What is a black hole?
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Updated June 01, 2013
Black holes are massive objects whose gravitational field is so intense that it prevents any form of matter or radiation to escape.
Black holes are described by the theory of general relativity. When the heart of the dead star is too massive to become a neutron star, it shrinks inexorably to form this mysterious astronomical object, what the black hole.
Stellar black holes have a mass of few solar masses. They arise as a result of the gravitational collapse of massive stars of the residue (about ten solar masses and more).
When the combustion by thermonuclear reactions in the heart of the massive star end for lack of fuel, a supernova occurs.
The latter may leave behind a heart that continues to crumble quickly.
Consideration since the 18th century, the theory supporting the existence of black holes, states that are objects so dense that its escape velocity exceeds the speed of light.
Light can overcome the gravitational force of surface and remains trapped.
The theory also defines precisely the intensity of the gravitational field of a black hole. It is such that no particles crossing the horizon, boundary theory, can not escape.
Image: V. Beckmann (NASA's GSFC) et al., ESA
In search of black holes
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Astronomers have long searched for how quasars, these strange objects, could produce as much energy while being so small. Quasars exist today, they shine so, from a distant past. Relativists advanced explanation of the gravitational collapse.
But what happens there in the extreme conditions of gravitational collapse?
Gravitation Will it compress a huge amount of material in a very small space? In 1939, Einstein believed that it is possible but does not believe that the collapse to reach this critical radius.
Oppenheimer and Schneider show that this can occur, based on rules of general relativity. John Archibald Wheeler was born in 1911, one of the most famous physicist of the 20th century, will oppose the beliefs of Einstein.
Wheeler invents a formula to describe these objects "gravitationally collapsed objects, but the name is too long, he chose the term" black hole ".
The objects that pass near a black hole, are becoming increasingly difficult to move away and gravity becomes increasingly dense until not even light can escape. When the collapse is the most intense, its speed reaches 99% of the speed of light.
Einstein believed that general relativity was pushing too far, that black holes were not real physical objects.
He thought that something, a mysterious force of nature prevented them from forming black holes. Wheeler still exploring this path and supports the ideas of Oppenheimer.
But how to find them since they absorb everything that comes next?
However, many theorists are convinced that the collapse of massive stars can lead to the formation of a black hole and that this collapse could only cause a thermonuclear reaction, which would explode the star. It became necessary to prove the existence of black holes.
A black star who is addressing another, must be analyzed by observing the spectrum of the star visible. If a star rotates around a black hole, it should draw gas from the star.
A new generation of astronomers were looking at the stars around a black hole, those that emit X-ray burst of optical light and radio. They would observe that when a star rotates around an invisible object, the light shifts from red to blue and vice versa. From the speed of this shift, physicists calculate the size of the object. There is mounting evidence and scientists are increasingly convinced that black holes exist. Today, many indications suggest that the center of many galaxies is occupied by a black hole.
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Image: A quasar is a source of energy the most powerful of the universe, a great cauldron of glowing gas that gives off more light than 1,000 galaxies. It is a supermassive black hole, a colossal size as dense as a billion suns, always aspiring stars whole, 1000 masses like the Sun per year.
The center of the Milky Way
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The Milky Way is the central region of our galaxy. Infrared image below shows the cons exact center of our galaxy, known as the Central Molecular Zone and purple, the radio arc of the galactic center.
A number of emission nebulae are visible from the young massive stars that illuminate the interior.
Like almost all galaxies, our galaxy contains at its center, a black hole.
This black hole of several million solar masses, is called Sgr A. The galactic center is also home to the region of star formation, the most active of the galaxy.
The observations in Namibia, with the HESS telescope, have revealed the presence of very energetic gamma rays from the galactic center.
These gamma rays are produced by the collision of protons at very high energy protons with lower energies.
It can occur at that time, a reaction in which neutral meson decays, produce gamma photons.
These photons when they collide with atoms in Earth's atmosphere, producing an avalanche of particles of various kinds are known as cosmic ray showers.
Image: In this picture we see the exact center of our galaxy, known as the Central Molecular Zone and purple, the radio arc of the galactic center.
Besides its scientific interest, this image won first prize in the photographic AUI / NRAO in 2008.
Crédit: A. Ginsburg (U. Colorado - Boulder) et al., équipe BGPS, équipe GLIMPSE II.
Giant ring of black holes
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This stunning composite image of Arp 147, showing two interacting galaxies, located about 430 million light years from Earth. This composite image pink, X-rays taken by Chandra X-ray Observatory at NASA, and optical data (red, green, blue), Hubble Space Telescope, produced by the Space Telescope Science Institute, or STScI. Arp 147 (right) contains the remains of a spiral galaxy, punctured by the collision with the elliptical galaxy located on the left. This meeting has left a wave of stars that stands today as a blue ring, housing young massive stars. In a few million years these stars explode as supernovae, leaving behind, neutron stars and black holes. The nine X-ray sources (pink), scattered around the blue ring in Arp 147, are so bright they could generate black holes, ten to twenty times the mass of the sun. An X-ray source is also visible in the nucleus of the galaxy pink, the center of the image. This source could also be powered by a supermassive black hole.
Other objects, unrelated Arp 147 are also visible on the image, especially in the background, above and left of the galaxy pink, you can see the source of a red quasar. The infrared observations of the Spitzer telescope and ultraviolet observations from NASA Galaxy Evolution (GALEX), were used to estimate the rate of star formation in the ring. From these data, combined with the use of models on the evolution of binary stars, the authors concluded that the stars most intense, have completed their training in approximately 15 million years. These results were published on 1 October 2010 in the Astrophysical Journal. The authors are, Saul Rappaport and Alan Levine of the Massachusetts Institute of Technology, David Pooley Eureka Scientific and Benjamin Steinhorn, also of MIT.
Image: In this image of Arp 147, two galaxies are interacting with many future black holes. Credit: X-ray: NASA/CXC/MIT/S, Rappaport et al., Optical: NASA/STScI
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