MSGID: 1:317/3 6274a48b   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Hubble reveals surviving companion star in aftermath of supernova    
    The discovery helps explain the puzzle of hydrogen loss pre-supernova,   
   and supports the theory that most massive stars are paired.    
      
     Date:   
         May 5, 2022   
     Source:   
         NASA/Goddard Space Flight Center   
     Summary:   
         It's not unheard of to find a surviving star at the scene of a   
         titanic supernova explosion, which would be expected to obliterate   
         everything around it, but new research has provided a long-awaited   
         clue to a specific type of stellar death. In some supernova cases,   
         astronomers find no trace of the former star's outermost layer of   
         hydrogen. What happened to the hydrogen? Suspicions that companion   
         stars are responsible - - siphoning away their partners' outer shell   
         before their death -- are supported by the recent identification   
         of a surviving companion star on the scene of supernova 2013ge.   
      
      
      
   FULL STORY   
   ==========================================================================   
   It's not unheard of to find a surviving star at the scene of a titanic   
   supernova explosion, which would be expected to obliterate everything   
   around it, but the latest research from the Hubble Space Telescope has   
   provided a long-awaited clue to a specific type of stellar death. In   
   some supernova cases, astronomers find no trace of the former star's   
   outermost layer of hydrogen.   
      
   What happened to the hydrogen? Suspicions that companion stars are   
   responsible -- siphoning away their partners' outer shell before their   
   death -- are supported by Hubble's identification of a surviving companion   
   star on the scene of supernova 2013ge.   
      
      
   ==========================================================================   
   The discovery also lends support to the theory that the majority of   
   massive stars form and evolve as binary systems. It could also be   
   the prequel to another cosmic drama: In time, the surviving, massive   
   companion star will also undergo a supernova, and if both the stars'   
   remnant cores are not flung from the system, they will eventually merge   
   and produce gravitational waves, shaking the fabric of space itself.   
      
   NASA's Hubble Space Telescope has uncovered a witness at the scene of a   
   star's explosive death: a companion star previously hidden in the glare   
   of its partner's supernova. The discovery is a first for a particular   
   type of supernova -- one in which the star was stripped of its entire   
   outer gas envelope before exploding.   
      
   The finding provides crucial insight into the binary nature of massive   
   stars, as well as the potential prequel to the ultimate merger of the   
   companion stars that would rattle across the universe as gravitational   
   waves, ripples in the fabric of spacetime itself.   
      
   Astronomers detect the signature of various elements in supernova   
   explosions.   
      
   These elements are layered like an onion pre-supernova. Hydrogen is found   
   in the outermost layer of a star, and if no hydrogen is detected in the   
   aftermath of the supernova, that means it was stripped away before the   
   explosion occurred.   
      
   The cause of the hydrogen loss had been a mystery, and astronomers have   
   been using Hubble to search for clues and test theories to explain these   
   stripped supernovae. The new Hubble observations provide the best evidence   
   yet to support the theory that an unseen companion star siphons off the   
   gas envelope from its partner star before it explodes.   
      
      
      
   ==========================================================================   
   "This was the moment we had been waiting for, finally seeing the evidence   
   for a binary system progenitor of a fully stripped supernova," said   
   astronomer Ori Fox of the Space Telescope Science Institute in Baltimore,   
   Maryland, lead investigator on the Hubble research program. "The goal is   
   to move this area of study from theory to working with data and seeing   
   what these systems really look like."  Fox's team used Hubble's Wide   
   Field Camera 3 to study the region of supernova (SN) 2013ge in ultraviolet   
   light, as well as previous Hubble observations in the Barbara A. Mikulski   
   Archive for Space Telescopes. Astronomers saw the light of the supernova   
   fading over time from 2016 to 2020 -- but another nearby source of   
   ultraviolet light at the same position maintained its brightness.   
      
   This underlying source of ultraviolet emission is what the team proposes   
   is the surviving binary companion to SN 2013ge.   
      
   Two by two?  Previously, scientists theorized that a massive progenitor   
   star's strong winds could blow away its hydrogen gas envelope, but   
   observational evidence didn't support that. To explain the disconnect,   
   astronomers developed theories and models in which a binary companion   
   siphons off the hydrogen.   
      
   "In recent years many different lines of evidence have told us that   
   stripped supernovae are likely formed in binaries, but we had yet to   
   actually see the companion. So much of studying cosmic explosions is   
   like forensic science - - searching for clues and seeing what theories   
   match. Thanks to Hubble, we are able to see this directly," said Maria   
   Drout of the University of Toronto, a member of the Hubble research team.   
      
      
      
   ==========================================================================   
   In prior observations of SN 2013ge, Hubble saw two peaks in the   
   ultraviolet light, rather than just the one typically seen in most   
   supernovae. Fox said that one explanation for this double brightening was   
   that the second peak shows when the supernova's shock wave hit a companion   
   star, a possibility that now seems much more likely. Hubble's latest   
   observations indicate that while the companion star was significantly   
   jostled, including the hydrogen gas it had siphoned off its partner,   
   it was not destroyed. Fox likens the effect to a jiggling bowl of jelly,   
   which will eventually settle back to its original form.   
      
   While additional confirmation and similar supporting discoveries need   
   to be found, Fox said that the implications of the discovery are still   
   substantial, lending support to theories that the majority of massive   
   stars form and evolve as binary systems.   
      
   One to Watch Unlike supernovae that have a puffy shell of gas to light   
   up, the progenitors of fully stripped-envelope supernovae have proven   
   difficult to identify in pre- explosion images. Now that astronomers   
   have been lucky enough to identify the surviving companion star, they   
   can use it to work backward and determine characteristics of the star   
   that exploded, as well as the unprecedented opportunity to watch the   
   aftermath unfold with the survivor.   
      
   As a massive star itself, SN 2013ge's companion is also destined to   
   undergo a supernova. Its former partner is now likely a compact object,   
   such as a neutron star or black hole, and the companion will likely go   
   that route as well.   
      
   The closeness of the original companion stars will determine if they   
   stay together. If the distance is too great, the companion star will be   
   flung out of the system to wander alone across our galaxy, a fate that   
   could explain many seemingly solitary supernovae.   
      
   However, if the stars were close enough to each other pre-supernova, they   
   will continue orbiting each other as black holes or neutron stars. In   
   that case, they would eventually spiral toward each other and merge,   
   creating gravitational waves in the process.   
      
   That is an exciting prospect for astronomers, as gravitational waves   
   are a branch of astrophysics that has only begun to be explored. They   
   are waves or ripples in the fabric of spacetime itself, predicted by   
   Albert Einstein in the early 20th century. Gravitational waves were   
   first directly observed by the Laser Interferometer Gravitational-Wave   
   Observatory.   
      
   "With the surviving companion of SN 2013ge, we could potentially be seeing   
   the prequel to a gravitational wave event, although such an event would   
   still be about a billion years in the future," Fox said.   
      
   Fox and his collaborators will be working with Hubble to build up a larger   
   sample of surviving companion stars to other supernovae, in effect giving   
   SN 2013ge some company again.   
      
   "There is great potential beyond just understanding the supernova   
   itself. Since we now know most massive stars in the universe form in   
   binary pairs, observations of surviving companion stars are necessary to   
   help understand the details behind binary formation, material-swapping,   
   and co-evolutionary development. It's an exciting time to be studying   
   the stars," Fox said.   
      
   "Understanding the lifecycle of massive stars is particularly important   
   to us because all heavy elements are forged in their cores and through   
   their supernovae. Those elements make up much of the observable universe,   
   including life as we know it," added co-author Alex Filippenko of the   
   University of California at Berkeley.   
      
      
   ==========================================================================   
   Story Source: Materials provided by   
   NASA/Goddard_Space_Flight_Center. Note: Content may be edited for style   
   and length.   
      
      
   ==========================================================================   
   Related Multimedia:   
       * Supernova_2013ge_with_its_companion_star   
   ==========================================================================   
   Journal Reference:   
      1. Ori D. Fox, Schuyler D. Van Dyk, Benjamin F. Williams, Maria Drout,   
         Emmanouil Zapartas, Nathan Smith, Dan Milisavljevic, Jennifer   
         E. Andrews, K. Azalee Bostroem, Alexei V. Filippenko, Sebastian   
         Gomez, Patrick L.   
      
         Kelly, S. E. de Mink, Justin Pierel, Armin Rest, Stuart   
         Ryder, Niharika Sravan, Lou Strolger, Qinan Wang, Kathryn   
         E. Weil. The Candidate Progenitor Companion Star of the Type   
         Ib/c SN 2013ge. The Astrophysical Journal Letters, 2022; 929 (1):   
         L15 DOI: 10.3847/2041-8213/ac5890   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2022/05/220505114702.htm   
      
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