Black holes (short version)

Black holes

Black holes are one of science’s most famous objects; they first came from theoretical field, being characterized as general solutions to the general relativity theory. Black holes can only be studied indirectly, that is, analyzing the effects they cause in the medium they are in.

Stellar black holes form when massive stars collapse under their own gravity, compressing a huge amount of matter into a tiny point, called singularity. At that point, science as we know stop working because of such extreme conditions and then the singularity becomes one of the greatest science mysteries.

We know from general relativity that gravity is given by the presence of matter/energy. Because singularity is approximately a point of infinite density, the curvature of space time is such that nothing, not even light (this is why we can’t observe directly a black hole), can escape from being trapped when towards a black hole. Singularities are “covered” with a spherical region called event horizon (which happens to be just a region with a certain distance from singularity), after crossing that frontier, the object is considered to be lost forever. When matter is added to the black hole its size and mass are increased (they absorb anything nearby being considered as universe’s drain).

Another consequence from general relativity is the temporal dilatation. As mentioned, black holes cause a big deformation in the fabric of space time and so time itself for something near the black hole will pass much slower in comparison to someone who is out of the influence of the cosmic devastator.

Studies show that in most spiral and elliptical galaxies there are galactic nucleus, neighborhood of supermassive black holes (in the Milky way we heave Sagittarius A*).

More general, black holes are any points in space where density tends to infinite; that away, if Earth was compressed to just the right amount it would turn into a black hole of approximately the size of a pea.

Even though we can’t obtain information of objects which go beyond the event horizon, we can get three and only three information of any black hole, and those are: mass, angular momentum and electric charge. With that we have an important postulate called no hair theorem. Another curious info we have about black holes was obtained by Stephen Hawking, who showed that black holes emit a kind of radiation called Hawking radiation. After billions of years a given black hole may vanish entirely.

Despite all the mystery involving these curious objects and the evident difficult in studying them, science has shown itself to be powerful, being able to provide information about this matter in the midst of so many obstacles. The great physicist Stephen Hawking dedicated most of his life to the understanding of black holes, taking humanity steps ahead and enlarging our knowledge about the functioning of the cosmos.

Reference material: A brief history of time (Stephen Hawking's book)