MSGID: 1:317/3 649e5a87   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Harnessing advanced simulation tools, a team of scientists from UNIGE,   
   Northwestern University and University of Florida shed light on the enigmatic   
   nature of these celestial 'beasts'.    
      
     Date:   
         June 29, 2023   
     Source:   
         Universite' de Gene`ve   
     Summary:   
         Black holes, some of the most captivating entities in the cosmos,   
         possess an immense gravitational pull so strong that not even   
         light can escape.   
      
         The groundbreaking detection of gravitational waves in 2015, caused   
         by the coalescence of two black holes, opened a new window into   
         the universe. Since then, dozens of such observations have sparked   
         the quest among astrophysicists to understand their astrophysical   
         origins. Thanks to the POSYDON code's recent major advancements in   
         simulating binary-star populations, a team of scientists predicted   
         the existence of merging massive, 30 solar mass black hole binaries   
         in Milky Way-like galaxies, challenging previous theories.   
      
      
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   FULL STORY   
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   Black holes, some of the most captivating entities in the cosmos,   
   possess an immense gravitational pull so strong that not even light   
   can escape. The groundbreaking detection of gravitational waves in 2015,   
   caused by the coalescence of two black holes, opened a new window into the   
   universe. Since then, dozens of such observations have sparked the quest   
   among astrophysicists to understand their astrophysical origins. Thanks   
   to the POSYDON code's recent major advancements in simulating binary-star   
   populations, a team of scientists, including some from the University   
   of Geneva (UNIGE), Northwestern University and the University of Florida   
   (UF) predicted the existence of merging massive, 30 solar mass black hole   
   binaries in Milky Way-like galaxies, challenging previous theories. These   
   results are published in Nature Astronomy.   
      
   Stellar-mass black holes are celestial objects born from the collapse of   
   stars with masses of a few to low hundreds of times that of our sun. Their   
   gravitational field is so intense that neither matter nor radiation can   
   evade them, making their detection exceedingly difficult. Therefore, when   
   the tiny ripples in spacetime produced by the merger of two black holes   
   were detected in 2015, by the Laser Interferometer Gravitational-wave   
   Observatory (LIGO), it was hailed as a watershed moment. According   
   to astrophysicists, the two merging black holes at the origin of the   
   signal were about 30 times the mass of the sun and located 1.5 billion   
   light-years away.   
      
   Bridging Theory and Observation What mechanisms produce these black   
   holes? Are they the product of the evolution of two stars, similar to our   
   sun but significantly more massive, evolving within a binary system? Or   
   do they result from black holes in densely populated star clusters   
   running into each other by chance? Or might a more exotic mechanism be   
   involved? All of these questions are still hotly debated today.   
      
   The POSYDON collaboration, a team of scientists from institutions   
   including the University of Geneva (UNIGE), Northwestern and the   
   University of Florida (UF) has made significant strides in simulating   
   binary-star populations. This work is helping to provide more accurate   
   answers and reconcile theoretical predictions with observational data. "As   
   it is impossible to directly observe the formation of merging binary   
   black holes, it is necessary to rely on simulations that reproduce their   
   observational properties. We do this by simulating the binary-star systems   
   from their birth to the formation of the binary black hole systems,"   
   explains Simone Bavera, a post-doctoral researcher at the Department   
   of Astronomy of the UNIGE's Faculty of Science and leading author of   
   this study.   
      
   Pushing the Limits of Simulation Interpreting the origins of merging   
   binary black holes, such as those observed in 2015, requires comparing   
   theoretical model predictions with actual observations. The technique used   
   to model these systems is known as "binary population synthesis." "This   
   technique simulates the evolution of tens of millions of binary star   
   systems in order to estimate the statistical properties of the resulting   
   gravitational-wave source population. However, to achieve this in a   
   reasonable time frame, researchers have until now relied on models that   
   use approximate methods to simulate the evolution of the stars and their   
   binary interactions. Hence, the oversimplification of single and binary   
   stellar physics leads to less accurate predictions," explains Anastasios   
   Fragkos, assistant professor in the Department of Astronomy at the UNIGE   
   Faculty of Science.   
      
   POSYDON has overcome these limitations. Designed as open-source software,   
   it leverages a pre-computed large library of detailed single- and   
   binary-star simulations to predict the evolution of isolated binary   
   systems. Each of these detailed simulations might take up to 100 CPU   
   hours to run on a supercomputer, making this simulation technique   
   not directly applicable for binary population synthesis. "However, by   
   precomputing a library of simulations that cover the entire parameter   
   space of initial conditions, POSYDON can utilize this extensive dataset   
   along with machine learning methods to predict the complete evolution   
   of binary systems in less than a second. This speed is comparable to   
   that of previous-generation rapid population synthesis codes, but with   
   improved accuracy," explains Jeffrey Andrews, assistant professor in   
   the Department of Physics at UF.   
      
   Introducing a New Model "Models prior to POSYDON predicted a negligible   
   formation rate of merging binary black holes in galaxies similar to the   
   Milky Way, and they particularly did not anticipate the existence of   
   merging black holes as massive as 30 times the mass of our sun. POSYDON   
   has demonstrated that such massive black holes might exist in Milky   
   Way-like galaxies," explains Vicky Kalogera, a Daniel I.   
      
   Linzer Distinguished University Professor of Physics and Astronomy in   
   the Department of Physics and Astronomy at Northwestern, director of   
   the Center of Interdisciplinary Exploration and Research in Astrophysics   
   (CIERA), and co- author of this study.   
      
   Previous models overestimated certain aspects, such as the expansion   
   of massive stars, which impacts their mass loss and the binary   
   interactions. These elements are key ingredients that determine the   
   properties of merging black holes. Thanks to fully self-consistent   
   detailed stellar-structure and binary- interaction simulations, POSYDON   
   achieves more accurate predictions of merging binary black hole properties   
   such as their masses and spins.   
      
   This study is the first to utilize the newly released open-source   
   POSYDON software to investigate merging binary black holes. It provides   
   new insights into the formation mechanisms of merging black holes in   
   galaxies like our own.   
      
   The research team is currently developing a new version of POSYDON, which   
   will include a larger library of detailed stellar and binary simulations,   
   capable of simulating binaries in a wider range of galaxy types.   
      
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Black_Holes # Stars # Astrophysics # Galaxies #   
                   Astronomy # Solar_Flare # Extrasolar_Planets # Sun   
       * RELATED_TERMS   
             o Black_hole o Gravitational_wave o Galaxy o General_relativity   
             o Holographic_Universe o Quasar o Dark_matter o   
             Spitzer_space_telescope   
      
   ==========================================================================   
   Story Source: Materials provided by Universite'_de_Gene`ve. Note:   
   Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Simone S. Bavera, Tassos Fragos, Emmanouil Zapartas, Jeff   
      J. Andrews,   
         Vicky Kalogera, Christopher P. L. Berry, Matthias Kruckow, Aaron   
         Dotter, Konstantinos Kovlakas, Devina Misra, Kyle A. Rocha,   
         Philipp M.   
      
         Srivastava, Meng Sun, Zepei Xing. The formation of merging   
         black holes with masses beyond 30 M⊙ at solar   
         metallicity. Nature Astronomy, 2023; DOI: 10.1038/s41550-023-02018-5   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230629125715.htm   
      
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