March 27, 2023

A black hole doesn’t really have a bottom, because it’s not really a hole. The term ” hole ” is used only to convey the effects of the enormous gravitational attraction it exerts on everything that occurs within its range.

According to the General Theory of Relativity, a black hole is actually a region of space-time “isolated” from the rest of the Universe, in the sense that anything captured by it (including light!) can no longer get out, and the laws of physics that hold without are no longer valid within that region. Basically, we still don’t know exactly what happens to matter when it ends up inside a black hole. Continue to read and find out interesting facts about the black hole.

What is a black hole

A black hole is defined as a region of spacetime with a gravitational field so strong that nothing inside it can escape to the outside, not even light. The idea of ​​the existence of these objects is a corollary of Einstein’s Theory of General Relativity: since the force of gravity, which depends on the mass of the objects, deforms space-time and also curves the trajectory of light, a body can reach concentration of mass so great that its gravitational field prevents even light from moving away.

What size are they?

They are relatively small, although they may compress and enclose the mass of millions or billions of the Sun, black holes are by definition invisible and to make matters more complicated is the fact that these monsters try to hide their own activity. They do this with clouds of dust and swirls of super-hot gas. And yet in this game of deception – and in the gravitational absorption process in which they are the protagonists – they give themselves away: they give off specific radio waves and they are those 1.3 millimeters long captured by radio telescopes.

How are they formed?

The primary formation process for black holes is thought to be the gravitational collapse of heavy objects such as stars.

How many types are there?

For scientists there are three types: the Schwarzschild one, characterized only by mass and formed by the singularity and the event horizon. That of Kerr, which rotates on itself. And finally that of Reissner-Nordstrom, which does not rotate but has an electric charge.

Why are they so important?

Because they are one of the keys to understanding the mysteries of the Universe. While Einstein’s theory describes the universe well, there may be some deviations right near a black hole due to extreme gravity. Thus, Relativity may not be the final theory.

First image of a black hole

And as happened exactly 100 years ago, with the famous photo of the solar eclipse, even today “we are faced with the confirmation of Einstein’s Relativity, ” said project director EHT Shepherd S. Doeleman of the Center for Astrophysics, Harvard & Smithsonian, presenting the image. In reality, the main subject is an absence. A ring structure with a central region from which no photons, i.e. electromagnetic radiation, no form of light arrive. It is the shadow of the black hole at the center of M87, a huge galaxy about 55 million light-years from Earth in the nearby Virgo cluster (and not, as expected, in the center of the Milky Way, Sagittarius A).

The photo showing for the first time the impassable border of a black hole was ‘developed’ thanks to the simultaneous observation of eight radio telescopes around the globe. And after years of observations and analyses, presented in six international press conferences by the Event Horizon Telescope (Eht) project , which involved around sixty scientific institutes around the world, including the National Institute of Astrophysics. Six scientific papers have been published in a special issue of The Astrophysical Journal Letters.

Exactly 100 years have passed since the first image that revolutionized modern physics even in the eyes of the general public. The one taken during the solar eclipse of May 29, 1919 gave the world proof that Einstein’s general theory of relativity was correct. On Sir Arthur Stanley Eddington’s film, stars appeared in a different position from the one they should have occupied: it was proof that the gravitational field of the Sun is also able to bend light, a fundamental prediction of the theory of Relativity.

A telescope as big as the Earth

To observe such a distant and relatively small object, pointing a telescope is not enough, many more are needed, distant from each other. In all, eight to thousands of kilometers from each other, from the Chilean Andes to Hawaii, from Mexico to Spain, from the USA to Antarctica, pointing simultaneously towards the same corner of the cosmos. All together it is as if they formed a single, gigantic parabola, almost as big as the entire planet Earth. The technique used is that of “very long baseline interferometry”. The different radio telescopes are synchronized to an atomic clock, and the data obtained from each has been combined through algorithms that scientists have spent years developing and then running.

10 Interesting facts about the black hole

Black holes evaporate

It’s the theory that made astrophysicist Stephen Hawking , author of the bestseller From the Big Bang to Black Holes, famous all over the world. By applying the laws of quantum mechanics to black holes, children of the theory of relativity, notoriously inapplicable at the quantum level, Hawking demonstrated that black holes aren’t really that black. Eventually, they evaporate. At their event horizon, i.e. the limit between the black hole and the rest of the universe (see point 2), quantum mechanics predicts that particles and antiparticles are continuously created which annihilate each other instantaneously, releasing power. This phenomenon takes place in a vacuum, in every part of the universe; and also on the event horizon of a black hole. Only here something different happens: one particle is captured by the black hole’s gravitational force, the other escapes its attraction. And in doing so it releases energy, and therefore mass, which the black hole loses. Over very long times, billions and billions of years, all their mass evaporates in the form of radiation, and the black hole disappears. At the end of the universe, several eons from now, all matter in the universe, engulfed by black holes, will be released as radiation, the only thing that will exist in the cosmos.

Playing with time

A black hole is characterized by two elements: the central singularity, a point where space-time ceases to make sense; and an event horizon, which surrounds the singularity. It is so called because it represents the horizon beyond which a phenomenon can be observed: an astronaut outside this limit could never see what happens to a colleague who ends up on the other side. And this is because, inside the event horizon, the gravity is such that not even light can get out. However, the astronaut who falls into it could experience a peculiar phenomenon if he is not immediately destroyed by tidal forces. Falling gradually towards the singularity, space-time would dilate to infinite values. The unfortunate astronaut would see in a few moments the future history of the whole cosmos.

At the center of the galaxy

A huge black hole lies at the center of our galaxy. Through the study of the motions of the stars that gravitate around the center, scientists have been able to estimate its size: if the central singularity were in the place of our Sun, its event horizon would extend up to the orbit of Uranus. In billions and billions of years, all matter in the Milky Way will be swallowed up by the central black hole. We know that the Andromeda galaxy also has a similar supermassive black hole at its center, and we suspect that all galaxies have one.

Black holes and origin of the universe

Recent theories claim that supermassive black holes characterized the landscape of the early universe. It is not yet clear how, given that black holes, in most cases, arise from the collapse of stars much larger than the sun. And if in the early universe the stars had not yet had time to die after billions of years of life, where did these come from? The extreme conditions of the first moments after the Big Bang could have had strong consequences on the space-time fabric of our cosmos, leading to the birth of singularities at the center of black holes. But there are also those who argue that our own universe was born from a black hole. And this is because both black holes and the Big Bang share a peculiar element of the theory of relativity, the spacetime singularity, a point of infinite density that could virtually contain the entire universe within itself.

Do small black holes pierce the Earth?

There has been a lot of noise (obviously useless) around the pseudoscientific story that the LHC particle accelerator at Cern in Geneva could have produced mini-black holes the day after it was turned on, in 2008. Small, sure, but capable of engulf the entire planet in no time. It’s actually possible that mini-black holes pass through the Earth practically every day, without us noticing it. Also born at the beginning of the universe, they could have the size of an atom and not be able to swallow anything, due to their peculiar characteristics. But they could be good candidates for explaining dark matter: despite being tiny and invisible, the density at the center of their singularities would be such as to be able to explain that missing mass of the universe that causes astrophysicists around the world to despair.

Space-time tunnels

This last story is known to almost everyone. It is the idea dear to science fiction that it is possible, if disintegration (or β€œ spaghettification ”) inside the black hole is avoided, to use the singularities at their center as space-time shortcuts. By entering a black hole at one point in the universe, we can exit another black hole elsewhere. In reality it is a theory that does not convince physicists very much, even if there are those who have suggested that extraterrestrial civilizations extremely more evolved than us could succeed (or have already succeeded) in artificially producing black holes of this type, stable enough to allows you to use them as wormholes.

The theory of multiverses

Before going any further, it’s vital to know that over the past twenty years many theoretical physicists have come to the conclusion that our universe is not the only one. We may in fact be part of a multiverse, an infinite variety of distinct universes.

How and if one universe is connected to another is still up for debate. However, an interesting theory is that the seed of a universe is similar to the seed of a plant: a small part of essential matter compressed to the maximum level and protected by a shell.

This may be an accurate description of the heart of a black hole. Black holes are all that’s left of stars. When a star runs out of charge, the core collapses inward and gravity grips everything in its merciless grip. The temperature reaches 100 billion degrees, the atoms and electrons are shattered and the residues are further compacted.

Life in a black hole

If we were to use Einstein’s theories to define life in a black hole , we would encounter a hypothetical concept called a singularity. But Einstein’s theories, which provide extraordinary calculations about the cosmos, don’t work with the enormous forces acting inside a black hole.

Physicists like Dr. Poplawski have a theory: the matter inside a black hole reaches a point where it can’t be compacted any further. This “seed” can be incredibly small and weigh as much as a billion suns. But it’s real!

Density of water

This is one of the most incredible things I have ever heard from a professor with whom I found myself discussing black holes in my university days. In fact, we know that these objects, the result of the collapse of a stellar nucleus no longer supported by fusion reactions, generate a very high density, higher than that of nuclear matter and which in all respects is to be considered infinite. This is one of the reasons why we speak of a singularity.

However, if we consider a supermassive black hole, such as those found at the center of galaxies, it is possible to make a different reasoning. In fact, these monsters have a completely different origin, and there are many models in this regard. In any case, for any body to become a black hole it is sufficient for its matter to be compressed below its Schwarzschild radius, proportional to the mass of the black hole.

For this reason, if we calculate the average density of the supermassive black hole based on the ratio between mass and volume (defined by the event horizon ) it may result, for some particularly massive black holes, that it is even lower than that of water . Obviously it is a calculation that leaves the time it finds, since since it is impossible to cross the event horizon and go back, it does not make too much sense to talk about density. In any case, it is a result that from a certain point of view makes an impression and makes us reflect even more on the strangeness of these objects.

Bald or longhaired

Many are used to thinking of black holes as a sort of bottomless pit, which can be described by a single significant parameter, namely their mass, and in which any information that falls into it is lost forever.

In reality, things are not exactly like that. From the “simple” solution of Schwarzschild, in fact, over time we have gone on to obtain more complex solutions for Einstein’s equations, and we have thus come to understand that black holes can be characterized not only by their mass, but also by the charge electric and angular momentum .

This means that, theoretically, black holes are rotating objects with an electromagnetic field and therefore all the information that can be obtained lies in these three parameters. Hence the famous expression ” black holes don’t have hair “, where hair means any type of physical information that is not attributable to the three aforementioned quantities.

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