Astronomy

What is a black hole?

What is a black hole?

To understand what a black hole is, let's start with a star like the Sun, which has a diameter of 1,390,000 kilometers and a mass 330,000 times greater than Earth's.

Taking into account that mass and the distance from the surface to the center, it is shown that any object placed on the surface of the Sun would be subject to a gravitational attraction about 28 times greater than the Earth's gravity on the planet's surface.

A current star retains its normal size thanks to the balance between a very high central temperature, which tends to expand the stellar substance, and the gigantic gravitational attraction, which tends to contract and squeeze it.

If at any given time the internal temperature drops, gravitation will own the situation. The star begins to contract and throughout that process the atomic structure of the interior disintegrates. Instead of atoms there will now be electrons, protons and loose neutrons. The star continues to contract until such time as the mutual repulsion of electrons counteracts any further contraction.

The star is now a "white dwarf." If a star like the Sun suffered this collapse that leads to the state of white dwarf, all its mass would be reduced to a sphere of about 16,000 kilometers in diameter, and its surface gravity (with the same mass, but at a much smaller distance from the center ) would be 210,000 times higher than Earth's.

Under certain conditions the gravitational attraction becomes too strong to be counteracted by electronic repulsion. The star contracts again, forcing electrons and protons to combine to form neutrons and also forcing the latter to crush in close contact. The neutron structure then counteracts any further contraction and what we have is a "neutron star", which could house the entire mass of our sun in a sphere only 16 kilometers in diameter. The surface gravity would be 210,000,000,000 times higher than what we have on Earth.

Under certain conditions, gravitation can overcome even the resistance of the neutron structure. In that case there is nothing that can oppose the collapse. The star can contract to a zero volume and the surface gravity increase towards infinity.

According to the theory of relativity, the light emitted by a star loses some of its energy as it advances against the gravitational field of the star. The more intense the field, the greater the loss of energy, which has been proven experimentally in space and in the laboratory.

The light emitted by an ordinary star like the Sun loses very little energy. The one issued by a white dwarf, something else; and the one emitted by a neutron star even more. Throughout the process of collapse of the neutron star comes a time when the light emanating from the surface loses all its energy and cannot escape.

An object subjected to a compression greater than that of neutron stars would have a gravitational field so intense that anything that approached it would be trapped and could not come out again. It is as if the trapped object had fallen into an infinitely deep hole and never ceased to fall. And since not even light can escape, the compressed object will be black. Literally, a "black hole."

Today astronomers are finding evidence of the existence of black holes in different places in the universe. On April 10, 2019, the first image of a black hole was published, which is in the center of the Messier 87 (M87) galaxy, about 55 million light years away.

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