The Spitzer Space Telescope confirms that black holes are bald. No hair, not one

Black holes are really annoying objects. Although we know quite a lot about them, for example, we still do not know much about how they move in space. No wonder, after all, they are completely dark and can not be observed directly. Now, however, scientists have been able to accurately trace the movement, or even dance, of two huge black holes.

The galaxy OJ 287, a small 3.5 million light years away from us, is home to one of the largest black holes discovered so far. The mass of the monster inside OJ 287 is estimated at 18 million solar masses. As if that wasn't enough, around this really supermassive black hole revolves another, smaller with a mass of "only" 150 million solar masses. During the full lap, which takes 12 years, the smaller of the holes twice breaks through the vast gas disk surrounding the larger of them, causing a strong burst of radiation, stronger than the radiation of a billion (not a billion) stars, i.e. stronger than the glow of the entire Milky Way.

Oh, the supermassive black hole in the center of our galaxy has a mass of 4 million solar masses. So for the perspective that we don't feel so important.

Astronomers observing this system had one serious problem - a smaller black hole hits a larger gas disk irregularly. Sometimes a year passes between flares and sometimes it is ten years. This is due to the fact that the small black hole does not move in a circular orbit, but rather elongated, elliptical. As if that was not enough, the orbit is constantly changing its position relative to the central object. Hence, and attempts to predict when the next flare will take place were very difficult and would require decades of work.

Each time you hit the gas disk, a bubble of hot gas is formed that spreads in all directions. Less than 48 hours later, the brightness of the system increases four times.

Then, in 2010 ...

Astronomers create a model that seems to predict the appearance of another flare with an accuracy of three weeks. Considering that many years pass between successive collisions of the black hole with the disc, this is quite good accuracy. We had to wait until 2015 to confirm the model. To the satisfaction of astrophysicists, the black hole did not disappoint and fit into the three-week window provided five years earlier.

Three weeks is long, however. You can't go to the office, sit down and wait for confirmation of your forecast that "it is today at the other end of the universe that the black hole will ignite its surroundings again."

For this reason, in 2018, a group of scientists led by Lankeswar Dey, a PhD student from the Tata Institute of Fundamental Sciences in Mumbai, India, published an even more detailed model that, at least in theory, should enable meeting friends in the office and watching live flares in the galaxy 3.5 billion light years from Mumbai.

The new model enabled scientists to predict the next collision with an accuracy of four hours.

Needless to say, the flare that appeared on July 31, 2019, confirmed the correctness of the model.

We would hardly see anything.

After checking the predictions of the new model, researchers realized that they would not be able to see if the flare would actually occur, for one simple reason. On July 31, 2019, Galaxy OJ 287 was directly behind the Sun from our perspective, and no terrestrial instrument could observe it.

Spitzer enters the stage, all in white

Oh wait! The space telescope, which ended work in January 2020, six months earlier was the only one able to look towards the galaxy. Following the same orbit as Earth, the telescope was far enough behind it (254 million km) that it could calmly look behind the Sun and look at the galaxy of interest to us.

Spitzer began observations on July 31 and led them to the beginning of September, when the black hole had already "emerged" from behind the Sun and could be observed from Earth.

To the amazement of scientists, it turned out that the black hole became clear already on the first day of observation, which is exactly when Dey and his team predicted.

See how it looks like simulation!

Why, however, has such accuracy not been obtained before?

The answer is gravitational waves. Although theoretically predicted over 100 years ago by Albert Einstein, it was first observed in history only in 2015.

Sure, in previous studies, scientists took into account the fact that two black holes orbiting around each other emit gravitational waves, but they didn't know exactly what and how it affects the system.

Information from LIGO detectors, which in 2015 was the first to register gravitational waves, allowed to significantly detail the impact of gravitational waves on black holes rotating around them.

It turned out that the gravitational waves emitted by the system of two such massive black holes are so strong that they extract enough energy from the system to lead to constant changes in the orbit of the smaller black hole around the larger one.

Information from LIGO allowed to narrow the forecasts for the next collision with the disk to 36 hours.

Still not much, more would be wanted.

By refining their model, scientists came up with the idea to include in it details about the physical characteristics of a larger black hole, and more specifically to embed in the model the theory that "black holes have no hair".

The theory created in the sixties focuses on the "surfaces" of black holes. Of course, bright, black holes have no surface, but there is such a border, beyond which nothing can get out of it, not even light. Part of the theory was that such an outer edge of a black hole - the event horizon - can be uneven, irregular. The bald black hole theory states, however, that the black hole has absolutely no unevenness and the black holes as such are symmetrical about their axis of rotation.

The correct prediction of the moment of collision of a black hole with the gas disk of another black hole in its entirety confirms this theory. if on one side of the black hole there was a bulge, however small, it would change the orbit of the smaller black hole significantly and we would not be able to predict when the collision would occur.

For black hole scientists, confirming or denying the theory of black hole hair is extremely important. Without this we could not believe that the black holes predicted by Hawking and others exist at all, '' concludes astrophysicist Mauri Valtonen from the University of Turku in Finland.



The Spitzer Space Telescope confirms that black holes are bald. No hair, not one

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