Aquí apreciamos en la imagen a la Supernova SN2009bb, que está relacionada con el estallido de rayos gamma, fuente: Noticias de Ciencia y Tecnología.Astrofísica
Extraña Supernova Relacionada Con los Estallidos de Rayos Gamma:
Un equipo de astrónomos ha determinado que cierta supernova reciente es la primera que se observa con propiedades similares a las de un estallido de rayos gamma, pero sin rayos gamma detectables del mismo. El descubrimiento, que se realizó utilizando el radiotelescopio VLA, promete señalar el mejor modo de localizar muchos más ejemplos de estas misteriosas explosiones.
"Creemos que las observaciones de radio pronto serán una herramienta más potente para encontrar este tipo de supernovas en el universo cercano que los satélites de rayos gamma", valora Alicia Soderberg, del Centro para la Astrofísica, gestionado conjuntamente por la Universidad de Harvard y el Instituto Smithsoniano.
La pista reveladora apareció cuando las observaciones de radio mostraron material expulsado por la explosión de la supernova llamada SN2009bb, a velocidades cercanas a la de la luz. Esto caracterizó a la supernova como del tipo de las que se piensa que producen cierta clase de estallidos de rayos gamma.
Cuando las reacciones de fusión nuclear en los núcleos de estrellas muy masivas ya no pueden proporcionar la energía necesaria para sostener al núcleo contra el peso del resto de la estrella, éste se colapsa de manera catastrófica convirtiéndose en una estrella de neutrones o en un agujero negro. El resto de material de la estrella es lanzado al espacio en una explosión de supernova. Durante los últimos años, los astrónomos han identificado un tipo particular de estas supernovas con colapso de núcleo como la causa de una clase de estallido de rayos gamma.
No todas las supernovas de este tipo, sin embargo, producen estallidos de rayos gamma. Sólo lo hace aproximadamente una de cada cien.
En el tipo más común de las supernovas de esta clase, la explosión expulsa material de la estrella hacia afuera en un patrón más o menos esférico, a velocidades que, aunque son elevadas, alcanzan sólo un 3 por ciento de la velocidad de la luz. En las supernovas que producen estallidos de rayos gamma, parte del material eyectado, aunque no todo, se acelera a casi la velocidad de la luz.
Los astrónomos creen que las velocidades ultrarrápidas en estos raros estallidos son causadas por un "motor" en el centro de la explosión de la supernova que se asemeja a una versión a escala reducida de un quásar. El material que cae hacia el núcleo entra en un disco giratorio que rodea a la nueva estrella de neutrones o al nuevo agujero negro. Este disco de acreción produce chorros de material impulsados a una tremenda velocidad desde los polos del disco.
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ASTRONOMERS FIND RARE BEAST BY NEW MEANS
2/09/2010 02:55:00 PM Publicado por Jorge Franchín Etiquetas: Astronomy
For the first time, astronomers have found a supernova explosion with properties similar to a gamma-ray burst, but without seeing any gamma rays from it. The discovery, using the National Science Foundation's Very Large Array (VLA) radio telescope, promises, the scientists say, to point the way toward locating many more examples of these mysterious explosions.
2/09/2010 02:55:00 PM Publicado por Jorge Franchín Etiquetas: Astronomy
For the first time, astronomers have found a supernova explosion with properties similar to a gamma-ray burst, but without seeing any gamma rays from it. The discovery, using the National Science Foundation's Very Large Array (VLA) radio telescope, promises, the scientists say, to point the way toward locating many more examples of these mysterious explosions.
"We think that radio observations will soon be a more powerful tool for finding this kind of supernova in the nearby Universe than gamma-ray satellites," said Alicia Soderberg, of the Harvard-Smithsonian Center for Astrophysics.
The telltale clue came when the radio observations showed material expelled from the supernova explosion, dubbed SN2009bb, at speeds approaching that of light. This characterized the supernova, first seen last March, as the type thought to produce one kind of gamma-ray burst.
"It is remarkable that very low-energy radiation, radio waves, can signal a very high-energy event," said Roger Chevalier of the University of Virginia.
When the nuclear fusion reactions at the cores of very massive stars no longer can provide the energy needed to hold the core up against the weight of the rest of the star, the core collapses catastrophically into a superdense neutron star or black hole. The rest of the star's material is blasted into space in a supernova explosion. For the past decade or so, astronomers have identified one particular type of such a "core-collapse supernova" as the cause of one kind of gamma-ray burst.
Not all supernovae of this type, however, produce gamma-ray bursts. "Only about one out of a hundred do this," according to Soderberg.
In the more-common type of such a supernova, the explosion blasts the star's material outward in a roughly-spherical pattern at speeds that, while fast, are only about 3 percent of the speed of light. In the supernovae that produce gamma-ray bursts, some, but not all, of the ejected material is accelerated to nearly the speed of light.
The superfast speeds in these rare blasts, astronomers say, are caused by an "engine" in the center of the supernova explosion that resembles a scaled-down version of a quasar. Material falling toward the core enters a swirling disk surrounding the new neutron star or black hole. This accretion disk produces jets of material boosted at tremendous speeds from the poles of the disk.
"This is the only way we know that a supernova explosion could accelerate material to such speeds," Soderberg said.
Until now, no such "engine-driven" supernova had been found any way other than by detecting gamma rays emitted by it.
"Discovering such a supernova by observing its radio emission, rather than through gamma rays, is a breakthrough. With the new capabilities of the Expanded VLA coming soon, we believe we'll find more in the future through radio observations than with gamma-ray satellites," Soderberg said.
Why didn't anyone see gamma rays from this explosion? "We know that the gamma-ray emission is beamed in such blasts, and this one may have been pointed away from Earth and thus not seen," Soderberg said. In that case, finding such blasts through radio observations will allow scientists to discover a much larger percentage of them in the future.
"Another possibility," Soderberg adds, "is that the gamma rays were 'smothered' as they tried to escape the star. This is perhaps the more exciting possibility since it implies that we can find and identify engine-driven supernovae that lack detectable gamma rays and thus go unseen by gamma-ray satellites.
"One important question the scientists hope to answer is just what causes the difference between the "ordinary" and the "engine-driven" core-collapse supernovae. "There must be some rare physical property that separates the stars that produce the 'engine-driven' blasts from their more-normal cousins," Soderberg said. "We'd like to find out what that property is.
"One popular idea is that such stars have an unusually low concentration of elements heavier than hydrogen. However, Soderberg points out, that does not seem to be the case for this supernova.(Photo: Bill Saxton, NRAO/AUI/NSF)
Fuente de Información: Noticias de la Ciencia y la Tecnología
Guillermo Gonzalo Sánchez Achutegui
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