| Dec 08, 2022 |
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(Nanowerk Information) The mysteries of the cosmos proceed to amaze astronomers, and with every new remark comes an opportunity to deepen – or upend – our understanding of the universe.
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Within the journal Nature (“A protracted-duration gamma-ray burst with a peculiar origin”), a world crew of astrophysicists report the invention of a novel cosmological gamma-ray burst (GRB) that defies prevailing theories of how the violent cosmic explosions kind. This “oddball” burst led the crew to suggest a brand new mannequin, or supply, for sure varieties of GRBs.
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Gamma-ray bursts are essentially the most luminous and violent explosions within the universe. They signify the deaths of stars or collisions of stellar remnants. Noticed GRBs are sometimes positioned into two classes: short- or long-duration GRBs. Lengthy GRBs originate from the deaths of huge stars, and are sometimes related to vibrant optical transients named supernovae. Quick GRBs have a period of lower than two seconds and originate from the collisions of two neutron stars or a neutron star and a black gap, and are sometimes related to extra faint optical transients generally known as kilonovae.
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| A protracted-duration gamma-ray burst noticed in late 2021 revealed signatures sometimes related to short-duration bursts, forcing puzzled scientists to create a brand new mannequin for the origin of this distinctive burst.
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For many years, GRBs nestled properly into these cozy classes. Till now.
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On Dec.11, 2021, a GRB triggered a number of gamma-ray detectors in area, together with NASA’s Fermi Gamma-ray Telescope and the Neil Gehrels Swift Observatory. This burst, with a period of almost 70 seconds, would sometimes be considered a standard lengthy GRB. That’s, till a number of groups from the U.S. and Europe carried out follow-up observations and found a shocking signature.
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“This GRB consists of two elements: a 13-second lengthy laborious spike and a 55-second softer prolonged emission,” mentioned UNLV alumnus and research corresponding writer Bin-Bin Zhang, who’s at the moment with China’s Nanjing College. “The period of the 13-second laborious spike ought to have utterly excluded this burst from the quick GRB class.”
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In different phrases, as a substitute of displaying a a lot brighter supernova, as anticipated, the remark was according to a kilonova that’s extra sometimes related to a brief GRB.
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“Such a peculiar GRB was the primary of its type ever detected,” mentioned UNLV astrophysics professor Bing Zhang, co-corresponding-author of the Nature paper. “This discovery not solely challenged our understanding of GRB origins, it additionally requires us to think about a brand new mannequin for a way some GRBs kind.”
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The analysis crew believes that this distinctive GRB, generally known as GRB 211211A, possible fashioned by collision between a neutron star and a white dwarf, what’s generally known as a WD-NS merger.
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White dwarfs are earth-sized objects that kind from the dying of low-mass stars – these with a mass smaller than that of about eight of our Suns. Neutron stars kind when extra huge stars, these with a mass of between about eight and 20 Suns, die off. When even bigger stars die, they kind black holes immediately.
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Huge, low-density stars make long-duration GRBs whereas high-density stars, together with neutron stars, make quick period GRBs. In line with UNLV’s Zhang, white dwarfs have intermediate densities, which make them splendid origins for the kind of GRB found in 2021 because it shows an intermediately lengthy period with out involving a large star.
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“Regardless of the comparatively giant variety of GRBs noticed annually, the distinctive signature of GRB 211211A pushed the envelope of our present categorial programs and required a brand new mind-set,” mentioned Zhang. “After cautious evaluation, the one merger state of affairs that made sense was that of a white dwarf and neutron star.”
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UNLV doctoral scholar Shunke Ai and a scholar from Nanjing College collaborated to develop an in depth mannequin to interpret the peculiar kilonova signature noticed by GRB 211211A. Ai discovered that if a WD-NS merger leaves behind a quickly spinning neutron star, generally known as a magnetar, the extra power injection from the magnetar mixed with the nuclear response power from the fabric thrown through the burst can account for the kilonova emission noticed for GRB 211211A.
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