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Category: cosmology

Astronomers trace a runaway star to a former companion’s supernova

Astronomers have strengthened long-standing predictions that massive runaway stars could have originated in binary pairs, and were dramatically ejected into space when their companion stars underwent supernova explosions. Through a combination of observations and stellar models, a team led by Baha Dinçel at the University of Jena in Germany revealed that the star HD 254577 likely did just this—and that its origins can be tied back to a companion whose remnants now form the Jellyfish nebula. The research is published in Astronomy & Astrophysics.

The Milky Way is embedded in a ‘large-scale sheet’ and this explains the motions of nearby galaxies

Computer simulations carried out by astronomers from the University of Groningen in collaboration with researchers from Germany, France and Sweden show that most of the (dark) matter beyond the Local Group of galaxies (which includes the Milky Way and the Andromeda Galaxy) must be organised in an extended plane. Above and below this plane are large voids. The observed motions of nearby galaxies and the joint masses of the Milky Way and the Andromeda Galaxy can only be properly explained with this ‘flat’ mass distribution. The research, led by PhD graduate Ewoud Wempe and Professor Amina Helmi, was published today in Nature Astronomy.

Almost a century ago, astronomer Edwin Hubble discovered that virtually all galaxies are moving away from the Milky Way. This is important evidence for the expansion of the universe and for the Big Bang. But even in Hubble’s time, it was clear that there were exceptions. For example, our neighbouring galaxy, Andromeda, is moving towards us at a speed of about 100 kilometres per second.

In fact, for half a century, astronomers have been wondering why most large nearby galaxies – with the exception of Andromeda – are moving away from us and do not seem to be affected by the mass and gravity of the so-called Local Group (the Milky Way, the Andromeda Galaxy and dozens of smaller galaxies).

Experiments Hint on Time Being an Illusion

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Hello and welcome! My name is Anton and in this video, we will talk about experimental evidence that time may be an illusion.
Links:
https://arxiv.org/pdf/2310.13386
https://journals.aps.org/prd/pdf/10.1103/qfns-48vq.
https://en.wikipedia.org/wiki/Problem_of_time.
https://journals.aps.org/prl/pdf/10.1103/5rtj-djfk.
https://journals.aps.org/prx/pdf/10.1103/PhysRevX.11.021029
https://journals.aps.org/prx/pdf/10.1103/PhysRevX.7.031022
#time #physics #universe.

0:00 Time — what is it?
1:20 Time in general relativity (Einstein)
2:10 Quantum mechanics time.
2:40 The problem of time.
3:30 Page Wootters mechanism — is time emergent?
5:00 Experiments and possible proofs — entropy and quantum dots.
7:40 Large scale system.
8:30 What this suggests and how black holes can help.
9:50 Conclusions.

Enjoy and please subscribe.

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Did we just see a black hole explode? Physicists think so—and it could explain (almost) everything

In 2023, a subatomic particle called a neutrino crashed into Earth with such a high amount of energy that it should have been impossible. In fact, there are no known sources anywhere in the universe capable of producing such energy—100,000 times more than the highest-energy particle ever produced by the Large Hadron Collider, the world’s most powerful particle accelerator. However, a team of physicists at the University of Massachusetts Amherst recently hypothesized that something like this could happen when a special kind of black hole, called a “quasi-extremal primordial black hole,” explodes.

In new research published in Physical Review Letters, the team not only accounts for the otherwise impossible neutrino but shows that the elementary particle could reveal the fundamental nature of the universe.

Supermassive black holes sit in ‘eye of their own storms,’ studies find

Gigantic black holes lurk at the center of virtually every galaxy, including ours, but we’ve lacked a precise picture of what impact they have on their surroundings. However, a University of Chicago-led group of scientists has used data from a recently launched satellite to reveal our clearest look yet into the boiling, seething gas surrounding two supermassive black holes, each located in the center of massive galaxy clusters.

“For the first time, we can directly measure the kinetic energy of the gas stirred by the black hole,” said Annie Heinrich, UChicago graduate student and among the lead authors on one of two papers on the findings, released in Nature. “It’s as though each supermassive black hole sits in the ‘eye of its own storm.’”

The readings came from the satellite XRISM, which was launched in 2023 by the Japanese Aerospace Exploration Agency in partnership with NASA and the European Space Agency. It has a unique ability to track the motions and read the chemical makeup of extremely hot, X-ray emitting gas in galaxy clusters.

Intercity quantum sensor network tightens axion dark matter constraints

Recently, scientists from institutions including the University of Science and Technology of China made a fundamental breakthrough in nuclear-spin quantum precision measurement. They developed the first intercity nuclear-spin-based quantum sensor network, which experimentally constrains the axion topological-defect dark matter and surpasses the astrophysical limits. The study is published in the journal Nature.

Current studies indicate that ordinary visible matter accounts for only about 4.9% of the universe, while dark matter makes up about 26.8%. Axions are among the best-motivated dark matter candidates, and axion fields can form topological defects during phase transitions in the early universe. As Earth crosses topological defects, the defects are expected to interact with nuclear spins and induce signals. However, detection remains a formidable challenge because signals are extremely weak and short-duration.

To overcome the detection challenge, the research team innovatively developed a nuclear-spin quantum precision measurement that “stores” microsecond-scale axion-induced signals in a long-lived nuclear-spin coherent state, enabling a minute-scale readout signal. At the same time, the team used nuclear spin as a quantum spin amplification to further enhance the weak dark-matter signal by at least 100-fold, increasing the sensitivity of spin rotation to about 1 μrad, representing an improvement of more than four orders of magnitude over previous techniques.

Gravitational wave signal tests Einstein’s theory of general relativity

For those who watch gravitational waves roll in from the universe, GW250114 is a big one. It’s the clearest gravitational wave signal from a binary black hole merger to date, and it gives researchers an opportunity to test Albert Einstein’s theory of gravity, known as general relativity.

“What’s fantastic is the event is pretty much identical to the first one we observed 10 years ago, GW150914. The reason it’s so much clearer is purely because our detectors have become much more accurate in the past 10 years,” said Cornell physicist Keefe Mitman, a NASA Hubble Postdoctoral Fellow at the Cornell Center for Astrophysics and Planetary Science in the College of Arts and Sciences.

Mitman is a co-author of the paper analyzing the wave, “Black Hole Spectroscopy and Tests of General Relativity with GW250114,” published in Physical Review Letters. It was written by the LIGO Scientific Collaboration, the Virgo Collaboration in Italy and the KAGRA Collaboration in Japan. Cornell researchers have been leading contributors to the LIGO-VIRGO-KAGRA project since its beginning in the early 1990s.

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