Pictures taken from the Hubble telescope: the supernova of nearby star Eta Carinae. This star's mass doomed it to collapsing into a black hole.
The Beginning. . .
Most black holes were created by the violent, yet beautiful, explosion of energy known as a supernova. A supernova signals the death of a star, and can have one of three results: if the remnant left by the explosion is less than 1.4 solar masses, it will become a white dwarf; if it is approximately 1.4 solar masses, it will collapse and become a neutron star; and if the remnant is greater than 3 solar masses, a very intriguing thing happens. Whereas the natural repulsion of neutrons against each other causes a neutron star to stabilize at a certain size, the mass of a forming black hole is so great that its own gravity overcomes this repulsive force, and the mass collapses in on itself. As it collapses, its resistance to gravity becomes less, and it continues to collapse until it has become a point of infinite mass, and according to the Theory of Relativity, a point at which spacetime is infinitely curved. This is known as the singularity.
As the collapsing star shrinks in diameter, it reaches a critical point - the Schwarzschild radius - at which it technically becomes a black hole. An event horizon forms at the Schwarzschild radius, and a photon sphere forms at 1.5 times that distance.
. . .The End
For some time, theorists assumed that black holes could only gain mass, as they do not allow mass or energy to escape them. However, in the early 1970's, Stephen Hawking proposed a theory based on Quantum Physics, which was later proven (this theory is explained more fully on the Related Topics page). Basically, it suggested that space is full of virtual pairs of particles and antiparticles which materialize and instantly destroy each other. Theoretically, the spacetime curvature of a black hole would be enough to separate the two particles, drawing one into the singularity and releasing one as a form of radiation. This is now known as Hawking Radiation. According to Hawking Radiation, black holes radiate energy, and therefore lose mass. The amount of radiated energy is inversely proportional to the mass of the black hole, so the more radiation, the smaller the mass, the smaller the mass, the more radiation. This cycle is supposed to continue until the black hole radiates all of its mass. Some theorize that a very small, stable remnant is left, and some believe that the black hole disappears altogether.
Thus ends the life of a black hole.
