Come and learn about black holes
A black hole is a hypothetical celestial body with a gravitational field so strong that not even electromagnetic radiation can escape from its vicinity. The body is surrounded bya spherical boundary, called the event horizon, through which light can enter but can notgo by what appears to be completely black.
A field of these features may correspond to a body of high density with a relatively small mass as the Sun or less, which is condensed into a much smaller volume, or abody of low density with a very large mass, as a collection of millions of stars in thecenter of a galaxy.
The black hole concept was developed by German astronomer Karl Schwarzschild in1916 on the basis of the theory of relativity of Albert Einstein. The radius of the event horizon of a Schwarzschild black hole only depends on the mass of the body: inkilometers is 2.95 times the body mass in solar masses, ie body mass divided by themass of the Sun If a body is electrically charged or rotating, Schwarzschild's results are unchanged. On the outside of the horizon is a "ergosphere", in which matter is forcedto turn to the black hole. In principle, energy can be emitted from the ergosphere.
According to general relativity, gravitation severely modifies space and time near ablack hole. When an observer approaches the event horizon from the outside, timeslows down relative to the observer at a distance, stopping fully in the skyline.
Formation of black holes
Black holes can form during the course of stellar evolution. When nuclear fuel isexhausted in the core of a star, the pressure associated with the heat produced is notenough to prevent the contraction of the core to its own gravity.
In this phase of contraction become important for two new types of pressure. At higher densities a million times that of water, pressure appears due to the high density ofelectrons, which stops the contraction of a white dwarf. This happens for nuclei withmass less than 1.4 solar masses. If the core mass is greater than this amount, thepressure is unable to stop the contraction, which continues until reaching a density ofone trillion times that of water
Then, another new type of pressure due to the high density of neutrons stop the contraction of a neutron star. However, if the core mass exceeds 1.7 solar masses,neither of these two types of pressure is enough to prevent it from sinking into a black hole. Once a body has been made in the radius of Schwartschild theoretically sink orcollapse into a singularity, ie a dimensionless object of infinite density.
In 1994, the Hubble space telescope provided strong evidence that there is a blackhole in the center of the galaxy M87. The high acceleration of gas in this region indicates that there must be an object or group of objects from 2.5 to 3,500 millionsolar masses
English physicist Stephen Hawking has suggested that many black holes may haveformed in the early Universe. If this is so, many of these black holes could be too farfrom other matter to form detectable accretion disks, and could even compose asignificant fraction of the total mass of the universe.
Mass black hole can capture a sufficiently small member of an electron-positron pairnear the event horizon, releasing the other. This particle energy escapes the black hole, causing it to evaporate.
Any black hole formed in the early universe with a mass less than a few billion tonswould have already evaporated, but the greater mass may remain.
In January 1997 a U.S. team of astronomers presented new data on black holes. His research extended to nine binary star systems, X-ray sources (X-ray binaries). In five of the nine cases where the material of the low-mass star hits the surface of anotherobject, it emits a bright radiation on its surface is a neutron star.
In the other four binary, which is believed to contain black holes, the radiation emitted by the second object is minimal: the energy would disappear through the eventhorizon. These data provide the most direct test suite (although not final) of the existence of black holes. The same team of researchers also reported the discoveryof three new candidates for black holes located in the centers of galaxies NGC 3379 (also known as M105), NGC 3377 and NGC 4486B.
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