As we have had large black holes and the possibility of tiny black holes it would only be fair to mention the creation huge black holes. Known as supermassive black holes, they are found in the centres of galaxies. It is thought that they are black holes created by many other black holes coming together. If two black holes collided it they would not destroy each other or explode, they would simply merge and the radius of the resulting black holes would be larger than either of the two. Supermassive black holes could be created in this way. Another theory states that galaxies formed around black holes and as the galaxy formed the black hole grew by uptake of the matter in the galaxy sized cloud of particles around it.
How do we detect Black Holes?
There are several methods of detection, one is that of mass estimation. This is when stellar objects, such as stars or planets are orbiting what looks like an empty space. It could just be a dim star but with calculations of mass it could be shown that the shadow mass could only be a black hole. This method works well with binary systems, when one of the stars in the system has become a black hole and the system still stands. The star and a point would seems to be orbiting each other.
Although X-Ray telescopes cannot directly see black holes, they can, however, detect the effects of gravity on particles near by. As the particles speed up they get hotter and hotter and begin to radiate. This radiation, emitted by the accretion disk, (the disk of matter which is in orbit about and to be sucked into the black hole,) can be picked up by special telescopes.
Gravity lensing occurs when a black hole comes very near to the path between stars and the Earth. The light flying by the black hole is not always sucked into the hole itself but its path could be distorted. If the path of the light is focused onto Earth then the star will seem to be more luminescent while the black hole is in the correct position.
The last way is more difficult to explain, because I have already stated that even light cannot escape a black hole. But black holes seem to radiate. This radiation is called Hawking Radiation (after Stephen Hawking). To understand this radiation you must understand a little about quantum physics, which states that a vacuum in space is not empty, but dynamically filled with particles and their anti-particle, for example an electron and its anti-particle the positron. This still means that the vacuum maintains is zero energy level as the life of these particles before they annihilate each other is a matter of millionths of millionths of a second. However, if the two particles come into the vacuum near enough to a black hole, then one of the pair could be sucked into the black hole. Due to the fact that the particles should annihilate each other and now cannot, one of the particles becomes a real particle rather than a virtual particle. This particle then escapes the black hole, and it seems that the black hole radiates a particle. This particle is Hawking Radiation, can be detected. We will come to the fate of the other particle in the later stages of this essay.
What happens to the matter?
What happens in a black hole is not a simple matter. There is no evidence of any theory of what happens in a black hole, as any evidence would be promptly lost as it entered the event horizon. The event horizon is the radius of the black hole that is, literally the horizon of events, we cannot see further into the black hole than this radius.
It is known that there are two types of black hole. The Schwarzschild black hole and the Kerr black hole, the difference is that the Schwarzschild type is a non-rotating type, and the Kerr, is a rotating type. Formed from non-rotating and rotating stars, respectively. In the non-rotating type there is no doubt that the matter comes in contact with the singularity. what happens when it does come into contact with the singularity is unknown as the gravity in those conditions is so massive it can be explained as approaching infinite. One approach is that ‘baby universes’ are created.
These would explain a lot about the matter in the black hole itself and the expiration of the black hole, which will be looked at later. Baby universes are could be very important in the explanation of a lot that goes on in our universe, and therefore is quite a valued theory. Within the event horizon of a rotating black hole is probably similar to what happens in a non-rotating black hole, if the matter gets to the singularity, but it is possible to believe that particles fall into the black hole and not hit the singularity. This would be dependant on the speed of rotation of the black hole itself, because the particles from the accretion disk could be thrown past the event horizon in such away that is orbits the singularity. it may then go on to orbit and then fall into the singularity, but it is possible that the black hole dissipates before it reaches the singularity. This theory is helped on by the fact that time travels slower the closer to the singularity you can get. The theory that includes the slowing of time is encompassed in Einstein’s general theory of relativity. The slowing of time explains what you would see if you were watching something falling into the black hole. As the object falls to the event horizon, from an observers point of view it would seem that the object would never enter the hole. This is due to the speed that light is travelling. For the object time would travel normally and within seconds of entering the event horizon (or before) would be ripped to shreds. For the observer the object would never seem to enter the horizon as the time it takes for the light to reach the observer would be getting longer and longer as the gravitation of the hole pulls it back.
Death of a black hole
The death of a black hole is to do with the unsuspecting virtual particle that didn’t get away from the black hole. As it and its anti-particle are supposed to annihilate each other, there is not supposed to be one of the particles left, therefore the particle swallowed by the black hole has negative energy to cancel out the energy that has been created by the escaped particle. Therefore as the black hole has swallowed negative energy it has to lose some mass, following the equation, E=mc2. This occurrence happens as often as a beam of light can cross the black hole itself. Eventually, the black hole will dissipate. At this point all of the gravity will be released and the any light caught in the horizon would be released. Therefore if you observe something falling into the black hole, this is the point in time you would see it finally enter the black hole. However, this is the exact moment that the black hole explodes and so it may be difficult to see. Using calculations involved with Hawking Radiation, a black hole with the mass of our sun would last for 2.1 x 1067. if you remember back to nearer the beginning of this essay it was stated that primordial black holes could be formed, which would be tiny. These tiny black holes, if of the right original mass could be evaporating right now in the universe around us.
Bibliography:
The Centre for Astrophysics and Space Astronomy; www.casa.colorado.edu.
European Space Agency; www.esa.int.
National Aeronautics and Space Administration; www.nasa.gov.
‘Black Hole and Baby Universes and Other Essays’, 1993, S.W Hawking.
‘Universe’, Sixth Edition, R.A Freedman and W.J Kaufmann III.
‘The Hole Man’, 1973, Larry Niven.
