May 13, 2021

What is a black hole?

What is a black hole?

The world knows from this Wednesday how is a black hole, one of the most mysterious and suggestive objects of the Universe, thanks to the image shown by the international Horizon Event Telescope (EHT) consortium.

But what exactly they are, why they fascinate both scientists and non-scientists, who spoke of them for the first time. They are explained to Efe by Roberto Emparan, physicist and researcher ICREA (Catalan Institution of Research and Advanced Studies) of the Institute of Cosmos Sciences of the University of Barcelona.

1. What is a black hole?

A place in space where nothing can escape, not even light.

2. Why do not all stars turn into black holes?

Only very massive stars form black holes. When they exhaust their fuel at the end of their lives, they collapse on themselves in a catastrophic and unstoppable way and in their collapse form a well in space: a black hole.

If they are not so massive, the matter from which they are made can stop the collapse and form a dying star that barely shines: a white dwarf or a neutron star.

3. How many types are there?

Black holes are distinguished by their size. The stars are those that have masses comparable to the Sun and radios of tens or hundreds of kilometers.

Those whose masses are millions or even billions of times the mass of the Sun, are the supermassive black holes of the nuclei of galaxies.

It is also possible that there exist – but we have not yet detected them – intermediate black holes, of hundreds of thousands of solar masses, and primordial black holes, formed at the beginning of the Universe, with masses that could be very small.

4. Why nothing can escape from a black hole?

The force of its gravity is so strong that not even light can escape its attraction. And if light, which is what travels faster in our Universe can not leave, then nothing can.

5. Can they be located anywhere in the Universe?

Yes. We believe that in most galaxies there is a supermassive black hole at its center and hundreds of thousands of stellar black holes.

The known black hole closest to Earth is about 3,000 light-years away from us.

6. What is the event horizon?

The edge of the black hole, the limit beyond which it is impossible to see anything, nor escape from it if one crosses it.

7. Who are the scientists who have contributed the most to knowing about black holes?

Albert Einstein formulated the theory that predicts them, although he never came to understand them or accept them.

Karl Schwarzschild was the first to find a solution to Einstein's equations that describes a black hole (although he died before this was understood).

John Wheeler popularized them and gave them the most successful name in the history of physics.

Stephen Hawking described his properties and left us a paradox when trying to conjugate black holes with quantum physics.

8. Why do they fascinate beyond the scientists?

Black holes uniquely combine elements that we can all share: the fascination of the absolute in these prisons of total darkness, unconditional and definitive; the intrigue about the mysterious destiny of what enters them; the difficulty almost impossible to understand what happens to the time in the black hole.

And also, all this with a name that is the greatest commercial success of science: scientifically appropriate, brief, simple, and even a sexy point.

9. Even the cinema has dared with them, have you told them well?

The first film in which one appears, "The black abyss" (Disney, 1979), is a nonsense in which inside the black hole there are angels and demons. Instead, much of the physics and images of Gargantua, the black hole in "Interstellar" (2014) contain first class science.


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