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A '''black hole''' is a formation in space with a density so large that its gravitational force causes the escape velocity to exceed the speed of light. Thus, "black" refers to the impossibility of any light ([[photon]]s) escaping, thereby making them completely dark.<ref>They are assumed to come into existence from extremely large stars that collapse into a state of high density when they run out of fusion fuel. An object becomes a black hole when it lies entirely inside the Schwarzschild radius (see below) determined by its mass. For most objects, the Schwarzschild radius is very tiny compared with its size (for Earth it is about 1 centimeter), so the object could not lie inside that radius.</ref>
A '''black hole''' is a formation in space with a density so large that its gravitational force causes the escape velocity to exceed the speed of light. Thus, "black" refers to the impossibility of any light ([[photon]]s) escaping, thereby making them completely dark.<ref>They are assumed to come into existence from extremely large stars that collapse into a state of high density when they run out of fusion fuel. An object becomes a black hole when it lies entirely inside the Schwarzschild radius (see below) determined by its mass. For most objects, the Schwarzschild radius is very tiny compared with its size (for Earth it is about 1 centimeter), so the object could not lie inside that radius.</ref>
Black holes are increasingly promoted by [[liberal]] publications, such as the science page of the ''[[New York Times]]'', glossy magazines, and movies including ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014). Black holes fail the [[falsifiability]] requirement of science, because it is impossible to prove that they do not exist anywhere in the universe. Black holes have an everyday meaning, as in the ''New York Times'' referring to Justice [[David Souter]]'s "chambers as a black hole, from which nothing emerges," a criticism the ''Times'' never voiced again once Souter moved to the pro-[[abortion]] side.<ref>Linda Greenhouse, ''New York Times'' (May 16, 1991). The same article referenced the pendency of a key abortion case on which Justice Souter was the swing vote, and the disparagement of Justice Souter was while the Court was working on its ruling in that case.</ref>
Black holes have become extremely common topics of conversation (as well as scientific discussion, of course) over the last few decades. These discussions are common in such things as the science pages of the ''[[New York Times]]'' and other magazines, and movies including ''Event Horizon'' (1997), ''The Black Hole'' (TV, 2006), and ''Interstellar'' (2014).
Black holes had never been directly observed, and there is no direct evidence for their existence. In early 2019 astronomers released a photo-shopped image of a super-massive black hole located in the galaxy Messier 87 - some 55 million light-years away<ref>https://www.washingtonpost.com/science/2019/04/10/see-black-hole-first-time-images-event-horizon-telescope/</ref>. That alleged black hole has since been informally named "Powehi".<ref>http://time.com/5569262/black-hole-hawaii-powehi/</ref>
Black holes have taken on a very common everyday meaning, as a place from which nothing emerges, as in the ''New York Times'' referring to Justice [[David Souter]]'s "chambers as a black hole, from which nothing emerges," <ref>Linda Greenhouse, ''New York Times'' (May 16, 1991).</ref>
Evidence for the existence of black holes relies on the observations of radiation from accretion disks, motion of stars near the center of the galaxy, and "gravitational lensing," around places where there are no visible objects. Most the evidence for the existence of black holes relies on circumstantial evidence, with heavy reliance on theoretical equations.
Black holes had never been '''directly''' observed, just as electrons, pions, and gamma rays haven't. But, like those other things, evidence for their existence is now incontrovertible. In early 2019 astronomers released an image of a super-massive black hole located in the galaxy Messier 87 - some 55 million light-years away<ref>https://www.washingtonpost.com/science/2019/04/10/see-black-hole-first-time-images-event-horizon-telescope/</ref><ref>https://news.harvard.edu/gazette/story/2019/04/harvard-scientists-lead-team-revealing-black-hole/</ref>. This required gathering data from nine observatories around the world and combining them, using atomic clocks. Like all radio astronomy observations, extensive computer processing was used to produce a visible image. That black hole has since been informally named "Powehi".<ref>http://time.com/5569262/black-hole-hawaii-powehi/</ref>
Evidence for the existence of black holes relies on the observations of radiation from accretion disks, motion of stars near the center of the galaxy, and "gravitational lensing," around places where there are no visible objects.
Because of [[quantum mechanics|quantum-mechanical]] phenomena involving Hawking Radiation, discussed later in the article, black holes must emit radiation and thus are not ''perfectly'' black. Nevertheless, they are called "black holes". Quibbling about this is similar to quibbling about the statement "The Earth is round".
Because of [[quantum mechanics|quantum-mechanical]] phenomena involving Hawking Radiation, discussed later in the article, black holes must emit radiation and thus are not ''perfectly'' black. Nevertheless, they are called "black holes". Quibbling about this is similar to quibbling about the statement "The Earth is round".