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Tiny Cannibal Stars - Miniature Versions Of Galactic Centers
Noordwijk, The Netherlands (SPX) Mar 23, 2006 European astronomers said they have solved a mystery concerning vast clouds of superheated gas that whirl around miniature stars in the process of being devoured by the stars' powerful gravitational fields. They said the discovery provides new insight into the eating habits of whole galaxies - as well as these stellar "cannibals." The astronomers, using the XMM-Newton X-ray Observatory, have spied hot-gas clouds ranging in size from a few hundred thousand kilometers to a few million kilometers across - or 10 to 100 times larger than Earth. The orbiting telescope has detected iron vapor and other chemicals in the clouds heated to temperatures of many millions of degrees. "This gas is extremely hot, much hotter than the outer atmosphere of the Sun," said team leader Maria D�az Trigo of ESA's European Science and Technology Research Centre in Noordwijk. XMM-Newton has detected six low-mass X-ray binary star systems within the Milky Way. The paired LMXBs include one tiny core of a dead star, and one Sun-sized companion. Measuring just 15 kilometers to 20 kilometer (10 miles to 13 miles) across and comparable in size to an asteroid, each dead star comprises tightly packed neutrons totaling more than 1.4 times the mass of the Sun. Some 100 known LMXBs populate the Milky Way, each one a stellar furnace, pumping X-rays into space. They represent on a small-scale the accretion process thought to be taking place in the heart of some galaxies. One in every 10 galaxies shows some kind of intense X-ray-generating activity at its center. This activity is thought to be coming from a gigantic black hole, pulling stars to pieces and devouring their remains. Their closer proximity to Earth makes LMXBs easier to study than the active galaxies. The star's extreme density generates a powerful gravitational field that rips gas from the larger and active partner. The gas spirals around the neutron star and forms a disc before being sucked down and crushed onto its surface in a process known as accretion. The clouds sit where the river of matter from the companion star strikes the disc. The extreme temperatures ionize the iron atoms, ripping away almost all of their electrons, giving them very strong electrical charges. Writing in issue no. 445 of the journal Astronomy and Astrophysics, the team said the discovery solves a puzzle that has dogged astronomers for several decades: why certain LMXBs appear to blink on and off at X-ray wavelengths. The reason is these systems appear "edge-on" to Earth-based telescopes. In previous attempts to simulate the blinking, scientists hypothesized clouds of low-temperature gas were orbiting the neutron star, periodically blocking the X-rays, but the resulting models never reproduced the observed behavior closely enough. XMM-Newton solved the mystery by revealing the ionized iron. "It means that these clouds are much hotter than we anticipated," D�az said. With high-temperature clouds, the computer models now simulate the dipping behavior much more closely. "Accretion processes are still not well understood," Diaz said. "The more we understand about the LMXBs, the more useful they will be as analogues to help us understand the active galactic nuclei." Community Email This Article Comment On This Article Related Links XMM Newton ESA Understanding Time and Space
Bs Mesons Lend Clues To Missing Antimatter
Batavia IL (SPX) Mar 23, 2006New preliminary data on the properties of a subatomic particle called a B_s meson suggest that the particle actually oscillates between matter and antimatter � something that if verified could help scientists understand why antimatter is almost nonexistent in the current universe, and perhaps provide the first tangible evidence for the scientific theory called supersymmetry. |
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