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Category: cosmology – Page 75

University of Copenhagen astrophysicists help explain a mysterious phenomenon, whereby stars suddenly vanish from the night sky. Their study of an unusual binary star system has resulted in convincing evidence that massive stars can completely collapse and become black holes without a supernova explosion.

One day, the star at the center of our own solar system, the Sun, will begin to expand until it engulfs Earth. It will then become increasingly unstable until it eventually contracts into a small and dense object known as a white dwarf.

However, if the Sun were of a weight class roughly eight times greater or more, it would probably go out with a huge bang — as a supernova. Its collapse would culminate into an explosion, ejecting energy and mass into space with enormous force, prior to leaving behind a neutron star or a black hole in its wake.

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In research published earlier this year, physicists from the University of Hyderabad in India say they’re on the path to solving one of the universe’s biggest outstanding problems. Since Edwin Hubble realized the universe is always expanding nearly 100 years ago, scientists have used the “Hubble constant” in calculations on virtually every scale in the universe. But today, estimates for the Hubble constant don’t always align, with a difference of up to 10 percent between calculations made using different methods. (When someone at NASA mixes up meters and yards and loses an entire spacecraft, that’s not even a full 10 percent deviation.)

The paper appears in the peer reviewed journal Classical and Quantum Gravity. The journal has an ongoing, periodically updated “focus issue” specifically about this measurement tension, and the editors explain the problem there—scientists can’t say for sure that the different Hubble constants measured are actually different, rather than just observation or calibration issues.

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From Rice University

4.5.24 Silvia Cernea Clark 713−348−6728 [email protected].

Chris Stipes 713−348−6778 [email protected].

If you were to throw a message in a bottle into a black hole, all of the information in it, down to the quantum level, would become completely scrambled. Because in black holes this scrambling happens as quickly and thoroughly as quantum mechanics allows, they are generally considered nature’s ultimate information scramblers.

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The JADES Deep Field uses observations taken by NASA’s James Webb Space Telescope (JWST) as part of the JADES (JWST Advanced Deep Extragalactic Survey) program. A team of astronomers studying JADES data identified about 80 objects (circled in green) that changed in brightness over time. Most of these objects, known as transients, are the result of exploding stars or supernovae. Credit: NASA, ESA, CSA, STScI, JADES Collaboration.

Peering deeply into the cosmos, NASA’s James Webb Space Telescope is providing scientists with their first detailed glimpse of supernovae from a time when our universe was just a small fraction of its current age. A team using Webb data has identified 10 times more supernovae in the early universe than were previously known. A few of the newfound exploding stars are the most distant examples of their type, including those used to measure the universe’s expansion rate.

“Webb is a supernova discovery machine,” said Christa DeCoursey, a third-year graduate student at the Steward Observatory and the University of Arizona in Tucson. “The sheer number of detections plus the great distances to these supernovae are the two most exciting outcomes from our survey.”

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Clouds of gas in a distant galaxy are being pushed faster and faster—at more than 10,000 miles per second—out among neighboring stars by blasts of radiation from the supermassive black hole at the galaxy’s center. It’s a discovery that helps illuminate the way active black holes can continuously shape their galaxies by spurring on or snuffing out the development of new stars.

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Astronomers, with the help of the Hubble telescope, have now detected a rare intermediate-size black hole.

This black hole is hiding the Earth’s cosmic backyard at a distance of 6,000 light-years away within a globular star cluster.

The iconic Hubble Space Telescope has been used by astronomers to observe a compact region of space which has a mass of 800 Suns and is likely to be a black hole.

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The Higgs boson has an extremely short lifespan, living for about 10–22 seconds before quickly decaying into other particles. For comparison, in that brief time, light can only travel about the width of a small atomic nucleus. Scientists study the Higgs boson by detecting its decay products in particle collisions at the Large Hadron Collider. But what if the Higgs boson could also decay into unexpected new particles that are long-lived? What if these particles can travel a few centimeters through the detector before they decay? These long-lived particles (LLPs) could shed light on some of the universe’s biggest mysteries, such as the reason matter prevailed over antimatter in the early universe and the nature of dark matter. Searching for LLPs is extremely challenging because they rarely interact with matter, making them difficult to observe in a particle detector. However, their unusual signatures provide exciting prospects for discovery. Unlike particles that leave a continuous track, LLPs result in noticeable displacements between their production and decay points within the detector. Identifying such a signature requires dedicated algorithms. In a new study submitted to Physical Review Letters, ATLAS scientists used a new algorithm to search for LLPs produced in the decay of Higgs bosons. Boosting sensitivity with a new algorithm Figure 1: A comparison of the radial distributions of reconstructed displaced vertices in a simulated long-lived particle (LLP) sample using the legacy and new (updated) track reconstruction configurations. The circular markers represent reconstructed vertices that are matched to LLP decay vertices and the dashed lines represent reconstructed vertices from background decay vertices (non-LLP). (Image: ATLAS Collaboration/CERN) Despite being critical to the LLP searches, dedicated reconstruction algorithms were previously so resource intensive that they could only be applied to less than 10% of all recorded ATLAS data. Recently, however, ATLAS scientists implemented a new “Large-Radius Tracking” algorithm (LRT), which significantly speeds up the reconstruction of charged particle trajectories in the ATLAS Inner Detector that do not point back to the primary proton-proton collision point, while drastically reducing backgrounds and random combinations of detector signals. The LRT algorithm is executed after the primary tracking iteration using exclusively the detector hits (energy deposits from charged particles recorded in individual detector elements) not already assigned to primary tracks. As a result, ATLAS saw an enormous increase in the efficiency of identifying LLP decays (see Figure 1). The new algorithm also improved CPU processing time more than tenfold compared to the legacy implementation, and the disk space usage per event was reduced by more than a factor of 50. These improvements enabled physicists to fully integrate the LRT algorithm into the standard ATLAS event reconstruction chain. Now, every recorded collision event can be scrutinized for the presence of new LLPs, greatly enhancing the discovery potential of such signatures. Physicists are searching for Higgs bosons decaying into new long-lived particles, which may leave a ‘displaced’ signature in the ATLAS detector. Exploring the dark with the Higgs boson Figure 2: Observed 95% confidence-limit on the decay of the Higgs boson to a pair of long-lived s particles that decay back to Standard-Model particles shown as a function of the mean proper decay length ( of the long-lived particle. The observed limits for the Higgs Portal model from the previous ATLAS search are shown with the dotted lines. (Image: ATLAS Collaboration/CERN) In their new result, ATLAS scientists employed the LRT algorithm to search for LLPs that decay hadronically, leaving a distinct signature of one or more hadronic “jets” of particles originating at a significantly displaced position from the proton–proton collision point (a displaced vertex). Physicists also focused on the Higgs “portal” model, in which the Higgs boson mediates interactions with dark-matter particles through its coupling to a neutral boson s, resulting in exotic decays of the Higgs boson to a pair of long-lived s particles that decay into Standard-Model particles. The ATLAS team studied collision events with unique characteristics consistent with the production of the Higgs boson. The background processes that mimic the LLP signature are complex and challenging to model. To achieve good discrimination between signal and background processes, ATLAS physicists used a machine learning algorithm trained to isolate events with jets arising from LLP decays. Complementary to this, a dedicated displaced vertex reconstruction algorithm was used to pinpoint the origin of hadronic jets originating from the decay of LLPs. This new search did not uncover any events featuring Higgs-boson decays to LLPs. It improves bounds on Higgs-boson decays to LLPs by a factor of 10 to 40 times compared to the previous search using the exact same dataset (see Figure 2)! For the first time at the LHC, bounds on exotic decays of the Higgs boson for low LLP masses (less than 16 GeV) have surpassed results for direct searches of exotic Higgs-boson decays to undetected states. About the event display: A 13 TeV collision event recorded by the ATLAS experiment containing two displaced decay vertices (blue circles) significantly displaced from the beam line showing “prompt” non displaced decay vertices (pink circles). The event characteristics are compatible with what would be expected if a Higgs boson is produced in association with a Z boson (decaying to two electrons indicated by green towers), and decayed into two LLPs (decaying into two b-quarks each). Tracks shown in yellow and jets are indicated by cones. The green and yellow blocks correspond to energy deposition in the electromagnetic and hadronic calorimeters, respectively. (Image: ATLAS Collaboration/CERN) Learn more Search for light long-lived particles in proton-proton collisions at 13 TeV using displaced vertices in the ATLAS inner detector (Submitted to PRL, arXiv:2403.15332, see figures) Performance of the reconstruction of large impact parameter tracks in the inner detector of ATLAS (Eur. Phys. J. C 83 (2023) 1,081, arXiv:2304.12867, see figures) Search for exotic decays of the Higgs boson into long-lived particles in proton-proton collisions at 13 TeV using displaced vertices in the ATLAS inner detector (JHEP 11 (2021) 229, arXiv:2107.06092, see figures)

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Quantum field theory reveals potential flaws in models predicting numerous primordial black holes, suggesting fewer exist, which may impact theories of dark matter and the universe’s structure.

Researchers have applied the well-understood and highly verified quantum field theory, usually applied to the study of the very small, to a new target, the early universe. Their exploration led to the conclusion that there ought to be far fewer miniature black holes than most models suggest, though observations to confirm this should soon be possible. The specific kind of black hole in question could be a contender for dark matter.

The study, which was published recently in Physical Review Letters, was conducted by researchers at the Research Center for the Early Universe (RESCEU) and Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI) at the University of Tokyo.

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The DESI collaboration is conducting a groundbreaking experiment to understand the universe’s expansion and acceleration. Their work with the DESI instrument has enabled them to map the cosmos from its early stages to the present, challenging existing models of the universe. Initial findings suggest there may be more to discover about dark energy and cosmic acceleration. The project’s innovative approach, including a fully blinded analysis, ensures that their conclusions are based on unbiased data, paving the way for future discoveries in astrophysics. Credit: SciTechDaily.com.

The DESI collaboration is examining the universe’s accelerating expansion through comprehensive mapping from its early stages to the present. Their findings challenge traditional cosmic models and suggest new insights into dark energy, all while utilizing groundbreaking, unbiased research methods.

A team of researchers, including an astrophysicist from The University of Texas at Dallas, as part of the Dark Energy Spectroscopic Instrument (DESI) collaboration, is leading a groundbreaking experiment aimed at exploring the universe’s expansion and acceleration.

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