MSGID: 1:317/3 6448a8e2   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Medium-sized black holes eat stars like messy toddlers    
    Elusive intermediate-mass black holes take a few bites, then eject the   
   leftovers    
      
     Date:   
         April 25, 2023   
     Source:   
         Northwestern University   
     Summary:   
         In new 3D computer simulations, astrophysicists modeled black holes   
         of varying masses and then hurled stars (about the size of our sun)   
         past them to see what might happen. If they exist, intermediate-mass   
         black holes likely devour wayward stars like a messy toddler --   
         taking a few bites and then flinging the remains across the galaxy.   
      
      
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   FULL STORY   
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   If they exist, intermediate-mass black holes likely devour wayward stars   
   like a messy toddler -- taking a few bites and then flinging the remains   
   across the galaxy -- a new Northwestern University-led study has found.   
      
   In new 3D computer simulations, astrophysicists modeled black holes of   
   varying masses and then hurled stars (about the size of our sun) past   
   them to see what might happen.   
      
   When a star approaches an intermediate-mass black hole, it initially   
   gets caught in the black hole's orbit, the researchers discovered. After   
   that, the black hole begins its lengthy and violent meal. Every time the   
   star makes a lap, the black hole takes a bite -- further cannibalizing   
   the star with each passage. Eventually, nothing is left but the star's   
   misshapen and incredibly dense core.   
      
   At that point, the black hole ejects the remains. The star's remnant   
   flies to safety across the galaxy.   
      
   Not only do these new simulations hint at the unknown behaviors of   
   intermediate-mass black holes, they also provide astronomers with new   
   clues to help finally pinpoint these hidden giants within our night sky.   
      
   "We obviously cannot observe black holes directly because they don't   
   emit light," said Northwestern's Fulya Kıroğlu, who led the   
   study. "So, instead, we have to look at the interactions between black   
   holes and their environments. We found that stars undergo multiple   
   passages before being ejected. After each passage, they lose more mass,   
   causing a flair of light as its ripped apart. Each flare is brighter than   
   the last, creating a signature that might help astronomers find them."   
   Kıroğlu will present this research during the virtual portion   
   of the American Physical Society's (APS) April meeting. "Tidal disruption   
   events of stars by intermediate-mass black holes" will take place on April   
   25, as a part of the session "Medium: Cosmic Rays, AGN & Galaxies." . The   
   Astrophysical Journal has accepted the study for publication.   
      
   Kıroğlu is an astrophysics graduate student at Northwestern's   
   Weinberg College of Arts and Sciences and member of the Center for   
   Interdisciplinary Exploration and Research in Astrophysics (CIERA). She is   
   advised by paper co-author Frederic Rasio, the Joseph Cummings Professor   
   of Physics and Astronomy at Weinberg and member of CIERA.   
      
   While astrophysicists have proven the existence of lower- and higher-mass   
   block holes, intermediate-mass black holes have remained elusive. Created   
   when supernovae collapse, stellar remnant black holes are about 3   
   to 10 times the mass of our sun. On the other end of the spectrum,   
   supermassive black holes, which lurk in the centers of galaxies, are   
   millions to billions times the mass of our sun.   
      
   Should they exist, intermediate-mass black holes would fit somewhere in   
   the middle -- 10 to 10,000 times more massive than stellar remnant black   
   holes but not nearly as massive as supermassive black holes. Although   
   these intermediate- mass black holes theoretically should exist,   
   astrophysicists have yet to find indisputable observational evidence.   
      
   "Their presence is still debated," Kıroğlu   
   said. "Astrophysicists have uncovered evidence that they exist, but   
   that evidence can often be explained by other mechanisms. For example,   
   what appears to be an intermediate- mass black hole might actually be   
   the accumulation of stellar-mass black holes."  To explore the behavior   
   of these evasive objects, Kıroğlu and her team developed   
   new hydrodynamic simulations. First, they created a model of a star,   
   consisting of many particles. Then, they sent the star toward the black   
   hole and calculated the gravitational force acting on the particles   
   during the star's approach.   
      
   "We can calculate specifically which particle is bound to the star   
   and which particle is disrupted (or no longer bound to the star),"   
   Kıroğlu said.   
      
   Through these simulations, Kıroğlu and her team discovered   
   that stars could orbit an intermediate-mass black hole as many as five   
   times before finally being ejected. With each pass around the black hole,   
   the star loses more and more of its mass as its ripped apart. Then, the   
   black hole kicks the leftovers -- moving at searing speeds -- back out   
   into the galaxy. The repeating pattern would create a stunning light show   
   that should help astronomers recognize -- and prove the existence of --   
   intermediate-mass black holes.   
      
   "It's amazing that the star isn't fully ripped apart," Kıroğlu   
   said.   
      
   "Some stars might get lucky and survive the event. The ejection speed   
   is so high that these stars could be identified as hyper-velocity   
   stars, which have been observed at the centers of galaxies."  Next,   
   Kıroğlu plans to simulate different types of stars, including   
   giant stars and binary stars, to explore their interactions with black   
   holes.   
      
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Black_Holes # Stars # Galaxies # Astronomy #   
                   Astrophysics # Solar_Flare # Extrasolar_Planets #   
                   Northern_Lights   
       * RELATED_TERMS   
             o Red_supergiant_star o Supergiant o Gravitational_wave o Galaxy   
             o Geosynchronous_orbit o Globular_cluster o General_relativity   
             o Barred_spiral_galaxy   
      
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   Story Source: Materials provided by Northwestern_University. Note:   
   Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Fulya Kıroğlu, James C. Lombardi Jr., Kyle Kremer, Giacomo   
         Fragione, Shane Fogarty, Frederic A. Rasio. Tidal Disruption of   
         Main- Sequence Stars by Intermediate-Mass Black Holes. submitted   
         to arXiv, 2023 DOI: 10.48550/arXiv.2210.08002   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/04/230425205336.htm   
      
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