MSGID: 1:317/3 6270b052   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Search reveals eight new sources of black hole echoes    
      
     Date:   
         May 2, 2022   
     Source:   
         Massachusetts Institute of Technology   
     Summary:   
         Astronomers discovered eight new echoing black hole binaries in   
         our galaxy, enabling them to piece together a general picture of   
         how a black hole evolves during an outburst. The findings will   
         help scientists trace a black hole's evolution as it feeds on   
         stellar material.   
      
      
      
   FULL STORY   
   ==========================================================================   
   Scattered across our Milky Way galaxy are tens of millions of black   
   holes - - immensely strong gravitational wells of spacetime, from which   
   infalling matter, and even light, can never escape. Black holes are   
   dark by definition, except on the rare occasions when they feed. As a   
   black hole pulls in gas and dust from an orbiting star, it can give off   
   spectacular bursts of X-ray light that bounce and echo off the inspiraling   
   gas, briefly illuminating a black hole's extreme surroundings.   
      
      
   ==========================================================================   
   Now MIT astronomers are looking for flashes and echoes from nearby black   
   hole X-ray binaries -- systems with a star orbiting, and occasionally   
   being eaten away by, a black hole. They are analyzing the echoes from   
   such systems to reconstruct a black hole's immediate, extreme vicinity.   
      
   In a study appearing today in the Astrophysical Journal, the researchers   
   report using a new automated search tool, which they've coined the   
   "Reverberation Machine," to comb through satellite data for signs   
   of black hole echoes. In their search, they have discovered eight new   
   echoing black hole binaries in our galaxy. Previously, only two such   
   systems in the Milky Way were known to emit X-ray echoes.   
      
   In comparing the echoes across systems, the team has pieced together a   
   general picture of how a black hole evolves during an outburst. Across   
   all systems, they observed that a black hole first undergoes a "hard"   
   state, whipping up a corona of high-energy photons along with a jet of   
   relativistic particles that is launched away at close to the speed of   
   light. The researchers discovered that at a certain point, the black   
   hole gives off one final, high-energy flash, before transitioning to a   
   "soft," low-energy state.   
      
   This final flash may be a sign that a black hole's corona, the region of   
   high- energy plasma just outside a black hole's boundary, briefly expands,   
   ejecting a final burst of high-energy particles before disappearing   
   entirely. These findings could help to explain how larger, supermassive   
   black holes at the center of a galaxy can eject particles across vastly   
   cosmic scales to shape a galaxy's formation.   
      
   "The role of black holes in galaxy evolution is an outstanding question   
   in modern astrophysics," says Erin Kara, assistant professor of physics   
   at MIT.   
      
   "Interestingly, these black hole binaries appear to be 'mini' supermassive   
   black holes, and so by understanding the outbursts in these small, nearby   
   systems, we can understand how similar outbursts in supermassive black   
   holes affect the galaxies in which they reside."  The study's first   
   author is MIT graduate student Jingyi Wang; other co-authors include   
   Matteo Lucchini and Ron Remillard at MIT, along with collaborators from   
   Caltech and other institutions.   
      
      
      
   ==========================================================================   
   X-ray delays Kara and her colleagues are using X-ray echoes to map a   
   black hole's vicinity, much the way that bats use sound echoes to navigate   
   their surroundings. When a bat emits a call, the sound can bounce off an   
   obstacle and return to the bat as an echo. The time it takes for the echo   
   to return is relative to the distance between the bat and the obstacle,   
   giving the animal a mental map of its surroundings.   
      
   In similar fashion, the MIT team is looking to map the immediate   
   vicinity of a black hole using X-ray echoes. The echoes represent time   
   delays between two types of X-ray light: light emitted directly from   
   the corona, and light from the corona that bounces off the accretion   
   disk of inspiraling gas and dust.   
      
   The time when a telescope receives light from the corona, compared to when   
   it receives the X-ray echoes, gives an estimate of the distance between   
   the corona and the accretion disk. Watching how these time delays change   
   can reveal how a black hole's corona and disk evolve as the black hole   
   consumes stellar material.   
      
   Echo evolution In their new study, the team developed search algorithm   
   to comb through data taken by NASA's Neutron star Interior Composition   
   Explorer, or NICER, a high- time-resolution X-ray telescope aboard the   
   International Space Station. The algorithm picked out 26 black hole X-ray   
   binary systems that were previously known to emit X-ray outbursts. Of   
   these 26, the team found that 10 systems were close and bright enough   
   that they could discern X-ray echoes amid the outbursts. Eight of the   
   10 were previously not known to emit echoes.   
      
      
      
   ==========================================================================   
   "We see new signatures of reverberation in eight sources," Wang says. "The   
   black holes range in mass from five to 15 times the mass of the sun,   
   and they're all in binary systems with normal, low-mass, sun-like stars."   
   As a side project, Kara is working with MIT education and music scholars,   
   Kyle Keane and Ian Condry, to convert the emission from a typical X-ray   
   echo into audible sound waves.   
      
   Video Echos of a Black Hole: https://youtu.be/iIeIag2Ji8k The researchers   
   then ran the algorithm on the 10 black hole binaries and divided the   
   data into groups with similar "spectral timing features," that is,   
   similar delays between high-energy X-rays and reprocessed echoes. This   
   helped to quickly track the change in X-ray echoes at every stage during   
   a black hole's outburst.   
      
   The team identified a common evolution across all systems. In the initial   
   "hard" state, in which a corona and jet of high-energy particles dominates   
   the black hole's energy, they detected time lags that were short and   
   fast, on the order of milliseconds. This hard state lasts for several   
   weeks. Then, a transition occurs over several days, in which the corona   
   and jet sputter and die out, and a soft state takes over, dominated by   
   lower-energy X-rays from the black hole's accretion disk.   
      
   During this hard-to-soft transition state, the team discovered that time   
   lags grew momentarily longer in all 10 systems, implying the distance   
   between the corona and disk also grew larger. One explanation is that   
   the corona may briefly expand outward and upward, in a last high-energy   
   burst before the black hole finishes the bulk of its stellar meal and   
   goes quiet.   
      
   "We're at the beginnings of being able to use these light echoes to   
   reconstruct the environments closest to the black hole," Kara says. "Now   
   we've shown these echoes are commonly observed, and we're able to probe   
   connections between a black hole's disk, jet, and corona in a new way."   
   This research was supported, in part, by NASA.   
      
      
   ==========================================================================   
   Story Source: Materials provided by   
   Massachusetts_Institute_of_Technology. Original written by Jennifer   
   Chu. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Jingyi Wang, Erin Kara, Matteo Lucchini, Adam Ingram, Michiel   
      van der   
         Klis, Guglielmo Mastroserio, Javier A. Garci'a, Thomas Dauser,   
         Riley Connors, Andrew C. Fabian, James F. Steiner, Ron A. Remillard,   
         Edward M.   
      
         Cackett, Phil Uttley, Diego Altamirano. The NICER "Reverberation   
         Machine": A Systematic Study of Time Lags in Black Hole X-Ray   
         Binaries.   
      
         The Astrophysical Journal, 2022; 930 (1): 18 DOI: 10.3847/1538-4357/   
         ac6262   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2022/05/220502120519.htm   
      
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