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Category: cosmology – Page 44

Scientists have now performed one such large-scale test by using DESI. They observed almost 6 million galaxies and quasars, which are bright hearts of galaxies powered by feeding supermassive black holes. Perhaps unsurprisingly, this test, which has traced the evolution of the universe since it was around 3 billion years old, has once again shown general relativity to be the right “recipe” for gravity.

“General relativity has been very well tested at the scale of solar systems, but we also needed to test that our assumption works at much larger scales,” study co-leader and the French National Center for Scientific Research (CNRS) cosmologist Pauline Zarrouk said in a statement. “Studying the rate at which galaxies formed lets us directly test our theories and, so far, we’re lining up with what general relativity predicts at cosmological scales.”

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Located a staggering 160,000 light-years from us, the star WOH G64 was imaged thanks to the impressive sharpness offered by the European Southern Observatory’s Very Large Telescope Interferometer (ESO’s VLTI). The new observations reveal a star puffing out gas and dust in the last stages before it becomes a supernova.

“For the first time, we have succeeded in taking a zoomed-in image of a in a galaxy outside our own Milky Way,” says Keiichi Ohnaka, an astrophysicist from Universidad Andrés Bello in Chile.

“We discovered an egg-shaped cocoon closely surrounding the star,” says Ohnaka, the lead author of a study reporting the observations published today in Astronomy & Astrophysics. “We are excited because this may be related to the drastic ejection of material from the dying star before a supernova explosion.”

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For decades, scientists have used the Milky Way as a model for understanding how galaxies form. But three new studies raise questions about whether the Milky Way is truly representative of other galaxies in the universe.

“The Milky Way has been an incredible physics laboratory, including for the physics of galaxy formation and the physics of dark matter,” said Risa Wechsler, the Humanities and Sciences Professor and professor of physics in the School of Humanities and Sciences. “But the Milky Way is only one system and may not be typical of how other galaxies formed. That’s why it’s critical to find similar galaxies and compare them.”

To achieve that goal, Wechsler cofounded the Satellites Around Galactic Analogs (SAGA) Survey dedicated to comparing galaxies similar in mass to the Milky Way.

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New research into dark matter suggests it might have originated from a “Dark Big Bang,” distinct from the traditional Big Bang.

This theory, which posits a separate cosmic event as the source of dark matter, could change how we understand the universe’s early moments. Upcoming gravitational wave detection experiments could provide critical evidence to support this theory.

Alternative theory of dark matter genesis.

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Gravity has shaped our cosmos. Its attractive influence turned tiny differences in the amount of matter present in the early universe into the sprawling strands of galaxies we see today. A new study using data from the Dark Energy Spectroscopic Instrument (DESI) has traced how this cosmic structure grew over the past 11 billion years, providing the most precise test to date of gravity at very large scales.

DESI is an international collaboration of more than 900 researchers from over 70 institutions around the world and is managed by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).

In their new study, DESI researchers found that gravity behaves as predicted by Einstein’s theory of general relativity. The result validates the leading model of the universe and limits possible theories of modified gravity, which have been proposed as alternative ways to explain unexpected observations—including the accelerating expansion of our universe that is typically attributed to dark energy.

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Astronomers at the University of Toronto (U of T) have discovered the first pairs of white dwarf and main sequence stars—” dead” remnants and “living” stars—in young star clusters. Described in a new study published in The Astrophysical Journal, this breakthrough offers new insights into an extreme phase of stellar evolution, and one of the biggest mysteries in astrophysics.

Scientists can now begin to bridge the gap between the earliest and final stages of binary star systems—two stars that orbit a shared center of gravity—to further our understanding of how stars form, how galaxies evolve, and how most elements on the periodic table were created. This discovery could also help explain cosmic events like supernova explosions and gravitational waves, since binaries containing one or more of these compact dead stars are thought to be the origin of such phenomena.

Most stars exist in binary systems. In fact, nearly half of all stars similar to our sun have at least one companion star. These paired stars usually differ in size, with one star often being more massive than the other. Though one might be tempted to assume that these stars evolve at the same rate, more massive stars tend to live shorter lives and go through the stages of stellar evolution much faster than their lower mass companions.

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Astounding simulation shows magnetic fields create fluffy, not flat, accretion disks around supermassive black holes, altering our understanding of black hole dynamics.

A team of astrophysicists from Caltech has achieved a groundbreaking milestone by simulating the journey of primordial gas from the early universe to its incorporation into a disk of material feeding a supermassive black hole. This innovative simulation challenges theories about these disks that have persisted since the 1970s and opens new doors for understanding the growth and evolution of black holes and galaxies.

“Our new simulation marks the culmination of several years of work from two large collaborations started here at Caltech,” says Phil Hopkins, the Ira S. Bowen Professor of Theoretical Astrophysics.

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Then, in the 1980s, neutrinos from this supernova were picked up by the Irvine-Michigan-Brookhaven detector deep underground in Ohio. The discovery marked one of the first measurements of neutrinos from beyond our solar system, helped kickstart the field of observational neutrino astronomy, and provided a starting point that next-generation neutrino detectors continue to build on.

But the discovery was also lucky: The detector was built primarily to study proton decay, rather than neutrinos. “When you build a new detector with new capabilities, you’re sensitive to things that you never expected,” says Henry Sobel, a physics professor at the University of California, Irvine, and one of IMB’s original collaborators. The unexpected supernova would shape the legacy of IMB, which was recently recognized as an APS Historic Site for its role in neutrino science.

In the mid-1970s, teams of physicists were racing to build detectors that could measure proton decay, a hypothesized phenomenon that would confirm Howard Georgi and Sheldon Glashow’s new Grand Unified Theory, one that sought to unite three of the four fundamental forces of nature. The winner emerged in Painesville, Ohio, a small city northeast of Cleveland: The IMB detector, the world’s first kiloton-scale nucleon decay detector, began collecting data in 1982.

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Researchers use the H.E.S.S. Observatory to overcome the challenge of detecting high-energy cosmic-ray electrons and positrons, revealing their likely origins close to our solar system through advanced data analysis techniques.

The Universe is filled with extreme environments, from the coldest regions to the most energetic sources imaginable. These conditions give rise to extraordinary objects like supernova remnants, pulsars, and active galactic nuclei, which emit charged particles and gamma rays with energies far exceeding those produced by the nuclear fusion processes in stars—by several orders of magnitude.

Challenges in Cosmic Ray Detection.

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Black holes are one of the most enigmatic stellar objects. While best known for swallowing up their surroundings into a gravity pit from which nothing can escape, they can also shoot off powerful jets of charged particles, leading to explosive bursts of gamma rays that can release more energy in mere seconds than our sun will emit in its entire lifetime.

For such a spectacular event to occur, a black hole needs to carry a powerful . Where this magnetism comes from, however, has been a long-standing mystery.

Using calculations of black hole formation, scientists at the Flatiron Institute and their collaborators have finally found the origin of those magnetic fields: the collapsing parent stars of the themselves. The researchers report their results November 18 in The Astrophysical Journal Letters.

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