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Probing a New Type of Stellar Explosion
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Probing a New Type of Stellar Explosion

September 13, 2008

Astronomers have been puzzling over the engine behind the historical 1843 outburst of Eta Carinae since it happened, but new observations with the Gemini South and the Blanco telescopes in Chile add a startling new clue. The new observations reveal faint but extremely fast material indicative of a powerful shock wave produced by the 1843 event, suggesting that its driving mechanism was an explosion rather than a steady wind. The research, led by Nathan Smith of the University of California, Berkeley, shows that the famous nebulosity around the star Eta Carinae contains extremely fast-moving filaments of material that had not been seen before, and are not explained by current theories. The result is featured in the September 11, 2008 issue of the journal Nature.

The Gemini spectroscopy, obtained with the Gemini Near-Infrared Spectrometer (GNIRS) helped confirm the high speed and geometry of this material and shows that the 1843 outburst released even more energy than previously estimated. In particular, the high speeds require that the 1843 event generated a shock wave analogous to a supernova-type event, but with less energy. The observations revealed far-flung material moving at more than three times faster than the fastest material seen previously (up to 3,500-6,000 kilometers/second). This work has implications for similar events observed in other galaxies where the resulting outbursts have not quite matched the energy of a supernova, and currently lack any theoretical explanation.

This image is part of a sequence which show's an artist's conception of the expanding blast wave from Eta Carinae's 1843 eruption. The first image shows the star as it may have appeared before the eruption, as a hot blue supergiant star surrounded by an older shell of gas that was ejected in a previous outburst about 1,000 years ago. Then in 1843, Eta Carinae suffered its explosive giant outburst, which created the well-known two-lobed "Homunculus" nebula, plus a fast shock wave porpagating ahead of the Homunculus. New evidence for this fast material is reported here. As time procedes, both the faster shock wave and the denser Homunculus nebula expand and fill the interior of the old shell. Eventually, we see that the faster blast wave begins to catch-up with and overtake parts of the older shell, producing a bright fireworks display that heats the older shell.



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