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A lop-sided stellar explosion
Posted: 06 August 2010

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The first three-dimensional reconstruction of a stellar explosion has been obtained by astronomers using ESO's Very Large Telescope, showing that the explosion was more concentrated in one particular direction.

Artist impression of material ejected during the SN 1987A explosion, based on the latest observations of the supernova debris, showing two outer rings, one inner ring and the deformed, innermost expelled material. Image: ESO/L. Calçada.

Supernova 1987A is a hotbed for analysis; its proximity in the nearby Large Magellanic Cloud has enabled astronomers to study the explosion of the massive star and the aftermath in great detail. Now, using the advanced optics system of the SINFONI instrument, combined with a technique called integral field spectroscopy, astronomers have been able to reconstruct the finer details of the supernova’s chaotic core.

“Integral field spectroscopy is a special technique where for each pixel we get information about the nature and velocity of the gas,” says Karina Kjær. “This means that besides the normal picture we also have the velocity along the line of sight. Because we know the time that has passed since the explosion, and because the material is moving outwards freely, we can convert this velocity into a distance. This gives us a picture of the inner ejecta as seen straight on and from the side.”

The main result was finding the explosion to be stronger and faster in some directions than others, as predicted by recent computer models of supernovae. The first material ejected from the explosion raced away at some 100 million kilometres per hour, but still took ten years to catch up with another ring of gas and dust previously exhaled by the dying star. Another irregular ring of material, travelling ten times more slowly, can be seen much closer to the heart of the dead star.

“Just how a supernova explodes is not very well understood, but the way the star exploded is imprinted on this inner material,” says Kjær. “We can see that this material was not ejected symmetrically in all directions, but rather seems to have had a preferred direction. Besides, this direction is different to what was expected from the position of the ring.”

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