| black hole n. 1. An area of space-time with a gravitational field so intense that its escape velocity is equal to or exceeds the speed of light. 2. A great void; an abyss: The government created a bureaucratic black hole that swallows up individual initiative. |
black hole Astronomy
n
1. (Astronomy) an object in space so dense that its escape velocity exceeds the speed of light
2. any place regarded as resembling a black hole in that items or information entering it cannot be retrieved
| black hole An extremely dense celestial object whose gravitational field is so strong that not even light can escape from its vicinity. Black holes are believed to form in the aftermath of a supernova with the collapse of the star's core. See also event horizon, See more at star. A Closer Look When a very massive star ends its life in a supernova explosion, the remaining matter collapses in upon itself. If there is enough mass in this collapsed star, it becomes a black hole. A black hole is so dense that its gravitational forces are strong enough to prevent anything that comes close enough to the region known as the event horizon from escaping. Even light cannot escape, since the escape velocity (the velocity needed for an object to escape some larger object's gravitational field) necessary to escape a black hole is greater than the speed of light. Black holes are extremely dense: for the Sun, which has a diameter of about 1,390,000 kilometers (862,000 miles), to be as dense as a black hole, its entire mass would have to be squeezed down to a ball fewer than 3 kilometers (5 miles) across. Some theorists postulate that the material in a black hole may be compressed to a single point of infinite density called a singularity. Because astronomers cannot directly observe a black hole, they infer its existence from the effects of its gravitational pull. For example, when a black hole results from the collapse of one star in a binary star system, it attracts material from the remaining star. This material forms an accretion disk, which compresses and heats up until it emits detectable x-rays. Black holes are thought to reside in the centers of many galaxies, including our own Milky Way. |   |
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