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Bright Star Getting Brighter
jwhyche writes "Just what the heck is Eta Carinae doing? Well astronomers are not quite sure. After being one of the brightest stars in the Southern sky it dimmed for a few decades. Now it's back, emiting five time the energy of the sun, and is right next door. So, how big is a hypernova explosion anyways? Big boom anyone? "
Here is a link. And another, and another. Funky!
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This isn't a very good article. Eta Carinae is merely the closest example of a class of stars known as Luminous Blue Variables (LBVs) which have been found in other galaxies and in the center of our own galaxy, obscured by dust.
When a massive star (more than thirty or forty times the Sun's mass) forms, the luminosity is so high that radiation pressure causes the star to lose mass. In the largest stars there is instability- the luminosity will sometimes increase to a few times its normal level and be emitted at shorter wavelengths humans can see, leading to a several hundredfold increase in visible radiation. This is accompanied by ejection of the star's surface layers.
Eta Carinae is believed to have been a bit brighter than it is now before around 1800, and then it underwent an outburst for a few decades in the mid-nineteenth century, becoming the second brightest star in the sky for a while. The star then faded to the limits of human vision for a while and has recovered somewhat in the twentieth century.
The luminosity of Eta Carinae has (for the past couple of centuries, at least) been tens of thousands of times that of the Sun. Most of the energy is emitted in the far ultraviolet, and the star is also behind a thick screen of dust that blocks most of the light which is visible (around ten percent is believed to get through).
A conventional supernova explosion at this distance would be a very bright star, comparable roughly to the planet Venus (currently visible in the west just after sunset). Supernovae of comparable intensity were seen in 1006, 1054, and 1572, so this is not an uncommon event. Supernovae of this size typically result in a black hole. Since these are not terribly uncommon, the nearest example of a black hole is probably at a distance of only a few hundred light years. The local interstellar medium has been cleared out by a supernova shock wave recently which is believed to be in the Scorpius-Centaurus Association, a group of easily visible stars around 500 light years away.
There are some theories which suggest that maybe large systems might do something more exotic, such as conversion of several solar masses of material into energy by gravitational collapse. This is an attempt to explain bright flashes seen in gamma-ray bursters (you can see one for a few minutes in binoculars from a distance of billions of light years) without having to have the energy come out preferentially in one direction. This competes with other theories in which the energy output of gamma-ray bursters is beamed.
My guess is that gamma-ray bursters are not connected with LBVs because there should be a much higher rate of LBVs dying than observed gamma-ray bursts.
... it happened thousands of years ago. Can't you find some real news? :-)
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