Black holes are thought to form from stars or other massive objects if and when they collapse from their own gravity to form an object whose density is infinite: in other words, a singularity. During most of a star's lifetime, nuclear fusion in the core generates electromagnetic radiation, including photons, the particles of light. This radiation exerts an outward pressure that exactly balances the inward pull of gravity caused by the star's mass.
As the nuclear fuel is exhausted, the outward forces of radiation diminish, allowing the gravitation to compress the star inward. The contraction of the core causes its temperature to rise and allows remaining nuclear material to be used as fuel. The star is saved from further collapse -- but only for a while.
Eventually, all possible nuclear fuel is used up and the core
collapses. How far it collapses, into what kind of object, and at
what rate, is determined by the star's final mass and the remaining
outward pressure that the burnt-up nuclear residue (largely
iron) can muster. If the star is sufficiently massive or
compressible, it may collapse to a black hole. If it is less massive
or made of stiffer material, its fate is different: it may become a
white dwarf or a neutron star.
Copyright © 1995, The Board of Trustees of the University of Illinois
Black holes are formed when a star dies.Usually, the star is very big, which is at least three times as massive as the sun.All of its mass is squeezed into a single point. At this point, both time and space stop. It's really hard for us to imagine a place like that, but that's how it is in the center of a black hole.
The center of a black hole is called a singularity. Within a distance of the singularity, the gravitational pull is so strong that nothing, not even light, can escape. That distance is called the event horizon. It's like the point of no return.
When people talk about the size of a black hole, they are referring to the size of the event horizon. The more mass the singularity has, the larger the event horizon is.
Many people think that nothing can escape the gravity of a black hole. But if this were true, then the whole universe would be sucked into the black hole. Stars and planets can circle the black hole if they are far enough away from the singularity. Only if things get to close to the singularity they cannot escape.
Black holes are truly black. That makes them extremely hard to detect. When black holes collide with other objects including other black holes, it will ring with a unique frequency, known as its natural mode of vibration. This frequency will tell scientists if they have really detected a black hole. It will also tell them how big the black hole is and how fast it's spinning.-Chris Morris
Gina "Nanogirl" Miller
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