We imagine black holes as the huge monsters devouring everything on their way. “Big cosmic vacuum cleaners”. Actually they hide a lot. What is inside a black hole? Are the wormholes- time and space travel shortcuts real?
Let’s begin with the last stages of a dying star. A massive star begins to die when it runs out of its internal thermonuclear fuels in its core. After that it starts to shrink inward upon itself under the force of gravity. The outer layers of the star are blown away and the core turns into a point of zero volume and infinite density called the singularity. The border of this singularity called event horizon. Nothing, not even light can escape this singularity which means go through the event horizon. Escape velocity is the speed of light. However, a black hole won’t “suck” you into itself, at least not until you come too close to its gravitational field, event horizon. So if you appear to be floating near such a giant, make sure you are not close enough to the event horizon to be sucked in.
We got all details of the structure of the black holes by calculating the theory of relativity. According to Einstein’s theory of relativity the space-time looks like grid. And objects that have mass make a curvature in it as shown on the image.
Actually not every star after dying turns into a black hole. It depends on the mass of the star. There was one scientists who predicted the existence of stellar bodies that emit no radiation. He predicted it in 1916 and his name was Schwarzchild. Also he predicted a radius of event horizon. Schwarzchild radius is that , foe instance, a star with a mass of 10 our suns will collapse and become a black hole, event horizon of which would be only 30 kilometres. Can you believe it? So the stars no less than 3 masses of our Sun will turn into a black hole after collapsing under its gravity. But if the mass is less, it means the star will become either a white dwarf or a neutron star. Our star- sun, will become a white dwarf according to theories.
” Black hole are black! How can you proof that they even exist?”- you might ask. Well, the answer is pretty easy. Also the black holes are invisible themselves, the effect of their enermous gravitational field on nearby matter is pretty obvious. We can see the envelopes of gas swirling around the black holes at it extremely high velocities.
But there are black hole that are made not after the death of star. There exist black holes that were made in the beginning of the universe and they are small (Hawking). Maybe even died by now.Some of them are made after the collapse of large volumes of interstellar gas. Gas collapses at the centres of quasars or galaxies. One such black hole is Sagittarius A*. This black hole was made of a star with mass of about 4310000 masses of our sun. And this black hole is the centre of our Milky Way galaxy. In 1994 Hubble Space Telescope found a black hole that was a star with more than 6 billion masses of our sun.
Watch this video to get more sense how big black holes can be..