US, WASHINGTON (ORDO NEWS) — Black holes are not stationary objects in the Universe and can be quite active in their movements. But, since they do not emit and do not reflect light and cannot be observed directly, they are also not easy to study.
In the galaxy OJ 287 is one of the largest known black holes, the mass of which is 18 billion times greater than the solar one. There is a black hole in the orbit of this monster, whose mass is 120 times less.
Every 12 years, a smaller black hole makes a complete revolution around its neighbor, while twice crossing its huge accretion disk, resulting in powerful flashes of light – they are brighter than a trillion stars and the entire Milky Way.
But the orbit of the smaller black hole is oblong, not round, and it is irregular: it moves with each loop around the larger black hole and tilts relative to the accretion disk.
Due to an incorrect orbit, a black hole collides with the disk at different times during a 12-year cycle. Sometimes outbreaks appear after only a year; in other cases after 10 years.
Attempts to simulate the orbit and predict when outbreaks occurred took decades, but in 2010, scientists created a model that was able to predict their occurrence with an accuracy of one to three weeks. They demonstrated that their model was correct by predicting a flash in December 2015 with an accuracy of three weeks.
In 2018, a group of scientists led by Lankeswar Dey, a graduate student at the Tata Institute of Basic Research in Mumbai, published an article with an even more detailed model, which they claimed would be able to predict the time of future outbreaks with an accuracy of four hours.
In a new study published in the Astrophysical Journal Letters, these scientists report that their accurate prediction of an outbreak on July 31, 2019 confirms that the model is correct.
However, the researchers had difficulty directly observing this outbreak, since the OJ 287 galaxy was out of sight of all terrestrial telescopes and devices in Earth orbit, blocked by the Sun. The only one who was able to observe the outbreak was the Spitzer, which was decommissioned in January 2020.
After 16 years of operation, Spitzer was in orbit at a distance of 254 million kilometers from Earth, which is more than 600 times greater than the distance of the moon from our planet. The Spitzer could observe the system from July 31 (the same day that the outbreak was expected) until early September, when OJ 287 became visible to telescopes on Earth.
“When I first checked the visibility of OJ 287, I was shocked to find that it became visible to Spitzer the day that the next outbreak was predicted to happen. It’s extremely fortunate that we were able to capture the peak of this outbreak with Spitzer, because no other human-made devices could do this, ”said Seppo Lane, a researcher at the University of California.
Scientists regularly model the orbits of small objects in the solar system, such as comets orbiting our star. In this case, researchers take into account the factors that most strongly affect the movement of these objects. For comets, the dominant force is the gravity of the Sun, however, the gravitational attraction of the planets can also affect their path.
Determining the movement of two huge black holes is much more difficult. Scientists must consider factors that cannot significantly affect smaller objects; chief among them are the so-called gravitational waves. Einstein’s theory of general relativity describes gravity as a deformation of space by the mass of an object. When an object moves in space, distortions turn into waves. Einstein predicted the existence of gravitational waves in 1916, but they were not observed directly until 2015.
While previous studies of OJ 287 took gravity waves into account, the 2018 model has become even more detailed. To further refine the forecast of outbreaks up to four hours, scientists described in detail the physical characteristics of a larger black hole. In particular, the new model includes what is called the black hole hair loss theorem.
According to this theorem, the metric of a black hole is completely determined by only three of its parameters – mass, angular momentum (spin), and electric charge. All other information about the matter that the black hole absorbs is hidden behind the event horizon and is lost to the outside observer.
Published in the 1960s by a group of physicists, which included Stephen Hawking, this theorem predicts the nature of the “surfaces” of black holes. Although black holes do not have real surfaces, scientists know that there is a border around them, beyond which nothing – not even light – can escape. According to some versions, the outer edge, called the event horizon, may be uneven or irregular, but the absence of hair theorem states that the “surface” does not have such features, not even hair (the name of this theorem was a joke).
So how does the “smoothness” of the surface of a massive black hole affect the orbit of a smaller black hole? This orbit is determined mainly by the mass of a larger black hole. If it becomes more massive or vice versa loses some of its weight, this will change the orbit of a smaller black hole. But mass distribution also matters. A massive bulge on one side of a larger black hole would distort the space around it differently than if the black hole were symmetrical.
Since the researchers built their model for a smooth axisymmetric black hole, the correctness of the predictions speaks in favor of the absence of hair theorem.
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