Black Hole
A Black Hole is a spherical spacetime region with an event horizon (surrounding a very heavy mass with very strong gravitational effects).
- Context:
- It can (typically) form from the gravitational collapse of a massive star after it exhausts its nuclear fuel.
- It can (often) be classified into types such as Stellar Black Holes, Supermassive Black Holes, Intermediate Black Holes, and Primordial Black Holes, based on their origin and mass.
- It can feature an Event Horizon, beyond which nothing, not even light, can escape its gravitational pull.
- It can exhibit Hawking Radiation, a theoretical prediction that suggests black holes emit radiation due to quantum effects near the event horizon.
- It can grow by accreting mass from its surroundings or by merging with other black holes.
- It can significantly affect the structure and dynamics of galaxies, including the formation of Accretion Disks and the emission of high-energy jets.
- ...
- Example(s):
- Sagittarius A*, the supermassive black hole at the center of the Milky Way Galaxy, showcases the significant gravitational influence a black hole can have on nearby stars and gas clouds.
- Cygnus X-1, one of the first suspected black hole candidates, is a stellar black hole formed from the collapse of a massive star and is part of a binary system with a visible star.
- M87*, the supermassive black hole at the center of the Messier 87 galaxy, was the first black hole to be imaged directly, showing the shadow of the black hole surrounded by an accretion disk.
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- Counter-Example(s):
- a Galaxy Nucleus.
- a Supernova.
- a White Dwarf Star.
- a Neutron Star.
- See: Solar Mass, Gravitation, Particle, Electromagnetic Radiation, General Relativity, Mass, Event Horizon, Black Body, Pulsar.
References
2015
- (Wikipedia, 2015) ⇒ http://en.wikipedia.org/wiki/black_hole Retrieved:2015-11-18.
- A black hole is a geometrically defined region of spacetime exhibiting such strong gravitational effects that nothing — including particles and electromagnetic radiation such as light — can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although crossing the event horizon has enormous effect on the fate of the object crossing it, it appears to have no locally detectable features. In many ways a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe.
Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, although its interpretation as a region of space from which nothing can escape was first published by David Finkelstein in 1958. Long considered a mathematical curiosity, it was during the 1960s that theoretical work showed black holes were a generic prediction of general relativity. The discovery of neutron stars sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality.
Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed, it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses () may form. There is general consensus that supermassive black holes exist in the centers of most galaxies.
Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Matter falling onto a black hole can form an accretion disk heated by friction, forming some of the brightest objects in the universe. If there are other stars orbiting a black hole, their orbit can be used to determine its mass and location. Such observations can be used to exclude possible alternatives (such as neutron stars). In this way, astronomers have identified numerous stellar black hole candidates in binary systems, and established that the radio source known as Sagittarius A*, at the core of our own Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses.
- A black hole is a geometrically defined region of spacetime exhibiting such strong gravitational effects that nothing — including particles and electromagnetic radiation such as light — can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although crossing the event horizon has enormous effect on the fate of the object crossing it, it appears to have no locally detectable features. In many ways a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe.