At the cores of active galaxies, supermassive black holes can be found that
are several billion times more massive than our sun. They are seen by
astronomers as the luminous centers of galaxies where the supermassive black
hole of the galaxy eats material from a turbulent vortex known as the
accretion disk. A portion of the material is forced into a strong jet. The
galactic center now radiates intensely over the whole electromagnetic
spectrum as a result of this activity.
In a recent research, astronomers discovered signs from the jets connected
to the accretion of matter into both black holes that suggested the
existence of two supermassive black holes orbiting each other. The galaxy,
or quasar as it is officially known, is designated OJ287, and a binary black
hole system has received the greatest attention and is the subject of the
finest research. The black holes in the sky are so close to one another that
they combine as a single dot. By seeing that the dot produces two distinct
sorts of signals, it becomes clear that it actually comprises of two black
holes. The results have been published in the Royal Astronomical Society's
Monthly Notices.
Astronomers have been observing the active galaxy OJ 287 since 1888. It is
located in the direction of the constellation Cancer at a distance of around
5 billion light years. Aimo Sillanpää of the University of Turku and his
colleagues first observed a distinct pattern in the emission of this star
more than 40 years ago. This pattern has two cycles, the shorter of which
lasts for around 12 years and the longer for roughly 55 years. They proposed
that the two cycles are the consequence of two black holes orbiting one
another. The longer cycle occurs from a gradual development of the orbit's
orientation, whereas the shorter cycle is the orbital cycle.
A sequence of flares that appear as the secondary black hole repeatedly
plunges through the original black hole's accretion disk at speeds that are
only a little bit slower than the speed of light indicate the orbital
motion. The material in the disk is heated by the secondary black hole's
descent, and the heated gas is ejected as expanding bubbles. It takes months
for these hot bubbles to cool while they emit a flare that lasts nearly a
fortnight and is brighter than a trillion stars.
Astronomers from the University of Turku in Finland, led by Mauri Valtonen
and his collaborator Achamveedu Gopakumar from the Tata Institute of
Fundamental Research in Mumbai, India, and others, were able to model the
orbit and predict the exact timing of these flares after decades of work
estimating the secondary black hole's plunge through the accretion
disk.
The team was able to witness the expected flares and prove the existence of
a supermassive black hole pair in OJ 287 thanks to successful observational
missions in 1983, 1994, 1995, 2005, 2007, 2015, and 2019.
"As of right now, 26 anticipated flares have been detected, which is almost
the entire amount. According to Professor Achamveedu Gopakumar, the
companion black hole in this pair is around 100 times lighter and has an
orbit that is oblong rather than circular. The larger black hole in this duo
weighs more than 18 billion times the mass of the sun.
Astronomers had not been successful in directly seeing a signal from the
tiny black hole despite their best attempts. Prior until 2021, its existence
could only be inferred indirectly from the flares and the way it causes the
larger black hole's jet to bob.
The two black holes blend into a single point in our telescopes because
they are so near to one another in the sky. According to the primary author,
Professor Mauri Valtonen, "we can only claim to have genuinely "seen" both
black holes if we observe distinctly distinct signals from each one.
First direct observation of a smaller black hole
Excitingly, the observational campaigns on OJ 287 in 2021–2022, which made
use of numerous telescopes of various types, enabled scientists to observe
the secondary black hole for the first time as it descended through the
accretion disk as well as the signals emanating from the smaller black
hole.
"The years 2021 and 2022 were particularly important for the research of
OJ287. It was previously expected that the secondary black hole will eat
through its more massive companion's accretion disk during this time.
According to Professor Mauri Valtonen, "This plummeting was projected to
result in a strong blue flash immediately following the impact, and it was
in fact spotted, days before the estimated time, by Martin Jelinek and
associates at the Czech Technical University and Astronomical Institute of
Czechia.
There were two major shocks, though: brand-new flare varieties that had
never been seen before. Only Staszek Zola from the Jagiellonian University
in Cracow, Poland, conducted a thorough observation campaign to witness the
first of them, and with good cause. In just one day, Zola and his crew saw a
powerful flare that produced 100 times as much light as an entire
galaxy.
"According to the estimations, the flare happened soon after the smaller
black hole had taken in a significant amount of fresh gas during its dive.
The abrupt brightness of OJ287 is caused by the swallowing motion. It is
assumed that this process has strengthened the jet that emerges from the OJ
287's tiny black hole. A similar occurrence was anticipated 10 years ago,
but it wasn't proven until today, according to Valtonen.
Gamma rays produced the second unexpected signal, which NASA's Fermi
telescope saw. Just as the smaller black hole was about to pass through the
gas disk of the larger black hole, OJ287 had its largest gamma ray flare in
six years. Gamma rays are produced as a result of the interaction between
the disk gas and the smaller black hole's jet. To support this theory, the
researchers looked for evidence that a comparable gamma ray flare had
previously occurred in 2013, when the little black hole had previously
passed through the gas disk and been seen from the same vantage point.
"So why haven't we seen the one-day explosion before? What about it? Since
1888, OJ287 has been captured on camera, and since 1970, it has been closely
monitored. It turns out that we've just had lousy luck overall. On those
nights when OJ287 performed its one-night stunt, nobody specifically saw it.
We would have missed it again if Zola's squad hadn't been keeping a close
eye on things, according to Valtonen.
OJ 287 is now the top contender for a pair of supermassive black holes that
is emitting gravitational waves at nano-hertz frequencies as a result of
these studies. Additionally, OJ 287 is frequently observed by the Global
mm-VLBI Array (GMVA) and Event Horizon Telescope (EHT) consortia in an
effort to find more proof of the existence of a supermassive black hole pair
at the object's center and, in particular, to obtain a radio picture of the
secondary jet.
Provided by
University of Turku
