MSGID: 1:317/3 64951fe6   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Never-before-seen way to annihilate a star    
      
     Date:   
         June 22, 2023   
     Source:   
         Association of Universities for Research in Astronomy (AURA)   
     Summary:   
         Astronomers studying a powerful gamma-ray burst, may have detected   
         a never-before-seen way to destroy a star. Unlike most GRBs,   
         which are caused by exploding massive stars or the chance mergers   
         of neutron stars, astronomers have concluded that this GRB came   
         instead from the collision of stars or stellar remnants in the   
         jam-packed environment surrounding a supermassive black hole at   
         the core of an ancient galaxy.   
      
      
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   FULL STORY   
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   International Gemini Observatory traces gamma-ray burst to nucleus   
   of ancient galaxy, suggesting stars can undergo demolition-derby-like   
   collisions.   
      
   Astronomers studying a powerful gamma-ray burst (GRB) with the   
   Gemini South telescope, operated by NSF's NOIRLab, may have detected   
   a never-before-seen way to destroy a star. Unlike most GRBs, which are   
   caused by exploding massive stars or the chance mergers of neutron stars,   
   astronomers have concluded that this GRB came instead from the collision   
   of stars or stellar remnants in the jam-packed environment surrounding   
   a supermassive black hole at the core of an ancient galaxy.   
      
   Most stars in the Universe die in predictable ways, depending on their   
   mass.   
      
   Relatively low-mass stars like our Sun slough off their outer layers in   
   old age and eventually fade to become white dwarf stars. More massive   
   stars burn brighter and die sooner in cataclysmic supernova explosions,   
   creating ultradense objects like neutron stars and black holes. If two   
   such stellar remnants form a binary system, they also can eventually   
   collide. New research, however, points to a long-hypothesized, but   
   never-before-seen, fourth option.   
      
   While searching for the origins of a long-duration gamma-ray burst   
   (GRB), astronomers using the Gemini South telescope in Chile, part of   
   the International Gemini Observatory operated by NSF's NOIRLab, and   
   other telescopes [1], have uncovered evidence of a demolition-derby-like   
   collision of stars or stellar remnants in the chaotic and densely packed   
   region near an ancient galaxy's supermassive black hole.   
      
   "These new results show that stars can meet their demise in some of the   
   densest regions of the Universe where they can be driven to collide," said   
   Andrew Levan, an astronomer with Radboud University in The Netherlands and   
   lead author of a paper appearing in the journal Nature Astronomy. "This   
   is exciting for understanding how stars die and for answering other   
   questions, such as what unexpected sources might create gravitational   
   waves that we could detect on Earth."  Ancient galaxies are long past   
   their star-forming prime and would have few, if any, remaining giant   
   stars, the principal source of long GRBs. Their cores, however, are   
   teeming with stars and a menagerie of ultra-dense stellar remnants,   
   such as white dwarf stars, neutron stars, and black holes.   
      
   Astronomers have long suspected that in the turbulent beehive of activity   
   surrounding a supermassive black hole, it would only be a matter of time   
   until two stellar objects collide to produce a GRB. Evidence for that   
   type of merger, however, has been elusive.   
      
   The first hints that such an event had occurred were seen on 19 October   
   2019 when NASA's Neil Gehrels Swift Observatory detected a bright flash of   
   gamma rays that lasted for a little more than one minute. Any GRB lasting   
   more than two seconds is considered "long." Such bursts typically come   
   from the supernova death of stars at least 10 times the mass of our Sun --   
   but not always.   
      
   The researchers then used Gemini South to make long-term observations   
   of the GRB's fading afterglow to learn more about its origins. The   
   observations allowed the astronomers to pinpoint the location of   
   the GRB to a region less than 100 light-years from the nucleus of an   
   ancient galaxy, which placed it very near the galaxy's supermassive black   
   hole. The researchers also found no evidence of a corresponding supernova,   
   which would leave its imprint on the light studied by Gemini South.   
      
   "Our follow-up observation told us that rather than being a massive   
   star collapsing, the burst was most likely caused by the merger of two   
   compact objects," said Levan. "By pinpointing its location to the center   
   of a previously identified ancient galaxy, we had the first tantalizing   
   evidence of a new pathway for stars to meet their demise."  In normal   
   galactic environments, the production of long GRBs from colliding   
   stellar remnants such as neutron stars and black holes is thought to be   
   vanishingly rare. The cores of ancient galaxies, however, are anything   
   but normal and there may be a million or more stars crammed into a region   
   just a few light-years across. Such extreme population density may be   
   great enough that occasional stellar collisions can occur, especially   
   under the titanic gravitational influence of a supermassive black hole,   
   which would perturb the motions of stars and send them careening in   
   random directions. Eventually, these wayward stars would intersect and   
   merge, triggering a titanic explosion that could be observed from vast   
   cosmic distances.   
      
   It is possible that such events occur routinely in similarly crowded   
   regions across the Universe but have gone unnoticed until this point. A   
   possible reason for their obscurity is that galactic centers are brimming   
   with dust and gas, which could obscure both the initial flash of the   
   GRB and the resulting afterglow. This particular GRB, identified as GRB   
   191019A, may be a rare exception, allowing astronomers to detect the   
   burst and study its after effects.   
      
   The researchers would like to discover more of these events. Their hope   
   is to match a GRB detection with a corresponding gravitational-wave   
   detection, which would reveal more about their true nature and confirm   
   their origins, even in the murkiest of environments. The Vera C. Rubin   
   Observatory, when it comes online in 2025, will be invaluable in this   
   kind of research.   
      
   "Studying gamma-ray bursts like these is a great example of how the   
   field is really advanced by many facilities working together, from the   
   detection of the GRB, to the discoveries of afterglows and distances   
   with telescopes like Gemini, through to detailed dissection of events   
   with observations across the electromagnetic spectrum," said Levan.   
      
   "These observations add to Gemini's rich heritage developing our   
   understanding of stellar evolution," says Martin Still, NSF's program   
   director for the International Gemini Observatory. "The time sensitive   
   observations are a testament to Gemini's nimble operations and sensitivity   
   to distant, dynamic events across the Universe."   
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Black_Holes # Stars # Galaxies # Astrophysics #   
                   Nebulae # Astronomy # Cosmic_Rays # Space_Telescopes   
       * RELATED_TERMS   
             o Supernova o Chandra_X-ray_Observatory o Blue_supergiant_star o   
             Interstellar_medium o Spitzer_space_telescope o Globular_cluster   
             o Gravitational_wave o Astronomy   
      
   ==========================================================================   
   Story Source: Materials provided by   
   Association_of_Universities_for_Research_in_Astronomy_ (AURA). Note:   
   Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Levan, A. J., Malesani, D. B., Gompertz, B. P., et al. A   
      long-duration   
         gamma-ray burst of dynamical origin from the nucleus of an ancient   
         galaxy. Nature Astronomy, 2023 DOI: 10.1038/s41550-023-01998-8   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230622120817.htm   
      
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