Supermassive black holes — objects that are in the hundreds of millions or even billions of times more massive than normal stars, are perhaps the most mysterious objects in modern astrophysics. They are hiding in the hearts of most large galaxies, including our milky Way. Given their ubiquity, these black holes can play a vital role in the formation and evolution of the Universe. But how did they become so massive — this question is still bothering theorists all over the world.
The most reasonable speculation is that these monsters were able to grow so much, just absorbing the vast quantities of gas over billions of years — today refuted. Recent observations have shown the existence of black holes, which was billions of times more massive than the Sun already 800 million years after the Big Bang. And again, how they put on weight so quickly? The majority of astrophysicists agree that supermassive black holes were supposed to hatch from a small “seed” black holes. Just not clear how modest must be a seed. One school of thought believes that seed black holes must be large — thousands or tens of thousands of solar masses; the other, that the seeds may be small — no more than a hundred solar masses.
Both camps must do something to curb the fact that black holes are voracious eaters. Gravity can pull gas straight to the point, yet around the black hole will begin to accumulate substance, forming a white hot drive that emits intense radiation and repulsive incoming gas, thus cutting the supply of food. This is called the Eddington limit. It is believed that it seriously reduces the speed at which a black hole can absorb matter and grow. The advantage of models using small seeds that are polusrednem black holes are easy enough to manufacture; the disadvantage is that for a quick transformation into supermassive black holes, they have to bypass the Eddington limit, relying on various possible exceptions to circumvent its limitations. Models with a large seed, on the contrary, observe the limit, providing supermassive black holes a head start, so they can eat as much gas as possible before they reach the limit — but larger seeds are more difficult to do. A giant cloud of gas, which may collapse with the formation of large seeds may also break up into small pieces, forming a cluster of stars, not the big black holes.
Regardless of whether you are large or small seeds “had a lot of theories that try to explain the existence or the Assembly of supermassive black holes, but none of them offered a natural solution,” says Naoki Yoshida, an astrophysicist at the University of Tokyo. Yoshida is a supporter of big seeds and a co-author of an article published last week in the journal Science. In it, he told us how supermassive black holes formed unexpectedly large population of these in the young Universe. His “natural decision” involves high-speed streams of gas flowing through the Universe after the Big Bang and acting as an important catalyst. In particular, it relies on the expected interaction between the Hamiltonian and the dark matter — a mysterious invisible substance that apparently acts as gravitational glue of the galaxies.
Growing a black hole
Together with colleagues at the University of Texas at Austin and the University of tübingen in Germany Yoshida used a computer simulation to recreate conditions in the early Universe, setting the cosmological parameters, like the density of dark matter that astronomers have calculated, by measuring the composition of the early Universe.
“We tried to reproduce the original as close as possible to real observations,” says Yoshida, “and gave the Universe time to development”.
According to the simulations, the scientists, in some parts of the Universe gravity of dark matter can capture fast-moving streams of primary hydrogen and helium left after the Big Bang. Later, as scientists have found, these first gases were dispersed in some areas up to wild speeds — it became “fast wind,” says Yoshida. “You have to imagine how difficult it is to catch the gas that is moving too quickly,” says Yoshida. Put your hand under fire hose and the water will instantly win her. “The only way to stop this strong wind, you apply a strong enough gravity,” he says. Scientists estimate that for every three billion light-years away in the early Universe there was enough dark matter that its gravity could capture that wind if to send the river in reverse. This attraction between the gas and dark matter have created a large gas cloud and did not give to form small stars on the way.
The simulated gas cloud then collapsed in a massive star, which continued to absorb more gas until it reached 34 000 solar masses. This extraordinarily hypothetical massive star could reach such a value only in the case if it consisted of pure hydrogen and helium — the two elementary gases, which are circled in the early Universe before the first stars became supernovas, of which later came the heavy elements — carbon, nitrogen, oxygen. Similar ideas were voiced earlier, but a working model was presented for the first time.
“Our computer modeling has shown that such phenomena do occur, and such large stars can form,” says Yoshida. Typing a giant mass, the star finally collapses and becomes the seed for a supermassive black hole. Yoshida believes the decision is final and natural. But not everyone agree with him.
Good answer, but…
Other scientists who quite approve of the hypothesis with large seeds, otherwise see the initial formation of these seeds. A recently published study in Nature Astronomy, for example, suggests that such seeds are not formed in the process of the strange movements of dark matter, but rather due to the behavior of ordinary stars in galaxies. Under this scenario, powerful bursts of ultraviolet light in the process of rapid star formation in young galaxy near will not interfere with the formation of stars in giant gas cloud so that it will remain empty long enough to eventually collapse into a black hole with a mass of up to 100,000 solar.
John Weiss, astrophysicist Georgia Institute of Technology and research associate in Astronomy Nature, believes that this new work will be an important step forward in this area, because Yoshida and his colleagues first modeled the effects of movements of the first gas for the formation of supermassive black holes. But he says that their theory does not deny his own.
“I think there are many ways to form a supermassive black hole,” he says. “This is just one of them, it is possible”. However, he adds that to find such a fast-moving gases in the early Universe would be hard. The chances of stumbling on such winds in the early Universe, according to Yoshida, are of the order of 0.3%. But a giant gas cloud adjacent to the young factories of stars, will be a rarity, the scientist believes. “I don’t know, what is the probability of this event,” says Yoshida.
Greg Bryan, Columbia University astrophysicist and the lead author of the work in Astronomy Nature, appreciates the new results. “This is not the final answer, but it is best suited for this particular mode of formation of black holes,” he says. It is also concerned about how close the simulations to the formation of small stars. To form a black hole, the first gases have been collected in a very small area, which would not happen if they were broken in small clusters of stars. If a little to change the conditions of the simulation, a solid seed is formed. “On the other hand, I like their model, I believe her,” adds Brian.
Fulvio Melia, an astrophysicist at Arizona state University, not happy with this theory. “The authors rely on a bunch of unknown physics, like all other assumptions about the formation of massive seeds or the rapid growth of such facilities,” he says. “They need to make specific assumptions about the behavior of dark matter, but we don’t even know what it is.”
The seed of doubt
To finally answer the question about how these massive animals, scientists point to the future possibility of observation of these “seeds” in the early Universe using the telescopes of the next generation. Such an opportunity soon. Already been several initiatives, such as the ESA mission ATHENA, which is set to launch in 2028 and will be able to capture x-ray emissions of these supermassive giants. Here-here will earn the space telescope James Webb, who will study the first stars and galaxies of the Universe.
“The interesting thing is that these ideas can be checked in the next couple of years, because people will search for these objects all over the sky,” says Melia.
Reset performance: a new model for the birth of supermassive black holes
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