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New study says that not all black holes started life as stars

Astrophysicists have found indirect evidence of the formation of black holes which, if confirmed, could enhance our understanding of these stellar phenomena.

A paper published in Astrophysical magazines by researcher Shantanu Basu and Arpan Das of the University of Western Ontario provide evidence that supermassive black holes are possible without a very large star imploding. Rather, the study says that some supermassive black holes grow very rapidly over a very short time and suddenly stop growing. The new model gives scientists an explanation of how black holes were formed during the very early stages of our universe.

"This is indirectly observing evidence that black holes originate from direct collapse and not from star debris," said Basu, an astronomy professor at the University of Western Ontario, in a press release.

Most black holes we know are created in the heart of very large stars, many masses larger than our sun. Stars, by definition, melt smaller atomic nuclei into heavier ones, in processes that create gradually larger and heavier nuclei within the star. In a sufficiently massive star with a very dense core, the gravitational force will eventually overcome the other repelling forces that keep the nuclei apart, which will lead to a spontaneous breakdown in a single point whose flight velocity is greater than the speed of light – by definition, one black hole.

Such collapses tend to be paired with an accompanying massive explosion of the star's outer shell of gas and dust. These explosions create stellar nebulae from which new stars and solar systems form (including our own).

But the presence of supermassive black holes, those over ten or twenty times our solar mass, was a problem for astronomers. How did they form, if not from a single collapsing star? The case of "direct collapse", as Basu and Das provide evidence, suggests that it is possible for a large amount of interstellar gas and dust (not a star) to be spontaneously shot down in an incredibly massive black hole – a much larger one than those created by individual stars that go supernova.

The astronomer Ethan Siegel explained the theoretical process of direct collapse in a Forbes article earlier:

  • A region of space collapses to form stars, while a nearby space area has also undergone gravity collapse but has not yet formed stars.

  • The region with stars emits intense radiation, where the photon pressure keeps the gas in the second cloud from fragmenting to potential stars.

  • The cloud itself continues to collapse, doing so in a monolithic manner. It shows energy (radiation) as it does, but without any stars inside.

  • When a critical threshold is crossed, the large amount, perhaps hundreds of thousands or even millions of times the mass of our Sun, collapses directly to form a black hole.

  • From this massive, early seed, it is easy to get supermassive black holes simply by gravity, merging, accretion and time physics.

"Super-massive black holes only had a short period of time where they could grow quickly and then at some point, because of all the radiation in the universe created by other black holes and stars, so their production ceased," said Basu. "It's the direct collapse scenario."

Over the past ten years, several supermassive black holes that have a billion times more mass than the sun have been discovered. These supermassive black holes are believed to have appeared in our universe 800 million years after the great world – relatively fairly fast, as the galaxies are not believed to have formed until 1 billion years after the Big Bang. These two facts are obviously related, as it is believed that all galaxies have a supermassive black hole in their center around which the rest of the objects in the galaxy break.

These black holes in the early universe have challenged our understanding of their formation and growth in the universe. In March, astronomers announced that they had discovered 83 new supermassive black holes in the early universe that represented a time when the universe was less than 2 billion years old.

It has been a great year for black hole research. On April 10, the Event Horizon Telescope Collaboration (EHT) presented the first ever direct image of a black hole. The blurred composite comprised over two centuries of advances in mathematics, science and electronics. Before the picture, only artistic illustrations were available to depict the mystical singularities that shift the spacetime continuum by virtue of their huge masses and produce such a gravitational force that no light can escape.

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