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22/6/06 - DJ:

La fuerza magnética de los agujeros negros es lo que atrae a la materia

Astrónomos del observatorio de Rayos X Chandra informaron que han determinado que es la fuerza magnética y no la gravedad lo que empuja la materia dentro de los agujeros negros.
Hasta ahora, la creencia popular sobre los agujeros negros nos decía que es su gravedad lo que provoca que toda la materia que se le acerque sea absorbida dentro de ellos. Pero Jon Miller de la universidad de Michigan, Daniel Proga de la universidad de Nevada y otros colegas dicen que esto no es así, porque un objeto atraído por la fuerza de gravedad de un agujero negro quedaría en órbita indefinidamente si no existiera una forma de disipar el momento angular.

Los agujeros negros que tienen una estrella cercana, tienden a atraer la materia de esa estrella dentro del disco que rodea al agujero negro, y esa materia eventualmente ingresa al agujero negro. Eso permite a los científicos saber que algo está quitándole el momento angular.

Miller y sus colegas encontraron que existe una cierta materia que se está empujando constantemente desde el disco que rodea al agujero negro en un "viento" que es creado por la presión en el disco causada por un campo magnético. El viento en sí mismo transporta lejos el momento angular, permitiendo de esta manera que la materia caiga dentro del agujero negro.

En la imagen puede verse la representación de un artista que demuestra cómo los campos magnéticos pueden producir un viento en GRO J1655-40. La rotación en el disco más acciones magnéticas en el disco puede causar los campos magnéticos, demostrados aquí en esta versión simplificada con líneas negras, que pueden arrollarse hacia arriba como una serpiente. Esto puede resultar en que el gas sea conducido hacia arriba y lejos del disco por la presión creada por los campos magnéticos, dando por resultado el viento observado por el laboratorio de Rayos X Chandra.

Fuentes:
Chandra X-Ray Observatory
Nota en castellano: Abierta.tv
Newsletter de prensa de NASA:

June 21, 2006Erica Hupp/Grey HautaluomaHeadquarters, Washington202-358-1237/0688Megan WatzkeChandra X-ray Center, Cambridge, Mass.617-496-7998RELEASE: 06-245NASA'S CHANDRA SOLVES BLACK HOLE PARADOXBlack holes light up the universe and astronomers may finally knowhow. New data from NASA's Chandra X-ray Observatory show for thefirst time powerful magnetic fields are the key to these brilliantand startling light shows.It is estimated up to one quarter of the radiation in the universeemitted since the big bang comes from material falling towardssupermassive black holes, including those powering quasars, thebrightest known objects. For decades, scientists have struggled tounderstand how black holes, the darkest objects in the universe, canbe responsible for such prodigious amounts of radiation.New X-ray data from Chandra give the first clear explanation for whatdrives this process: magnetic fields. Chandra observed a black holesystem in our galaxy, known as GRO J1655-40 (J1655, for short), wherea black hole was pulling material from a companion star into a disk."By intergalactic standards J1655 is in our backyard, so we can use itas a scale model to understand how all black holes work, includingthe monsters found in quasars," said Jon M. Miller of the Universityof Michigan, Ann Arbor. Miller's paper on these results appears inthis week's issue of Nature.Gravity alone is not enough to cause gas in a disk around a black holeto lose energy and fall onto the black hole at the rates required byobservations. The gas must lose some of its orbital angular momentum,either through friction or a wind, before it can spiral inward.Without such effects, matter could remain in orbit around a blackhole for a very long time.Scientists have long thought magnetic turbulence could generate
carries angular momentum outward, allowing the gas to fall inward.Using Chandra, Miller and his team provided crucial evidence for therole of magnetic forces in the black hole accretion process. TheX-ray spectrum, the number of X-rays at different energies, showedthe speed and density of the wind from J1655\'s disk corresponded tocomputer simulation predictions for magnetically-driven winds. Thespectral fingerprint also ruled out the two other major competingtheories to winds driven by magnetic fields."In 1973, theorists came up with the idea that magnetic fields coulddrive the generation of light by gas falling onto black holes," saidco-author John Raymond of the Harvard-Smithsonian Center forAstrophysics in Cambridge, Mass. "Now, over 30 years later, wefinally may have convincing evidence."This deeper understanding of how black holes accrete matter alsoteaches astronomers about other properties of black holes, includinghow they grow."Just as a doctor wants to understand the causes of an illness and notmerely the symptoms, astronomers try to understand what causesphenomena they see in the universe," said co-author Danny Steeghs,also of the Harvard-Smithsonian Center for Astrophysics. "Byunderstanding what makes material release energy as it falls ontoblack holes, we may also learn how matter falls onto other importantobjects."In addition to accretion disks around black holes, magnetic fields mayplay an important role in disks detected around young sun-like starswhere planets are forming, as well as ultra-dense objects calledneutron stars.NASA\'s Marshall Space Flight Center, Huntsville, Ala., manages theChandra program for the agency\'s Science Mission Directorate. TheSmithsonian Astrophysical Observatory controls science and flight",1]
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friction in a gaseous disk and drive a wind from the disk thatcarries angular momentum outward, allowing the gas to fall inward.Using Chandra, Miller and his team provided crucial evidence for therole of magnetic forces in the black hole accretion process. TheX-ray spectrum, the number of X-rays at different energies, showedthe speed and density of the wind from J1655's disk corresponded tocomputer simulation predictions for magnetically-driven winds. Thespectral fingerprint also ruled out the two other major competingtheories to winds driven by magnetic fields."In 1973, theorists came up with the idea that magnetic fields coulddrive the generation of light by gas falling onto black holes," saidco-author John Raymond of the Harvard-Smithsonian Center forAstrophysics in Cambridge, Mass. "Now, over 30 years later, wefinally may have convincing evidence."This deeper understanding of how black holes accrete matter alsoteaches astronomers about other properties of black holes, includinghow they grow."Just as a doctor wants to understand the causes of an illness and notmerely the symptoms, astronomers try to understand what causesphenomena they see in the universe," said co-author Danny Steeghs,also of the Harvard-Smithsonian Center for Astrophysics. "Byunderstanding what makes material release energy as it falls ontoblack holes, we may also learn how matter falls onto other importantobjects."In addition to accretion disks around black holes, magnetic fields mayplay an important role in disks detected around young sun-like starswhere planets are forming, as well as ultra-dense objects calledneutron stars.NASA's Marshall Space Flight Center, Huntsville, Ala., manages theChandra program for the agency's Science Mission Directorate. TheSmithsonian Astrophysical Observatory controls science and flight
For additional information about the research and images, visit:
http://chandra.nasa.govhttp://chandra.harvard.edu-end-To subscribe to the list, send a message to:hqnews-subscribe@mediaservices.nasa.govTo remove your address from the list, send a message to:hqnews-unsubscribe@mediaservices.nasa.gov",0]
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operations from the Chandra X-ray Center, Cambridge, Mass.For additional information about the research and images, visit:
http://chandra.nasa.govhttp://chandra.harvard.edu-end-

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