A brief intro
Many people ask the question : "If a black hole is black , how can you see it ??" If you go to a ball , you see the men dressed in their fancy black suits , and the girls in their lovely white dresses. They dance . but when the lights turn low , you cannot see the men in their black suits , but only the girls in their white dresses. The girls in their white dresses represent the normal stars we see , and the boys in their suits , the black holes. One cannot see the boy ( black hole ) , but by examining the girl ( normal star ) one gets conclusive evidence , that there is something , the boy ( black hole) that keeps the girl ( star) in orbit.
Falling into a black hole
The Astronaut's watch
If one would watch an astronaut jump into a black hole , at some time on his watch , say 12 o'clock , he would cross the event horizon and enter the black hole. But no matter how long you waited , you would never see the astronaut's watch reach 12 o'clock , instead , each second on the watch would appear to take longer until the last second before 12 o'clock would take forever and ever . Thus by jumping into a black hole , one can ensure ones image lasted forever , but the picture would dim very rapidly , that no one would be able to see it.
Watching the Astronaut fall
Falling into a black hole has become one of the horrors of science fiction. In fact black holes can now be said to be matters of science fact , rather than science fiction.
There are good reasons for predicting that black holes should exist and the observational evidence points strongly to a number of black holes in our own galaxy , and more in other galaxies.
A common suggestion is that you can fall through a little hole in space time and out into another region of the universe. This obviously raises great possibilities for space travel. You might set out for a holiday in Virgo , and end up in the crab nebula.
Death in a black hole
Before one looses sight of the outer world one would see things happening , and you would see them happening at a greater rate , almost like a firework display. The frustration is that even though one would be able to see the future it would be going so fast that from a scientific point of view , one would not be able to analyse everything , or take anything in. Eventually things would happen so fast , and become so explosive , that one would perish in the blast.
Surviving a black hole ?
An astronaut who had fallen into a black hole , would come to a sticky end at the singularity real time. However , his particles would continue their hysterisis in imaginary time , but we don't know weather that would be any consolation to the astronaut.
The sun is the size it is , because it is so hot. It is burning hydrogen into helium , like a controlled H – bomb. The heat released in this process generates a pressure that enables the sun to resist the pressure of it's own gravity , which is trying to make it smaller.
The Sun wil eventually run out of nuclear fuel. Luckily this will not happen within the next 5 billion years. Stars with bigger masses' fuel will burn up at a greater rate. This will cause them to loose heat and contract. If the mass of one these stars are less than one and a half times the mass of our sun , they can form a white dwarf , or neutron star. We are able to observe a number white dwarfs not very far from earth.
Neutron stars was discovered in 1967 . when Jocelyn Bell and Antony Hewish , both from Cambridge , discovered objects they called "pulsars". The discovery of neutron stars , was good news for the few scientists who , at that time , believed in black holes. If stars are able to collapse and form neutron stars , neutron stars should also be able to collapse further , to form black holes.
Scientists now have , what they believe , fairly good observational evidence of the existence of several black holes. One of the best cases is believed to be Cygnus X1. This is a binary system , with a normal star rotating around a massive unseen companion.
It seems that matter is being blown off the normal star , falling into the unseen companion. It develops a spiral motion , like water running out of a bath. It gets hot , and gives off the X – rays that we observe. The unseen companion must be very small. It could be a white dwarf , neutron star , or black hole. It is however possible to prove that the mass of the unseen companion should at least be 6 times the mass of our sun.
Looking at these fact , one has to say that it is a black hole , for the mass is too much for it to be a neutron star , or white dwarf.