Death Star
Posted on Wednesday 15 November 2006 to unknown
Eta Carinae and its twin lobes, remnants of the flare up of 1843.
This is Eta Carinae, the seventh star of the southern Carina
constellation and the most massive and luminous star known in our
galaxy. It's 100 times as massive as our sun and 5 million times
brighter.
Its diameter is about the size of Jupiter's orbit and
it is extremely unstable. Currently it is in the process of rapidly
exhausting its fuel supply and is on the brink of self-destruction. It
could
collapse into itself and form a black hole at any moment.
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.
Stars of this enormity do not last very long because the intensity
of their gravitational fields leads to a rapid consumption of their fusable
hydrogen. Eta Carinae has, at most, only a few
million years to go but it could just as easily self-destruct
tomorrow. When that happens a star would normally explode as a
supernova but such a massive star as this one has the additional
possibility of collapsing in on itstelf and turning into a blackhole.
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. 