MSGID: 1:317/3 648007f1   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    First detection of secondary supermassive black hole in a well-known   
   binary system    
      
     Date:   
         June 6, 2023   
     Source:   
         University of Turku   
     Summary:   
         An international team of astronomers observed the second one of   
         the two supermassive black holes circling each other in an active   
         galaxy OJ 287.   
      
      
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   FULL STORY   
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   Supermassive black holes that weigh several billion times the mass of our   
   Sun are present at the centres of active galaxies. Astronomers observe   
   them as bright galactic cores where the galaxy's supermassive black hole   
   devours matter from a violent whirlpool called accretion disk. Some of   
   the matter is squeezed out into a powerful jet. This process makes the   
   galactic core shine brightly across the entire electromagnetic spectrum.   
      
   In a recent study, astronomers found evidence of two supermassive   
   black holes circling each other through signals coming from the jets   
   associated with the accretion of matter into both black holes. The galaxy,   
   or a quasar as it is technically called, is named OJ287 and it is most   
   thoroughly studied and best understood as a binary black hole system. In   
   the sky, the black holes are so close together that they merge into one   
   dot. The fact that the dot actually consists of two black holes becomes   
   apparent by detecting that it emits two different types of signals.   
      
   The active galaxy OJ 287 lies in the direction of the constellation Cancer   
   at a distance of about 5 billion light years and has been observed by   
   astronomers since 1888. Already more than 40 years ago, astronomer from   
   University of Turku Aimo Sillanpa"a" and his associates noticed that   
   there is a prominent pattern in its emission which has two cycles, one   
   of about 12 years and the longer of about 55 years. They suggested that   
   the two cycles result from the orbital motion of two black holes around   
   each other. The shorter cycle is the orbital cycle and the longer one   
   results from a slow evolution of the orientation of the orbit.   
      
   The orbital motion is revealed by a series of flares which arise when the   
   secondary black hole plunges regularly through the accretion disk of the   
   primary black hole at speeds that are a fraction slower than the speed of   
   light. This plunging of the secondary black hole heats the disk material   
   and the hot gas is released as expanding bubbles. These hot bubbles take   
   months to cool while they radiate and cause a flash of light -- a flare --   
   that lasts roughly a fortnight and is brighter than a trillion stars.   
      
   After decades of efforts at estimating the timing of the secondary black   
   hole's plunge through the accretion disk, astronomers from the University   
   of Turku in Finland led by Mauri Valtonen and his collaborator Achamveedu   
   Gopakumar from the Tata Institute of Fundamental Research at Mumbai,   
   India, and others were able to model the orbit and to predict accurately   
   when these flares would occur.   
      
   Successful observational campaigns in 1983, 1994, 1995, 2005, 2007,   
   2015 and 2019 allowed the team to observe the predicted flares and to   
   confirm the presence of a supermassive black hole pair in OJ 287.   
      
   "The total number of predicted flares now number 26, and nearly all   
   of them have been observed. The bigger black hole in this pair weighs   
   more than 18 billion times the mass of our Sun while the companion is   
   roughly 100 times lighter and their orbit is oblong, not circular,"   
   Professor Achamveedu Gopakumar says.   
      
   In spite of these efforts, astronomers had not been able to observe a   
   direct signal from the smaller black hole. Before 2021, its existence   
   had been deduced only indirectly from the flares and from the way it   
   makes the jet of the bigger black hole wobble.   
      
   "The two black holes are so close to each other in the sky that one cannot   
   see them separately, they merge to a single point in our telescopes. Only   
   if we see clearly separate signals from each black hole can we say that   
   we have actually "seen" them both," says the lead author, Professor   
   Mauri Valtonen.   
      
   Smaller black hole directly observed for the first time Excitingly, the   
   observational campaigns in 2021/2022 on OJ 287 using a large number of   
   telescopes of various types allowed researchers to obtain observations   
   of the secondary black hole plunging through the accretion disk for the   
   first time, and the signals arising from the smaller black hole itself.   
      
   "The period in 2021/2022 had a special significance in the study of OJ287.   
      
   Earlier, it had been predicted that during this period the secondary   
   black hole will plunge through the accretion disk of its more massive   
   companion. This plunging was expected to produce a very blue flash right   
   after the impact, and it was indeed observed, within days of the predicted   
   time, by Martin Jelinek and associates at the Czech Technical University   
   and Astronomical Institute of Czechia," says Professor Mauri Valtonen.   
      
   However, there were two big surprises -- new types of flares which had   
   not been detected before. The first of them was seen only by a detailed   
   observation campaign by Staszek Zola from the Jagiellonian University   
   of Cracow, Poland, and for a good reason. Zola and his team observed a   
   big flare, producing 100 times more light than an entire galaxy, and it   
   lasted only one day.   
      
   "According to the estimates, the flare occurred shortly after the smaller   
   black hole had received a massive dose of new gas to swallow during its   
   plunge. It is the swallowing process that leads to the sudden brightening   
   of OJ287. It is thought that this process has empowered the jet which   
   shoots out from the smaller black hole of OJ 287. An event like this   
   was predicted ten years ago, but has not been confirmed until now,"   
   Valtonen explains.   
      
   The second unexpected signal came from gamma rays and it was observed by   
   NASA's Fermi telescope. The biggest gamma ray flare in OJ287 for six years   
   happened just when the smaller black hole plunged through the gas disk   
   of the primary black hole. The jet of the smaller black hole interacts   
   with the disk gas, and this interaction leads to the production of gamma   
   rays. To confirm this idea, the researchers verified that a similar gamma   
   ray flare had already taken place in 2013 when the small black hole fell   
   through the gas disk last time, seen from the same viewing direction.   
      
   "So what about the one-day burst, why have we not seen it before? OJ287   
   has been recorded in photographs since 1888 and has been intensively   
   followed since 1970. It turns out that we have simply just had bad   
   luck. Nobody observed OJ287 exactly on those nights when it did its   
   one-night stunt. And without the intense monitoring by Zola's group,   
   we would have missed it this time as well," Valtonen states.   
      
   These efforts make OJ 287 the best candidate for a supermassive   
   black hole pair that is sending gravitational waves in nano-hertz   
   frequencies. Further, OJ 287 is being routinely monitored by both   
   the Event Horizon Telescope (EHT) and the Global mm-VLBI Array   
   (GMVA) consortia to probe for additional evidence for the presence of   
   supermassive black hole pair at its centre and, in particular, to try   
   to get the radio image of the secondary jet.   
      
   The instruments that were part of the 2021-2022 campaign include NASA's   
   Fermi gamma ray telescope and the Swift ultraviolet to x-ray telescope,   
   optical wavelength observations by astronomers in Czech Republic,   
   Finland, Germany, Spain, Italy, Japan, India, China, Great Britain and   
   USA, and radio frequency observations of OJ287 at Aalto University,   
   Helsinki, Finland.   
      
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Black_Holes # Galaxies # Astronomy # Astrophysics #   
                   Stars # Solar_Flare # Space_Telescopes # Cosmic_Rays   
       * RELATED_TERMS   
             o Spitzer_space_telescope o Galaxy o Quasar o   
             Barred_spiral_galaxy o Interstellar_medium o Andromeda_Galaxy   
             o Galaxy_formation_and_evolution o Globular_cluster   
      
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   Story Source: Materials provided by University_of_Turku. Note: Content   
   may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Mauri J Valtonen, Staszek Zola, A Gopakumar, Anne La"hteenma"ki,   
      Merja   
         Tornikoski, Lankeswar Dey, Alok C Gupta, Tapio Pursimo, Emil   
         Knudstrup, Jose L Gomez, Rene Hudec, Martin Jeli'nek, Jan Strobl,   
         Andrei V Berdyugin, Stefano Ciprini, Daniel E Reichart, Vladimir   
         V Kouprianov, Katsura Matsumoto, Marek Drozdz, Markus Mugrauer,   
         Alberto Sadun, Michal Zejmo, Aimo Sillanpa"a", Harry J Lehto,   
         Kari Nilsson, Ryo Imazawa, Makoto Uemura. Refining the OJ 287   
         2022 impact flare arrival epoch. Monthly Notices of the Royal   
         Astronomical Society, 2023; 521 (4): 6143 DOI: 10.1093/mnras/stad922   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230606111711.htm   
      
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