Eta Carinae and a cool eruption

Feb 17, 2012

Eta Carinae is a massive star system in the southern hemisphere. It is possibly the best studied star system in the sky, attracting the attention of scientists and sky watchers for its fitful dramatic magnitude changes. It even has a place in the tribal oral tales of the aboriginal tribes (Hamacher, D.W. & Frew, D.J. (2010) An Aboriginal Australian record of the Great Eruption of Eta CarinaeJournal of Astronomical History & Heritage, Vol. 13(3), pp. 220-234.). And yet we had it misunderstood by scientists all this time.

Eta Carinae has been known to suffer magnitude variations since the 1600s, but In the mid 1800s it went through a 20 year long, spectacular eruption making it the brightest star in the sky for a while. Now we get to see this eruption again via light echoes! Some of the light from the explosion, originally traveling in a direction away from us, bounced off of a dust sheet and is just now reaching us 170 years later.

Several telescopes, Faulkes Telescope South is among them, have observed this cosmic replay of the Great Eruption, and these observations are shaking our understanding of Eta Carinae. We thought that the Great Eruption was another one of its recurrent outbursts, albeit a more powerful one. Luminous blue variable (LBV) stars, such as Eta Carinae, go through repeated brightening phases. When the radiation pressure is too much to hold the star together with gravity (the Eddington luminosity limit) they shed some of their mass in stellar winds and stabilize again. But the temperature we derive from the light echoes, by studying their spectra, is not consistent with this picture: 5000 K (8500 F) instead of the required 7000 K or more.

So theorists are back to the drawing board: what caused the Great Eruption? Interaction with the companion star in the binary system? A blast wave? Is this explosion unique?

For more information read our article in Nature, Light echoes reveal an unexpectedly cool η Carinae during its nineteenth-century Great Eruption, or watch fellow LCOGT Astronomer, Andy Howell and I talk about the research.

For more details see the UCSB press release.

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Eta Carinae and a cool eruption

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