The discrepancy of the “missing mass” that’s seen in most galaxies isn’t present here, meaning there’s no need for dark matter to explain their behavior. And it means that the modified version of gravity proposed by some cosmologists doesn’t predict these galaxies’ movements as cleanly as good old Newtonian physics.

The discovery of these dark-matter-free galaxies traces back to 2014, when van Dokkum and his colleagues finished building Dragonfly, a new kind of telescope, made of off-the-shelf telephoto camera lenses, that specializes in observing extremely faint celestial objects. Only a year after its first light, Dragonfly discovered a new galaxy characterized by an extreme lack of stars relative to its size. Known as an ultra-diffuse galaxy, this ghostly celestial object had roughly the same mass as our Milky Way, but only one hundredth of one percent of that mass could be attributed to “normal” matter like stars. In other words, van Dokkum and his colleagues had discovered a galaxy made of 99.99 percent dark matter.

While this galaxy was unique, its existence isn’t entirely surprising. Most cosmologists think that dense collections of dark matter act as a sort of seed for the formation of large celestial objects like galaxies. The general idea, says Anže Slosar, an astrophysicist at Brookhaven National Laboratory, is that once a collection of dark matter reaches a critical density, it collapses under its own gravity and forms a so-called “dark matter halo.” This halo, in turn, gravitationally attracts hydrogen gas to its center, where it begins to form stars and, eventually, galaxies. The mass of a dark matter halo varies from galaxy to galaxy, but it seemed like every galaxy must have at least some dark matter to keep its form. Indeed, this assumption was precisely what made Dragonfly’s next discovery so surprising.

In 2016, van Dokkum and his colleagues at Yale discovered NGC 1052-DF2, an ultra-diffuse galaxy that appeared to contain little to no dark matter at all. Last year, when the Yale astronomers published their results in the journal Nature, their peers in the cosmological community were incredulous. This was the first galaxy ever discovered that appeared to lack any dark matter, and as Carl Sagan rightly observed, “extraordinary claims require extraordinary evidence”—which is what many cosmologists thought the Yale team was missing.

University of Pennsylvania astrophysicist Robyn Sanderson says the skepticism about DF2 sprang mostly from the limited amount of data used to draw the conclusion. In this case, the Yale team was using data from just 10 star clusters observed over a period of two nights. This meant it was possible they were overlooking key details of the star clusters’ motion, which would distort their estimations of the galaxy’s mass—and undermine their claim that it lacked dark matter.

The Yale researchers recognized this possible source of error themselves when they published their paper on DF2. The only way to resolve this conundrum was to make more detailed measurements or to find another galaxy with characteristics similar to DF2. In March, the Yale team published two papers that did exactly these things.

The first paper offered more refined measurements of stellar velocities within DF2. This time, rather than just measuring the velocities of 10 star clusters, van Dokkum and Danieli used the Keck telescope in Hawaii to observe the velocities of the stars within the star clusters. This approach produced far more data that reinforced the team’s earlier conclusion that the galaxy lacked dark matter.

The other paper announced the discovery of a second galaxy, DF4, which also appears to have little, if any, dark matter. Not only does this increase the odds that the DF2 observations are accurate, it also means such ultra-diffuse galaxies might not be so rare. The fact that two were found in quick succession, Danieli says, was “really reassuring.” Nevertheless, she says “it’s still too early to say whether they are super rare or quite common.” The team will begin observing other nearby ultra-diffuse galaxies next month in an effort to answer this question.

But that won’t resolve the mystery of how these strange galaxies came to exist in the first place. Theoretical cosmologists will have to run simulations to determine how a galaxy can lose its dark matter, she says. One leading theory involves tidal interactions, which is astronomer-speak for when the gravitational forces of two neighboring galaxies pull material from each galaxy and distort them. DF2 and DF4 are both near the galaxy NGC 1052, which makes it a strong candidate for the galaxy that stole their dark matter.

However they came to be, Danieli argues that the existence of these galaxies is a blow to the modified gravityexplanation for why most galaxies don’t behave as we’d expect.

Known as modified Newtonian dynamics, or MOND, this theory recasts gravity such that it has different effects at the galactic scale. Although MOND has successfully predicted the stellar dynamics of hundreds of galaxies, most of which are relatively isolated, it must be able to predict the dynamics of all galaxies to dethrone dark matter as the going cosmological theory.

As Slosar explains it, the discovery of DF2 and DF4 strengthens the case for the existence of a dark matter particle because it means that it can be separated from normal matter. Because these galaxies behave in line with standard gravitational theory, using the equations discovered by Newton and Kepler, they present a challenge to MOND.

“If you find galaxies, some of which have a lot of dark matter and some of which have a little dark matter, you can’t explain it with the loss of gravity unless you’re willing to say that one part of the universe has a different law of gravity than another part, which is just silly,” Slosar says. “The entire point of physics is to find unified laws that are always there. This is why it is an argument for the existence of dark matter.”

So does the existence of galaxies devoid of dark matter pose an existential threat for MOND? Stacy McGaugh, an astronomer at Case Western Reserve University, doesn’t think so. “When DF2 was first discovered, it was portrayed as a huge problem for MOND,” McGaugh says. “On more careful analysis, it turned out that the prediction of MOND was spot-on what was observed.”

The analysis by McGaugh and his colleagues of DF2’s implications for MOND hinges on the galaxy’s proximity to the massive elliptical galaxy NGC1052. Under a set of “reasonable” assumptions, paired with equations from MOND, McGaugh and his colleagues found that NGC1052’s gravitational effects on DF2 would return stellar velocities similar to what van Dokkum and Danieli actually observed. Although he hasn’t had the chance to repeat this analysis for DF4, McGaugh says it also “appears to be consistent with MOND, since it is likely affected by NGC 1052.”

The existence of these galaxies poses a number of vexing problems for the theory of galactic formation, which must account for how a galaxy can come to be violently stripped of its dark matter and still retain the relative order seen, for example, in the presence of star clusters in DF2 and DF4. Will further observations of ultra-diffuse galaxies resolve the dark matter debate? Probably not, but they will, at least, shed some light on the matter.


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