MSGID: 1:317/3 6273534e   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Astronomers discover a rare 'black widow' binary, with the shortest   
   orbit yet    
    The system is orbited by third stellar companion and may have originated   
   near the center of the Milky Way.    
      
     Date:   
         May 4, 2022   
     Source:   
         Massachusetts Institute of Technology   
     Summary:   
         Astronomers discovered a 'black widow binary' -- a rapidly spinning   
         neutron star circling and slowly consuming a smaller companion star.   
      
         Named ZTF J1406+1222, the pair has the shortest orbital period yet   
         identified, and is unique in that it appears to host a third star   
         that orbits around the two inner stars every 10,000 years.   
      
      
      
   FULL STORY   
   ==========================================================================   
   The flashing of a nearby star has drawn MIT astronomers to a new and   
   mysterious system 3,000 light years from Earth. The stellar oddity appears   
   to be a new "black widow binary" -- a rapidly spinning neutron star, or   
   pulsar, that is circling and slowly consuming a smaller companion star,   
   as its arachnid namesake does to its mate.   
      
      
   ==========================================================================   
   Astronomers know of about two dozen black widow binaries in the Milky   
   Way. This newest candidate, named ZTF J1406+1222, has the shortest orbital   
   period yet identified, with the pulsar and companion star circling each   
   other every 62 minutes. The system is unique in that it appears to host   
   a third, far-flung star that orbits around the two inner stars every   
   10,000 years.   
      
   This likely triple black widow is raising questions about how such   
   a system could have formed. Based on its observations, the MIT team   
   proposes an origin story: As with most black widow binaries, the triple   
   system likely arose from a dense constellation of old stars known as a   
   globular cluster. This particular cluster may have drifted into the Milky   
   Way's center, where the gravity of the central black hole was enough to   
   pull the cluster apart while leaving the triple black widow intact.   
      
   "It's a complicated birth scenario," says Kevin Burdge, a Pappalardo   
   Postdoctoral Fellow in MIT's Department of Physics. "This system has   
   probably been floating around in the Milky Way for longer than the sun   
   has been around."  Burdge is the author of a study appearing in Nature   
   that details the team's discovery. The researchers used a new approach   
   to detect the triple system.   
      
   While most black widow binaries are found through the gamma and X-ray   
   radiation emitted by the central pulsar, the team used visible light,   
   and specifically the flashing from the binary's companion star, to detect   
   ZTF J1406+1222.   
      
   "This system is really unique as far as black widows go, because we found   
   it with visible light, and because of its wide companion, and the fact   
   it came from the galactic center," Burdge says. "There's still a lot we   
   don't understand about it. But we have a new way of looking for these   
   systems in the sky."  The study's co-authors are collaborators from   
   multiple institutions, including the University of Warwick, Caltech,   
   the University of Washington, McGill University, and the University   
   of Maryland.   
      
      
      
   ==========================================================================   
   Day and night Black widow binaries are powered by pulsars -- rapidly   
   spinning neutron stars that are the collapsed cores of massive   
   stars. Pulsars have a dizzying rotational period, spinning around every   
   few milliseconds, and emitting flashes of high-energy gamma and X-rays   
   in the process.   
      
   Normally, pulsars spin down and die quickly as they burn off a huge   
   amount of energy. But every so often, a passing star can give a pulsar new   
   life. As a star nears, the pulsar's gravity pulls material off the star,   
   which provides new energy to spin the pulsar back up. The "recycled"   
   pulsar then starts reradiating energy that further strips the star,   
   and eventually destroys it.   
      
   "These systems are called black widows because of how the pulsar sort of   
   consumes the thing that recycled it, just as the spider eats its mate,"   
   Burdge says.   
      
   Every black widow binary to date has been detected through gamma and   
   X-ray flashes from the pulsar. In a first, Burdge came upon ZTF J1406+1222   
   through the optical flashing of the companion star.   
      
      
      
   ==========================================================================   
   It turns out that the companion star's day side -- the side perpetually   
   facing the pulsar -- can be many times hotter than its night side,   
   due to the constant high-energy radiation it receives from the pulsar.   
      
   "I thought, instead of looking directly for the pulsar, try looking for   
   the star that it's cooking," Burdge explains.   
      
   He reasoned that if astronomers observed a star whose brightness was   
   changing periodically by a huge amount, it would be a strong signal that   
   it was in a binary with a pulsar.   
      
   Star motion To test this theory, Burdge and his colleagues looked through   
   optical data taken by the Zwicky Transient Facility, an observatory   
   based in California that takes wide-field images of the night sky. The   
   team studied the brightness of stars to see whether any were changing   
   dramatically by a factor of 10 or more, on a timescale of about an hour   
   or less -- signs that indicate the presence of a companion star orbiting   
   tightly around a pulsar.   
      
   The team was able to pick out the dozen known black widow binaries,   
   validating the new method's accuracy. They then spotted a star whose   
   brightness changed by a factor of 13, every 62 minutes, indicating   
   that it was likely part of a new black widow binary, which they labeled   
   ZTF J1406+1222.   
      
   They looked up the star in observations taken by Gaia, a space telescope   
   operated by the European Space Agency that keeps precise measurements   
   of the position and motion of stars in the sky. Looking back through   
   decades old measurements of the star? from the Sloan Digital Sky Survey,   
   the team found that the binary was being trailed by another distant   
   star. Judging from their calculations, this third star appeared to be   
   orbiting the inner binary every 10,000 years.   
      
   Curiously, the astronomers have not directly detected gamma or X-ray   
   emissions from the pulsar in the binary, which is the typical way in which   
   black widows are confirmed. ZTF J1406+1222, therefore, is considered   
   a candidate black widow binary, which the team hopes to confirm with   
   future observations.   
      
   "The one thing we know for sure is that we see a star with a day side   
   that's much hotter than the night side, orbiting around something every   
   62 minutes," Burdge says. "Everything seems to point to it being a black   
   widow binary. But there are a few weird things about it, so it's possible   
   it's something entirely new."  The team plans to continue observing the   
   new system, as well as apply the optical technique to illuminate more   
   neutron stars and black widows in the sky.   
      
   This research was supported, in part, by the National Science Foundation.   
      
      
   ==========================================================================   
   Story Source: Materials provided by   
   Massachusetts_Institute_of_Technology. Original written by Jennifer   
   Chu. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Related Multimedia:   
       * Black_widow_pulsar_and_its_stellar_companion   
   ==========================================================================   
   Journal Reference:   
      1. Kevin B. Burdge, Thomas R. Marsh, Jim Fuller, Eric C. Bellm, Ilaria   
         Caiazzo, Deepto Chakrabarty, Michael W. Coughlin, Kishalay De, V. S.   
      
         Dhillon, Matthew J. Graham, Pablo Rodri'guez-Gil, Amruta D. Jaodand,   
         David L. Kaplan, Erin Kara, Albert K. H. Kong, S. R. Kulkarni,   
         Kwan-Lok Li, S. P. Littlefair, Walid A. Majid, Przemek Mro'z, Aaron   
         B. Pearlman, E. S. Phinney, Jan van Roestel, Robert A. Simcoe,   
         Igor Andreoni, Andrew J. Drake, Richard G. Dekany, Dmitry A. Duev,   
         Erik C. Kool, Ashish A.   
      
         Mahabal, Michael S. Medford, Reed Riddle, Thomas A. Prince. A   
         62-minute orbital period black widow binary in a wide hierarchical   
         triple. Nature, 2022; 605 (7908): 41 DOI: 10.1038/s41586-022-04551-1   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2022/05/220504110446.htm   
      
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