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Black Holes Discovered In Globular Clusters ... Hubblecast 15: Black Holes Unexpectedly Discovered In Globular Clusters NGC 5139 (Omega Centauri), M15 and G1. --- Please SUBSCRIBE to Science & Reason: • • • --- In general relativity, a black hole is a region of space in which the gravitational field is so powerful that nothing, not even light, can escape. The black hole has a one-way surface, called an event horizon, into which objects can fall, but out of which nothing can come. It is called "black" because it absorbs all the light that hits it, reflecting nothing, just like a perfect black-body in thermodynamics. Quantum analysis of black holes shows them to possess a temperature and Hawking radiation. Despite its invisible interior, a black hole can reveal its presence through interaction with other matter. A black hole can be inferred by tracking the movement of a group of stars that orbit a region in space which looks empty. Alternatively, one can see gas falling into a relatively small black hole, from a companion star. This gas spirals inward, heating up to very high temperatures and emitting large amounts of radiation that can be detected from earthbound and earth-orbiting telescopes. Such observations have resulted in the scientific consensus that, barring a breakdown in our understanding of nature, black holes do exist in our galaxy. --- Omega Centauri or NGC 5139 is a globular cluster seen in the constellation of Centaurus, discovered by Edmond Halley in 1677 who listed it as a Nebula. Omega Centauri had been listed in Ptolemy's catalog 2000 years ago as a star. Lacaille included it in his catalog as number I.5. The English astronomer John William Herschel recognized it first as a globular cluster in the 1830s. It orbits our galaxy, the Milky Way. One of the few that can be seen with the naked eye, it is both the brightest and the largest known globular cluster associated with the Milky Way. Omega Centauri is located about 15,800 light-years (4,850 pc) from Earth and contains several million Population II stars. The stars in its center are so crowded that they are believed to be only 0.1 light years away from each other. It is about 12 billion years old. Though it is not a star, Omega Centauri was given a Bayer designation. Unlike other globular clusters, it contains several generations of stars. It has been speculated that Omega Centauri may be the core of a dwarf galaxy several hundred times its present size, which was ripped apart and absorbed by our Milky Way galaxy. Omega Centauri's chemistry and motion in the galaxy is also consistent with this picture. --- Hubblecast features news and Images from the Hubble Space Telescope (HST). The space-based observatory is a collaboration between NASA and ESA. The observations are carried out in visible, infrared and ultraviolet light. In many ways Hubble has revolutionised modern astronomy. The Hubble Space Telescope has made some of the most dramatic discoveries in the history of astronomy. From its vantage point 600 km above the Earth, Hubble can detect light with "eyes" five times sharper than the best ground-based telescopes and looks deep into space where some of the most profound mysteries are still buried in the mists of time. Dr. J is a German astronomer at the ESO. His scientific interests are in cosmology, particularly on galaxy evolution and quasars. Dr. J's real name is Joe Liske and he has a PhD in astronomy. Hubble European Space Agency Information Centre Garching/Munich, Germany • • • .
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