Two black holes orbit each other but usually only see the jet of one of them A rare observation made it possible to see the other as well and provide new insights
In 2021, a NASA exoplanet-hunting satellite aimed at the galaxy OJ 287 to help astronomers verify the theory of two black holes at the center of the galaxy, first proposed by researchers at the University of Turku, Finland.
The Extrasolar Planet Survey Satellite (TESS) is designed to discover thousands of extrasolar planets orbiting the brightest dwarf stars in the sky. Tess finds planets across the spectrum from small rocky worlds to giants, showing the diversity of planets in our galaxy. He has so far found 410 confirmed extrasolar planets, or "new worlds," orbiting stars other than the Sun.
A NASA flight discovers extrasolar planets, worlds outside our solar system. During extensive sky observations, Tess also finds and tracks all kinds of objects whose brightness changes, from nearby asteroids to pulsating stars and distant galaxies that contain supernovae. Credit: NASA's Goddard Space Flight Center
In 2021, Tess spent several weeks studying a different type of system, a distant galaxy called OJ 287. Researchers found evidence of a very massive black hole in OJ 287 orbiting a supermassive dawn hole a hundred times larger.
To verify the existence of the smaller black hole, Tess tracked the brightness of the main black hole and its associated jet. The small black hole orbiting the larger one is difficult to observe directly, but a sudden burst of brightness revealed to researchers that it was present. This type of event has never been observed before in OJ 287, but researcher Pauli Piahayuki of the University of Turku, Finland predicted the event in his doctoral thesis back in 2014. According to the work, the next eruption was expected to occur in late 2021, and several satellites and telescopes were focused on the object at that time.
The Tess satellite detected the expected eruption on November 12, 2021 at 02:00 GMT, and the observations were recently published in a study. The event lasted only 12 hours. This short continuation shows that it is very difficult to find a burst of great brightness unless its timing is known in advance. In this case, the theory of the Turkish researchers was proven correct, and Tess targeted OJ 287 at exactly the right time. The discovery was also verified by NASA's Swift telescope, which also aimed at the same target.
In addition, a large international collaboration led by the Pole Staszek Zola discovered the same event by using telescopes in different parts of the world, so that there was always night in at least one place of the telescopes throughout the day. Furthermore, a group from Boston University verified the discovery by studying the polarization of light before and after the flare.
In a new study that combines all previous observations, Prof. 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.
The rapid burst of brightness occurs when the small black hole "swallows" a large piece of the accretion disk surrounding the large black hole, turning it into an outgoing jet of gas. So the jet of the small black hole is brighter than the jet of the large black hole for about 12 hours. As a result the color of OJ 287 becomes less red, or yellow, instead of the usual red. The yellow color indicates that in the 12 hours we see the light from the little black hole. The same result can be inferred from other properties of the light emitted from OJ 287 at the same time.
"Therefore, we can now say that we have "seen" an orbiting black hole 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 very difficult to get a direct image of the little black hole. In fact, because of the great distance of OJ 287, close to four billion light-years, it will probably be a long time before our observational methods develop enough to capture an image of even the big black hole," says Prof. Veltonen.
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Suggestion for correcting errors:
Third paragraph: "Indirect evidence of a very massive black hole in OJ287 orbiting a supermassive black hole" -> "Indirect evidence of a very massive black hole in OJ287 orbiting a supermassive black hole".
Fourth paragraph: "He revealed to the investigators that they discovered his presence" -> "He revealed to the investigators his presence".