Death Star
Posted on Wednesday 15 November 2006
Eta Carinae and its twin lobes, remnants of the flare up of 1843.
Eta Carinae is also interesting because it's probably the only star in the night sky that could conceivably kill you.
When it was first catalogued by Edmond Halley in 1677, it was an unremarkable star barely visible to the naked eye. But since then it's brightness has fluctuated wildly. In the mid-nineteeth century, Eta Carina briefly became the second brightest star in the sky before falling back to near invisibility. Since the fifties, the star's luminosity has been steadily increasing again and in the late nineties suddenly doubled in brightness.
History of Eta Carinae's fluctuations since its discovery in 1677 until the present. The Y-axis represents the star's magnitude.
Such an event would release an incredible amount of energy in the form of a highly focussed beam of gamma rays. If the Earth happened to be on the path of such a beam, there is a little doubt that it would totally devastate life on this planet. Perhaps it was gamma ray bursts like this that in the past caused one or more of mass extinctions that scar the Earth's history.
The theory behind hypernova gamma ray bursts is that they are radiated from the poles of the star but judging from measurements of the star's radial velocity and the shape of its equatorial disk of debris, it appears that the closest pole is pointing away from us us by at least 47 degrees. If true, this should (hopefully) dramatically attenuate the amount of radiation that would be due to arrive in our direction and at worst only disrupt our satellite communication systems.
Nevertleless, you probably wouldn't want to be a astronaut on a space walk at that moment.
Johannes Hevelius integrated Edmond Halley's southern hemisphere observations into his star atlas of 1690 although he did not consider Eta Carinae to be of sufficient brightness to include. 133 years later, it would become the second brightest star in the sky. A curious aspect of Hevelius' star atlas is that the stars are shown as if they had been projected onto a sphere and looked at from the outside (just like the Brazilian flag [more]). A kind of Aristotelian deity's point-of-view.
Eta Carinae from an Earth-centric point-of-view. This time it appears as part of the large red nebula to the right of the famous Southern Cross. Photograph taken in southern Queensland by Greg Bock.
