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Category: cosmology – Page 2

Dark Stars May Have Left a Gravitational-Wave Signal We Can Detect Today

A new study suggests that pulsar timing arrays could help reveal how the Universe’s first supermassive black holes formed.

A faint background of extremely low-frequency gravitational waves, detected by monitoring networks of pulsars, may preserve clues from events that began more than 13 billion years ago. Among them could be the processes that produced some of the Universe’s earliest supermassive black holes.

Sohan Ghodla and Cosmin Ilie of Colgate University explored that possibility in a study published as a Letter in Physical Review D. Their goal was to determine whether supermassive black holes that originated in the early Universe could eventually account for a substantial share of the gravitational wave background now detected by Pulsar Timing Arrays, or PTAs.

Going beyond simple models of neural networks: Extended mean-field theory offers a better approach

Physics is most readily applied to relatively simple systems: a pendulum, two electrons colliding or the structure of the solar system. But when systems become complicated—when many particles interact with one another, in condensed matter systems such as gases and fluids or in the cosmology of the early universe—simplifications can be made using a technique called classical or extended mean-field theory.

A research group from Princeton University, led by lead author Luca Di Carlo, has applied extended mean-field theory to networks of biological neurons. Their work is published in the journal Physical Review Letters. They found that the simplest versions of mean-field theory failed to accurately describe the activity of these networks, but an enhanced version was able to do so.

JWST spots a bizarre “black hole star” 100 billion times brighter than a star

Astronomers may have uncovered an entirely new cosmic object: a gigantic “black hole star” that could explain the mysterious red dots filling the early universe. Astronomers from MIT and other institutions have identified an exceptionally bright red object dating back to the early universe. At first glance, it resembles an enormous star with dimensions comparable to our solar system. Its energy output, however, is extraordinary. The object is producing roughly 100 billion times more energy than any known star could physically generate, putting its power much closer to the levels associated with black holes.

That unusual combination has led researchers to propose that the red object represents an entirely new kind of astrophysical source. They are calling it a “black hole star.”

A study published on August 12 in Nature describes the object and the team’s analysis of observations made with NASA’s James Webb Space Telescope (JWST). The telescope detected the bright red dot in the very early universe, only a few hundred million years after the Big Bang.

Gamma-ray signal could be long awaited evidence for WIMPs

Dark matter is known to make up roughly 85% of all mass in the universe, as evidenced by the way galaxies spin and how galaxy clusters are held together under gravity. Yet despite decades of searching, physicists have never managed to detect the elusive substance directly.

In new research published in Physical Review Letters, a team led by Yi-Zhong Fan at the Chinese Academy of Sciences claims to have spotted a strong gamma-ray signal coming from a group of galaxy clusters, which could be among the most compelling evidence yet for a leading dark matter candidate known as WIMPs.

Lunar Regolith Unlocks 100-Million-Year Supernova History

Researchers have developed a model that accounts for chaotic lunar impact gardening, enabling scientists to use lunar regolith to trace supernova history back over 100 million years.

What can lunar regolith (often mistakenly called “soil”) teach scientists about the universe’s history? This is what a recent study published in Physical Review Letters hopes to address as a team of scientists investigated how lunar regolith could be used to study supernova explosions. This study has the potential to help scientists develop new methods for studying the cosmos aside from telescopic observations and data.

For the study, the researchers addressed a longstanding conundrum in lunar science called “impact gardening”, which involves the natural mixing of the lunar regolith during impact strikes, even micrometeorites. As a result, using the lunar regolith to study phenomena like the solar or cosmic radiation becomes scrambles since this mixture contains “information” from a variety of time periods. However, the researchers introduced a new model using Apollo lunar regolith samples by reducing the gardening “noise” within the sample.

In the end, the researchers successfully identified the depth of Iron-60, Plutonium-244, Iodine-129, Hafnium-182, and Curium-247, which are known fingerprints of supernova explosions. The team compared this new model with known supernova impacts on Earth and used that data to create a forward-looking model to ascertain how the lunar regolith would store this information.

Active supermassive black holes may help form massive planets

A popular myth about black holes is that they act like giant cosmic vacuum cleaners, sucking in everything around them. But Wladimir Lyra’s research found a new mechanism around supermassive black holes that is more like a cosmic nursery, giving birth to planets more massive than Jupiter.

“We’re finding objects that are a thousand times the mass of the Earth, but built of pure dust,” Lyra said. “And not only that, but also some of these objects are approaching the mass of the sun.”

Lyra, an associate professor of astronomy at New Mexico State University, began this line of research as a postdoctoral fellow collaborating with Barry McKernan, Saavik Ford and Mordecai-Mark Mac Low at the American Museum of Natural History in 2010.

JWST Finds a “Star” 100 Billion Times Brighter Than Any Star Should Be

Something in the young universe is shining like a star that should not be possible.

NASA’s James Webb Space Telescope has detected a compact red object so luminous that ordinary nuclear fusion cannot plausibly explain it. Although the source has a star-like appearance and may be surrounded by gas on the scale of the solar system, it radiates roughly 100 billion times more energy than any known star could physically produce.

The leading explanation is far stranger: the glow may come from a rapidly feeding black hole buried inside an enormous, dense envelope of hydrogen.

Dark energy and quantum gravity may be deeply intertwined

For close to a century, physicists have pursued a way to unite gravity with quantum mechanics. Known as quantum gravity, this goal has remained frustratingly out of reach so far. Similarly elusive is the force of dark energy, which is believed to be driving the universe’s accelerating expansion.

But through new research published in Physical Review D, physicist Savvas Koushiappas of Brown University has proposed a new explanation suggesting that these two phenomena might not be separate at all. Instead, dark energy could be a natural side effect of quantum gravity, acting on the geometry of space itself.

Something Mysterious Just Passed Between Earth and a Distant Star

A mysterious object dubbed Phoebe may be a primordial black hole from the early universe, detected only because it briefly magnified the light of a distant star.

On the night of 18 December 2019, a star in our satellite galaxy, the Large Magellanic Cloud, briefly got brighter. Not dramatically nor explosively, just a smooth, symmetrical rise and fall in brightness lasting about an hour, as though something had passed in front of it and bent its light toward us. Then it returned to normal and was never seen to vary again.

That something has been named Phoebe. And working out what it actually is turns out to be one of the most intriguing puzzles in modern astronomy. The phenomenon at the heart of the story is called gravitational microlensing, and it’s one of the most elegant predictions of Einstein’s general theory of relativity.

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