Added 1 new A* page:As I was walking home from a friend's house this evening, gazing idly at the Big Dipper and imagining that I could almost see the supernova at the tip of the northward-facing equilateral triangle you can form from the last two stars in the constellation's "handle," the word "hypernova" popped into my head, so I figured I'd write something about it, because it's a pretty cool word.
A hypernova is simply the explosion of a very large--or "hypergiant"--star: one 100 to 300 times the mass of our Sun. There haven't been very many of these that have been observed well enough to make for pretty pictures, but I did find the case of SN 2006gy, which was, at the time it was discovered in 2006, "the brightest stellar explosion ever recorded" (the next year it was found to have been trumped by one that took place in 2005, but much further away--4.7 billion light years). SN 2006gy took place in galaxy NGC 1260, 238 million light years away, and seems to have been "an unusually high-energy supernova of a very large star, around 150 solar masses." Here is what its X-ray emissions looked like to the Chandra X-ray telescope: that's SN 2006gy's X-ray emissions in the upper right, and all the X-rays from the core of its galaxy in the lower left:
image by NASA/CXC/UC Berkeley/N.Smith (source)
So as you can see, that hypernova of a single star was almost as bright an X-ray source as the entire core of its galaxy!
SN 2006gy is also kind of interesting because scientists have theorized (among other ideas--but this seems to be the front-runner) that its explosion wasn't just the old fashioned kind of supernova, where a star runs out of fuel and collapses, with the collision of its mass resulting in a huge explosion. No! They think that it might have been the first observed pair-instability supernova, which could theoretically happen in stars of between 130 and 250 solar masses. In this case, it wouldn't have been the star running out of fuel that would have led to the explosion; instead, the star would have been in full nuclear swing, and the energy it was emitting--as high energy gamma rays--would have become so intense, due to the star's incredible size, that the gamma rays would, if they struck an atomic nucleus inside the star, contain enough energy to undergo pair production, ie turning from a huge amount of energy into matter: an electron and its opposite, a positron. Einstein's famous E=mc² in action (well, maybe specifically as m=E/c²)!
If that started happening to a lot of the star's energy output, the star would be losing heat (energy) and wouldn't have the bubbling nuclear force to hold itself up--so it would undergo partial collapse. But the sudden pressure increase of this collapse would enable nuclear fusion to burn all the star's fuel in seconds, resulting in a really huge explosion that would blow the giant star entirely apart--not even leaving a super-compressed white dwarf or black hole behind. Also,
| In addition to the immediate energy release, a large fraction of the star's core is transformed to nickel-56, a radioactive isotope which decays with a half-life of 6.1 days into cobalt-56. Cobalt-56 has a half-life of 77 days and then further decays to the stable isotope iron-56. For the hypernova SN 2006gy, studies indicate that perhaps 40 solar masses of the original star were released as Ni-56, almost the entire mass of the star's core regions. Collision between the exploding star core and gas it ejected earlier, and radioactive decay, release most of the visible light. |
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