Black holes! Do you know everything about this mysterious thing?
We still know little about these mysterious holes found in space. However, scientists found out many theories about it.
Their existence was proved since the 20th century, but even in the 18th century, John Michell and Pierre-Simon Laplace had supposed that such “objects” could exist.
1 First, what is exactly a black hole?
If you throw an object into the air, it will fall. If you had a cannon capable of launching a ball at 11 km / second which is about 40,000 km / hour; then the ball will escape the Earth’s gravity and will not fall.
The more massive a star is, the more its “speed of release” in which we are able to throw an object from its surface and it won’t fall is higher. If a star with the same size as the Sun but 250,000 times heavier, its release speed would be greater than the speed of light. And since nothing travels faster than light, nothing could escape from this star, not even light. Such a star is called a black hole.
2 And does it exist? A star that is 250000 times heavier than the sun?
Yes. We now know that in the middle of each galaxy there is a huge “Supermassive” black hole. The one at the center of our galaxy is called Sagittarius A*.
It was found by observing the star S2 going in circles around something invisible. In 2002, when it moved closer to the black hole, S2 was moving at 5000 km /s ,almost 2% of the speed of light, an absolutely tremendous speed! And with this fact, we were able to calculate that the black hole Sagittarius A * is about 2.6 million times more massive than our sun.
Some galaxies have central black holes a thousand times more massive than Sagittarius A *. The biggest black hole that scientists know today is the one at the center of the galaxy NGC 1277: it has a mass equivalent to 17 billion Suns! But there are also much smaller black holes, from 3 to 15 suns only: they are called “stellar” black holes, they exist because when a massive star dies, it becomes very small and its release speed increases at the same time. If a massive star doesn’t have more than a few tens of kilometers in diameter, it becomes a black hole.
3 So is it true that black holes suck everything?
Before, we thought that black holes suck everything in space near them , but now we know that black holes devour only a little bit of material, and even eject most of it into space . This seems to contradict what I said before so let me explain:
First, a black hole of a certain mass attracts no more than one star of the same mass. If the Sun was transformed suddenly into a black hole (that’s impossible, but let’s imagine …) , it would be the end of the world, but the Earth and all other planets would continue to rotate completely normally around the Black Sun because it would always have the same mass and it would be in the same place.
Plus, a black hole is small enough, so that a falling object would have a lot of chances to miss it rather than turning around and falling into it. All the objects will end up in an “accretion disc” which is much like the rings of Saturn, but turning around the black hole at a tremendous speed. In addition, the material on this disc becomes extremely hot, hotter than a star, so hot that it emits intense light which is invisible to our eyes: X-rays!
4 The jets?
Scientists do not all agree on the details because what happens near a black hole is very complicated, but they think that the jets are produced by the enormous magnetic field of black holes. It deflects a part of the accretion disc to the north and south poles just before it reaches the Schwarzschild radius, and send it into space like a giant natural particle accelerator. These jets are very interesting because they tell us a lot about black holes.
First they are not regular, and they can’t tell us about what the black hole has devoured in the last thousand years. Parts of the jets that are almost invisible correspond to periods when the black hole was “inactive” because it hardly had anything in its accretion disk.
Then we discovered that what we thought were super massive black holes may be completely wrong. We believed that they were formed by swallowing huge amounts of material of their galaxy. Now, scientists think that they had not enough time to become that big since the Big Bang( 14 billion years ago ). Some of these black holes have been created at the Big Bang. So astrophysicists are wondering now: What if super massive black holes had helped to form galaxies around them through their jets!
5 Finally, what is inside a black hole?
This must be my favorite question, because I can tell you my favorite answer: “it is not known yet, but it is not very important.” Of course physicists have described all kinds of theories to tell us what could happen in the black hole, but as nothing that goes in can goes out, what happens inside has no effect on the outside.
Some people have imagined what was going into a black hole and described it like a “white fountain” but we didn’t see anything similar in the universe that looks like this, so let’s say it is more of science-fiction than real science.