Such disks have been found in binary star systems composed of a normal star in a close orbit around a stellar-mass black hole and, on a much larger scale, around the supermassive black holes in the centers of galaxies. Friction between particles in the disk heats them to many millions of degrees, and they produce X-rays. One way to locate black holes is to search for the X-radiation from a disk of hot gas swirling toward a black hole. How do you find black holes with Chandra if you can't see them? Searching for black holes is a tricky business. Matter is heated to millions of degrees as it is pulled toward the black hole, so it glows in X-rays. The X-rays Chandra observes from the vicinity of black holes are from matter that is close to the event horizon of black holes. They may be created when stellar mass black holes merge and gobble up matter in their vicinity, or by the collapse of giant clouds of dust and gas.Ĭan X-ray telescopes see a black hole? No light of any kind, including X-rays, can escape from inside the event horizon of a black hole. The formation of supermassive black holes is more mysterious. To turn the Earth into a black hole, we would have to compress all its mass into a region the size of a marble! Stellar mass black holes are formed when a massive star (more than about 25 times the mass of our Sun) runs out of fuel and its core collapses. How are black holes created? In general, black holes are created whenever enough matter is squeezed into a small enough space. Relativistic jet A powerful jet of radiation and particles traveling close to the speed of light. Singularity A point in the universe where the density of matter and the gravitational field are infinite, as in the center of a black hole. As the gas spirals in due to friction, it becomes hot and emits radiation.Įvent horizon Imaginary spherical surface surrounding a black hole, with radius equal to the Schwarzschild radius, within which no event can be seen heard, or known about by an outside observer. X-ray observations indicate that a large amount of energy is produced in the centers of many galaxies, presumably by the in-fall of matter into a black hole.Īccretion disk A disk of gas and dust that can accumulate around a center of gravitational attraction, such as a normal star, a white dwarf, neutron star, or black hole. High orbital velocities mean that something massive is creating a powerful gravitational field which is accelerating the stars. The evidence comes from optical and radio observations which show a sharp rise in the velocities of stars or gas clouds orbiting the centers of galaxies. Supermassive black holes with the mass of many millions of stars are thought to lie at the center of most large galaxies. the rapidity of the variations in the X-ray emission indicates that they are occurring near the event horizon, or point of no return, around the black hole, and the low intensity of the X-rays suggests that Sagittarius A* is a starved black hole. Chandra’s data of Sagittarius A* and the surrounding area has been referred to as “a gold mine” for astronomers.Ĭhandra also measured the energy output and flaring from Sagittarius A*. Only a few months after its launch, Chandra accomplished what no other optical or X-ray satellite had yet been able to do: separate the emissions from the surrounding hot gas and nearby compact sources that prevented other satellites from detecting this new X-ray source. However, hot gas and charged particles moving at nearly the speed of light produce X-rays that penetrate this shroud. Optical telescopes cannot see through to the center of our Milky Way, which is enshrouded in thick clouds of dust and gas in the plane of the galaxy. Known as Sagittarius A*, this black hole is about 4 million times the mass of the Sun and Chandra has revealed much about its behavior and history. One of the most important black holes to study is the one found at the center of our Milky Way galaxy.
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