What Happens When a Black Hole Is Formed?

Stars

• The sun is a small star as stars go, and as such it will lead a fairly ordinary, pedestrian kind of life, turning into a red giant the size of Earth's orbit a few billion years from now and finally collapsing into a white dwarf. Very massive stars, however, lead much shorter and more violent lives, rapidly burning through their hydrogen fuel. As these stars exhaust their hydrogen supply, they transition to fusion of heavier and heavier elements until at last they reach iron. Fusing iron or heavier elements actually takes up energy instead of releasing it.

Supernova

• Once the star has converted all the fuel in its core to iron, its core is no longer producing heat, and the gigantic star rapidly implodes. The inevitable result is a shattering explosion that releases as much as 10^44 joules of energy -- somewhere on the order of a few quadrillion trillion atomic bombs. The exploding star may emit more light over a few days than the sun will emit in its lifetime. A massive shock wave moving at ~6000 miles per second carries much of the star's mass out into space.

Terminal Collapse

• Following the supernova, all that remains of the star is a dense core composed largely of iron and heavy elements. Its fate depends on its mass. If it has less than 10 times the mass of the sun, it will cease to collapse and become a neutron star because the particles in it can only be packed together up to a certain point, just as you can only fit so many marbles into a box. If it is more than 10 times as massive as the sun, however, the force of gravity will be so strong it will be irresistible, and collapse is unstoppable.

Endless Night

• At some point during this collapse, the star crosses the Schwarzschild radius -- the point at which it has become so dense and the gravity at its surface so strong that the escape velocity exceeds the speed of light. This radius or "event horizon" marks the point of no return. Since nothing in the universe can travel faster than the speed of light, once you are past the event horizon, there is no escape. Inside the black hole, the stellar remnant collapses into a singularity, a point at the center of the black hole containing all the mass from the old stellar core. The singularity has zero volume, so its density is infinite.