Several international research groups have confirmed the theory that there is a black hole orbiting a larger one in the galaxy OJ 287, 3.5 billion light years away.
In 2021, NASA’s TESS exoplanet hunter targeted this galaxy to help astronomers confirm the theory initially proposed by researchers at the University of Turku, Finland, of two black holes at the center of the galaxy. The researchers found indirect evidence that a very massive black hole in OJ 287 is orbiting a giant black hole 100 times its size.
To verify the existence of the smaller black hole, TESS monitored the brightness of the primary black hole and the jet associated with it. Direct observation of the smaller black hole orbiting the larger one is very difficult, but its presence was revealed to researchers by a sudden burst of brightness.
The TESS satellite detected the predicted flare on November 12, 2021 at 0200 UTC, and the observations were recently published in a study in The Astrophysical Journal by Shubham Kishore, Alok Gupta (Aryabhatta Research Institute of Observational Sciences, India) and Paul Wiita (The College of New Jersey, USA).
The event lasted only 12 hours. This short duration shows that it is very difficult to find a burst of great brightness unless you know its timing in advance. In this case, the Turku researchers’ theory turned out to be correct and TESS was directed to OJ 287 at just the right time. The discovery was also confirmed by NASA’s Swift telescope, which was also pointed at the same target.
Furthermore, a large international collaboration led by Staszek Zola of the Jagiellonian University in Krakow, Poland, detected the same event using telescopes in different parts of the Earth, such that it was always night at least at one of the telescope locations during all day. Additionally, a group at Boston University led by Svetlana Jorstad and other observers confirmed the discovery by studying the polarization of light before and after the flare.
In a new study combining all previous observations, Professor Mauri Valtonen and his research team at the University of Turku have shown that the 12-hour burst of light came from the smaller orbiting black hole and its surroundings. This study was published in The Astrophysical Journal Letters.
The rapid burst of brightness occurs when the smaller black hole “swallows” a large portion of the accretion disk surrounding the larger black hole, turning it into an outward jet of gas.
The jet from the smaller black hole is then brighter than that from the larger black hole for about 12 hours. This makes the color of OJ287 less reddish, or yellow, instead of the normal red. After the explosion, the red color returns. The yellow color indicates that during the 12-hour period, we are seeing light from the smaller black hole. The same results can be inferred from other characteristics of the light emitted by OJ287 during the same time period.
“Therefore, we can now say that we have ‘seen’ a black hole in orbit for the first time, in the same way that we can say that TESS has seen planets orbiting other stars. And as with planets, it is extremely difficult to obtain a direct image of the smaller black hole. In fact, due to the great distance of OJ 287, which is close to four billion light years, it will probably be a long time before our observation methods have developed as much as possible. enough to capture an image of even the largest black hole,” Professor Valtonen says in a statement.
“However, the smaller black hole may soon reveal its existence in other ways, as it is expected to emit nano-Hertz gravitational waves. OJ 287’s gravitational waves should be detectable in the coming years by timing arrays from maturing pulsars,” says A. Gopakumar of the Tata Institute of Fundamental Research in India.
