The black holes are very mysterious celestial objects, which never cease to fascinate man. Here is 8 things to know about them, which will help you understand them better.
1. A black hole is not really a hole
Crédit photo: NASA/Dana Berry/SkyWorks Digital
Le black hole is not a hole, at least not quite. Possessing a mass concentrated in a point which one calls gravitational singularity, this mass defines a sphere called horizon of the black hole.
This sphere represents in a way the spatial extension of the black hole. It would therefore be more accurate to think of a black ball if we want to visualize its real physical form in space. On the other hand, its mass is so compact that the intensity of its gravitational field prevents any form of matter or radiation from escaping, hence the term black hole.
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2. You can't see a black hole (but its influence, yes)
Photo credit: NASAJPL-Caltech
Since the black hole does not emit any light, it is difficult to see it. On the other hand, we can observe its effects...
On the one hand, we can observe stars orbiting the black hole, and even determine its mass. Also, the material caught by a black hole is heated before being engulfed, thus emitting a large quantity of X-rays. Several indirect observation techniques make it possible to detect and study these phenomena.
3. There are several kinds of black holes
Un stellar black hole, for example, is a large black hole formed as a result of the gravitational collapse of a massive star. Its mass would thus be equivalent to a few solar masses.
Le supermassive black hole (or black hole galactic) has, for its part, an even greater mass, which can reach several billion times that of the Sun. Researchers also believe that most galaxies have a supermassive black hole at their center that can be up to 40 billion times the mass of the Sun.
There would also be intermediate black holes with a mass of a few thousand solar masses. As for the black holes that would have been formed at the beginning of the history of the Universe, shortly after the Big Bang, they are called primordial black holes.
4. What would happen if we fell into a black hole?
Already, you should know that as you approach the black hole, it will attract you towards it, because of the gravitational force it exerts on the objects around it.
Crédit photo: Thinkstock-SyazwanShahril
Once inside, you would be transformed into spaghetti, literally. Astronomers call this phenomenon spaghettification, which would cause your body to stretch, until it becomes a kind of... noodle.
That said, this effect caused by the gravitational tidal force is all the more important in small black holes. In other words, it is better to dive into a large one, if you absolutely want to...
5. What lies at the heart of the black hole?
Photo credit: Alain r. - Wikipedia
No astronomer knows what really lies at its center, or its famous “singularity”. Why this name? In this region, the gravitational field and the distortions of spacetime (or curvature of spacetime) would become infinite, a concept that defies all the rules, hence the name gravitational singularity.
But according to the researchers, everything that happens in its center is of little importance, since what is inside the zone delimited by the horizon of events, does not influence the outside world… in theory.
6. What goes on around a black hole?
Photo credit: Hubble/Nasa - Wikipedia
Researchers are still observing and trying to understand the jets of matter orbiting around black holes. Although scientists don't all agree, they are probably produced by the huge magnetic field of black holes. These famous jets allow us in any case to better understand black holes, and even to know what they have "swallowed" over the last millennia and also how they were able to form.
Recent discoveries also suggest that jets from supermassive black holes may have contributed to the formation of galaxies...
7. Black, but not so much…
Photo credit: Artist's impression for NASA/ESA
According to a theory by Stephen Hawking, with evaporation, black holes would emit radiation (close to thermal radiation), also called Hawking radiation, thus going against the very concept of the black hole!
The Hawking radiation would in fact be a black body spectrum associated with the "temperature" of the black hole, inversely proportional to its size. In other words, the more massive the black hole, the lower its temperature and the weaker this radiation would be. However, for the moment, it cannot be detected, except perhaps in the case of microscopic black holes as could have been created during the Big Bang (primordial black towers).
8. Can we travel through a black hole?
Photo credit: Artist's vision of wormholes (Les Bossinas) for NASA
Can we travel through a black hole like in the movie Interstellar or The Stargate? In fact, do not confuse black hole and wormhole. The latter, could allow in a completely hypothetical way, a passage through space-time or from one galaxy to another. However, even if we managed to approach this tunnel and enter it, it might close in on us.
While waiting to test the thing, we can continue to contemplate the idea through works of science fiction or simply observe black holes devouring stars...