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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