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  Eta Carinae, probably the raddest star aroundSep 08, 2011 3:03 AM PDT | url
 
Added 1 new A* page:Apparently I should Google my own comic more because I tried it today and found some nice things people said about me some time back! Antionestrife of the I Am Legend blog wrote a very nice review of A* (and they said nice things about the site's navigation system! *swoon* <3) last December. And Beertycoon of the webcomic Maskerman, who has helped me out a few times in the past with feedback on the site, wrote a neat little review of A* on StumbleUpon a while ago. Many belated thanks, guys!
 
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Yesterday I was talking about hypernovas, which are huge supernova explosions that can happen to some of the very biggest stars around. One such star that some have said might be the closest candidate to us for a hypernova is the huge binary (or cluster) Eta Carinae, 7,500 to 8,000 light years away in the Carina Nebula. It is about four million times brighter than the Sun, although 99% of that energy is in the infrared. You can see it as the brightest star (near the top) in this mosaic of the Carina Nebula, taken by the ESO's La Silla Observatory in Chile:
 
Image
image by ESO/IDA/Danish 1.5 m/R.Gendler, J-E. Ovaldsen, C. Thöne, and C. Feron. (source)
 
Eta Carinae used to be even brighter and more massive, though; it is currently believed to be composed of at least two stars: a luminous blue variable ("LBV") of about 100 or 120 solar masses, depending on which source you read (and is believed to have lost an additional 30 solar masses in the past), and a Wolf-Rayet Star of about 30 solar masses; both of these types of stars are so energetic that the radiation they generate overcomes even their massive gravity, and blows their stellar material out into space in vast quantities. The combination of these stars in the Eta Carinae system has shed enough mass to form its own sub-nebula inside the 60-light-year-long Carina Nebula: the smallish but spectacular Homunculus Nebula shrouds the stars in mystery, as you can see in this Hubble mosaic combining red visible light and near-infrared, and adjusting the dynamic range so that you can see both the bright central stars and the cloud around them, which is actually 100,000 times dimmer:
 
Image
image by NASA (source)
 
Most of that cloud is actually thought to have come from a nova explosion in 1841; by 1843, Eta Carinae was the second brightest star in the sky--second only to Sirius, which at just 8.6 light years away is nearly 1000 times closer to us. Scientists can tell that it was an extremely powerful explosion, just short of a supernova that would have destroyed the star, due both to the amount of matter ejected in those nebulous clouds, and to their speed: they are moving outward at 1.5 million miles per hour, or 0.2% the speed of light; but that's less than half the speed of clouds expanding outward from true supernovae. Aside from that peak, Eta Carinae has gone through many cycles of dimming and brightening since its luminosity was first catalogued by Edmond Halley in 1677; these cycles are thought to have to do with fluctuations and eruptions in its stars.
 
In fact, some scientists conclude that the unstable star system is due for its final supernova, or even hypernova, in a "mere" 10,000 to 20,000 years. If it does eventually explode in a hypernova, it might be bright enough to be seen during the day, and its radiation could pose a threat to spacecraft and satellites in Earth orbit. If it shot beams of intense gamma-ray bursts from its poles, as can happen in such explosions, such a beam hitting Earth would subject those on the surface to 10 times the lethal dose of radiation; even if it did go hypernova, though, the chance of it happening to point its gamma ray burst directly at Earth is infinitesimally small--maybe even downright impossible, since its poles don't point in our direction. But don't let little details like that stand in the way of a good doomsday theory!
 
Aside from the extremely unlikely event that it might turn itself into a death ray bent on our destruction, considering that the star types making it up are very rare--there are only 20 known luminous blue variables, and only 300 known Wolf-Rayet stars in our entire galaxy--we're very lucky to have such a cool star system so close by to observe. I suppose I might not be saying that if it did explode and knock out satellites and cable TV and the internet, and maybe screw up the ozone layer a bit more than we are already doing...but come to think of it, that explosion would probably look totally rad. Besides, in 10,000 to 20,000 years, humanity will probably have way bigger problems on its hands. =p
 
 
 
 
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