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What is a black hole?

Find out what a black hole is and who coined the term.

A black hole is so dense that not even light can escape it. [©Jupiter Images, 2010]
©Jupiter Images, 2010
A black hole is so dense that not even light can escape it.

A black hole is formed when a star with a mass greater than about four times that of the sun collapses. In this event even the neutrons cannot stop the force of gravity. There is nothing to stop the contraction and the star collapses forever in an infinite curvature of time and space known as a singularity.

The material in the singularity is so dense that nothing—not even light—can escape. The American physicist John Wheeler, in 1967, gave this phenomenon the name black hole. Since no light escapes from a black hole, it cannot be observed directly. However, if a black hole existed near another star, it would draw matter from the other star into itself, producing X-rays as a result.

In the constellation of Cygnus, there is a strong X-ray source named Cygnus X-1. It is near a star and the two revolve around each other. The unseen X-ray source has the gravitational pull of at least 10 suns and is believed to be a black hole. Another type of black hole, a primordial black hole, may also exist dating from the time of the Big Bang when regions of gas and dust were highly compressed.

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