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Martin Wolff's List: Black Holes
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The two galaxies are more than 1.4 billion light-years away from the Milky Way galaxy (a light-year equals about 6 trillion miles). But they are close to each other in cosmic terms -- about as far as the distance from Earth to the center of the Milky Way. That the two appear to be moving toward a merger may have played a role in creating such a powerful jet from the larger galaxy's central black hole. The researchers said that the collision would have no effect on Earth, but the process is one that could play out in our galaxy a billion years into the future. The galaxy Andromeda is the closest to the Milky Way, and the two are gradually coming closer to each other. In time, astronomers say, the two will merge, and the process may cause the dormant central black holes in either the Milky Way or Andromeda to become active and begin sending out similarly powerful jets.
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Using the powerful one-two combo of NASA’s Swift satellite and the Gemini Observatory, astronomers have detected a mysterious type of cosmic explosion farther back in time than ever before. The explosion, known as a short gamma-ray burst (GRB), took place 7.4 billion years ago, more than halfway back to the Big Bang. "This discovery dramatically moves back the time at which we know short GRBs were exploding. The short burst is almost twice as far as the previous confirmed record holder," says John Graham of the Johns Hopkins University, in Baltimore, Md.
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Using a new technique, two NASA scientists have identified the lightest known black hole. With a mass only about 3.8 times greater than our Sun and a diameter of only 15 miles, the black hole lies very close to the minimum size predicted for black holes that originate from dying stars.
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A new discovery has resolved some of the mystery surrounding Omega Centauri, the largest and brightest globular cluster in the sky. Omega Centauri is visible from Earth with the naked eye and is one of the favorite celestial objects for stargazers from the southern hemisphere. Although the cluster is 17,000 light-years away, located just above the plane of the Milky Way, it appears almost as large as the full Moon when the cluster is seen from a dark rural area. Exactly how Omega Centauri should be classified has always been a contentious topic.
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John A. Wheeler, a visionary physicist and teacher who helped invent the theory of nuclear fission, gave black holes their name and argued about the nature of reality with Albert Einstein and Niels Bohr, died April 13, 2008 at his home in Hightstown, N.J. Dr. Wheeler was a young, impressionable professor in 1939 when Niels Bohr, the Danish physicist and his mentor, arrived in the United States aboard a ship from Denmark and confided to him that German scientists had succeeded in splitting uranium atoms. Within a few weeks, he and Bohr had sketched out a theory of how nuclear fission worked. Bohr had intended to spend the time arguing with Einstein about quantum theory, but “he spent more time talking to me than to Einstein,†Dr. Wheeler later recalled. As a professor at Princeton and then at the University of Texas in Austin, Dr. Wheeler set the agenda for generations of theoretical physicists. Max Tegmark, a cosmologist at the Massachusetts Institute of Technology, said of Dr. Wheeler, “For me, he was the last Titan, the only physics superhero still standing.†Among Dr. Wheeler’s students was Richard Feynman of the California Institute of Technology, who parlayed a crazy-sounding suggestion by Dr. Wheeler into work that led to a Nobel Prize. Recalling his student days, Dr. Feynman once said, “Some people think Wheeler’s gotten crazy in his later years, but he’s always been crazy.â€
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A new space mission is going to shed light on some of the most extreme astrophysical processes in nature - including pulsars, remnants of supernovae, and supermassive black holes. The Gamma-Ray Large Area Space Telescope (GLAST) is a four-tonne observatory packed with state-of-the-art particle detectors that will study the gamma-ray sky in unprecedented detail.
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When the universe was still young, they were already dying. The first stars ever to grace the cosmos with light were brutish monsters, so the story believed by most astronomers goes, lumbering clouds of hydrogen and helium hundreds of times more massive than the Sun. They lived fast and bright and died hard, exploding or collapsing into massive black holes less than a billion years after the Big Bang, never to be seen again. But they might have left something behind.
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The black hole is located in the nearby dwarf galaxy IC 10, 1.8 million light-years from Earth in the constellation Cassiopeia. Prestwich’s team could measure the black hole’s mass because it has an orbiting companion: a hot, highly evolved star. The star is ejecting gas in the form of a wind. Some of this material spirals toward the black hole, heats up, and gives off powerful X-rays before crossing the point of no return.
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Like gluttonous piranhas, supermassive black holes in young galaxy clusters gorge on bountiful gas until little fuel is left, and then they fade away, a new study suggests.
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"Active, supermassive black holes were everywhere in the early universe," said Mark Dickinson of the National Optical Astronomy Observatory in Tucson, Ariz. "We had seen the tip of the iceberg before in our search for these objects. Now, we can see the iceberg itself."
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For years, astronomers speculated that a giant, mysterious force lay at the center of the Milky Way, but it wasn't until four years ago that UCLA astronomer Andrea Ghez definitively showed what it was. Using new techniques for peering into the dusty heart of the galaxy, Ghez's observations proved that scores of stars were rapidly orbiting what could only be a black hole. But it wasn't the kind of garden-variety black hole created when a star explodes and dies; it was hundreds of thousands of times as powerful -- a "supermassive" black hole, as they are now known.
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