MSGID: 1:317/3 6279ea82   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    In a pair of merging supermassive black holes, a new method for   
   measuring the void    
      
     Date:   
         May 9, 2022   
     Source:   
         Columbia University   
     Summary:   
         Researchers have devised a potentially easier way of gazing into   
         the abyss. Their imaging technique could allow astronomers to   
         study black holes smaller than M87's, a monster with a mass of   
         6.5 billion suns, harbored in galaxies more distant than M87,   
         which at 55 million light- years away, is still relatively close   
         to our own Milky Way.   
      
      
      
   FULL STORY   
   ==========================================================================   
   Three years ago, the first ever image of a black hole stunned the world. A   
   black pit of nothingness enclosed by a fiery ring of light. That iconic   
   image of the black hole at the center of galaxy Messier 87 came into focus   
   thanks to the Event Horizon Telescope, a global network of synchronized   
   radio dishes acting as one giant telescope.   
      
      
   ==========================================================================   
   Now, a pair of Columbia researchers have devised a potentially easier way   
   of gazing into the abyss. Outlined in complementary studies in Physical   
   Review Lettersand Physical Review D, their imaging technique could allow   
   astronomers to study black holes smaller than M87's, a monster with a   
   mass of 6.5 billion suns, harbored in galaxies more distant than M87,   
   which at 55 million light- years away, is still relatively close to our   
   own Milky Way.   
      
   The technique has just two requirements. First, you need a pair of   
   supermassive black holes in the throes of merging. Second, you need to   
   be looking at the pair at a nearly side-on angle. From this sideways   
   vantage point, as one black hole passes in front of the other, you   
   should be able to see a bright flash of light as the glowing ring of the   
   black hole farther away is magnified by the black hole closest to you,   
   a phenomenon known as gravitational lensing.   
      
   The lensing effect is well known, but what the researchers discovered   
   here was a hidden signal: a distinctive dip in brightness corresponding   
   to the "shadow" of the black hole in back. This subtle dimming can last   
   from a few hours to a few days, depending on how massive the black holes,   
   and how closely entwined their orbits. If you measure how long the dip   
   lasts, the researchers say, you can estimate the size and shape of the   
   shadow cast by the black hole's event horizon, the point of no exit,   
   where nothing escapes, not even light.   
      
   "It took years and a massive effort by dozens of scientists to make   
   that high- resolution image of the M87 black holes," said the study's   
   first author, Jordy Davelaar, a postdoc at Columbia and the Flatiron   
   Institute's Center for Computational Astrophysics. "That approach only   
   works for the biggest and closest black holes -- the pair at the heart of   
   M87 and potentially our own Milky Way."  He added, "with our technique,   
   you measure the brightness of the black holes over time, you don't need   
   to resolve each object spatially. It should be possible to find this   
   signal in many galaxies."  The shadow of a black hole is both its most   
   mysterious and informative feature.   
      
   "That dark spot tells us about the size of the black hole, the shape   
   of the space-time around it, and how matter falls into the black hole   
   near its horizon," said co-author Zoltan Haiman, a physics professor   
   at Columbia.   
      
      
      
   ==========================================================================   
   Black hole shadows may also hold the secret to the true nature of   
   gravity, one of the fundamental forces of our universe. Einstein's theory   
   of gravity, known as general relativity, predicts the size of black   
   holes. Physicists, therefore, have sought them out to test alternative   
   theories of gravity in an effort to reconcile two competing ideas of   
   how nature works: Einstein's general relativity, which explains large   
   scale phenomena like orbiting planets and the expanding universe, and   
   quantum physics, which explains how tiny particles like electrons and   
   photons can occupy multiple states at once.   
      
   The researchers became interested in flaring supermassive black holes   
   after spotting a suspected pair of supermassive black holes at the   
   center of a far- off galaxy in the early universe. NASA's planet-hunting   
   Kepler space telescope was scanning for the tiny dips in brightness   
   corresponding to a planet passing in front of its host star. Instead,   
   Kepler ended up detecting the flares of what Haiman and his colleagues   
   claim are a pair of merging black holes.   
      
   They named the distant galaxy "Spikey" for the spikes in brightness   
   triggered by its suspected black holes magnifying each other on each   
   full rotation via the lensing effect. To learn more about the flare,   
   Haiman built a model with his postdoc, Davelaar.   
      
   They were confused, however, when their simulated pair of black holes   
   produced an unexpected, but periodic, dip in brightness each time one   
   orbited in front of the other. At first, they thought it was a coding   
   mistake. But further checking led them to trust the signal.   
      
   As they looked for a physical mechanism to explain it, they realized   
   that each dip in brightness closely matched the time it took for the   
   black hole closest to the viewer to pass in front of the shadow of the   
   black hole in back.   
      
   The researchers are currently looking for other telescope data to try   
   and confirm the dip they saw in the Kepler data to verify that Spikey is,   
   in fact, harboring a pair of merging black holes. If it all checks out,   
   the technique could be applied to a handful of other suspected pairs   
   of merging supermassive black holes among the 150 or so that have been   
   spotted so far and are awaiting confirmation.   
      
   As more powerful telescopes come online in the coming years, other   
   opportunities may arise. The Vera Rubin Observatory, set to open this   
   year, has its sights on more than 100 million supermassive black   
   holes. Further black hole scouting will be possible when NASA's   
   gravitational wave detector, LISA, is launched into space in 2030.   
      
   "Even if only a tiny fraction of these black hole binaries has the right   
   conditions to measure our proposed effect, we could find many of these   
   black hole dips," Davelaar said.   
      
      
   ==========================================================================   
   Story Source: Materials provided by Columbia_University. Original written   
   by Kim Martineau.   
      
   Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Related Multimedia:   
       * Shadow_of_a_black_hole   
   ==========================================================================   
   Journal References:   
      1. Jordy Davelaar, Zolta'n Haiman. Self-Lensing Flares from Black Hole   
         Binaries: Observing Black Hole Shadows via Light Curve Tomography.   
      
         Physical Review Letters, 2022; 128 (19) DOI: 10.1103/   
         PhysRevLett.128.191101   
      2. Jordy Davelaar, Zolta'n Haiman. Self-lensing flares from black hole   
         binaries: General-relativistic ray tracing of black hole binaries.   
      
         Physical Review D, 2022; 105 (10) DOI: 10.1103/PhysRevD.105.103010   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2022/05/220509132625.htm   
      
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