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View Full Version : Astronomers on Supernova High Alert



Fraser
2005-Sep-12, 11:26 PM
SUMMARY: Supernovae are easy to see - after they've gone off. But it's impossible to find the stars beforehand, so you can study their final moments. Astronomers think they've found a warning sign that a star is about to explode: X-ray flashes. NASA's High-Energy Transient Explorer (HETE-2) has spotted three different powerful blasts of x-ray radiation over the last few weeks, and if astronomers' models hold true, these are precursors to much more powerful gamma-ray bursts, which have been linked with supernovae. Many telescopes around the world will be studying the regions that these x-ray flashes happened, hoping to catch a supernova in the act of exploding.

View full article (http://www.universetoday.com/am/publish/astronomers_supernova_high_alert.html)
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trinitree88
2005-Sep-13, 12:43 AM
I respectfully disagree with the comment that it is impossible to find supernovae before they go off.
There are stars known as reverse novas. They shine at a certain magnitude, dim, and return to their previous visual luminosity....kind of like a Cepheid variable in reverse. R Corona Borealis is such a star. What happens in the case of R Cor. Bor. is that the star puffs off a carbon rich outer layer. The ( soot, buckyballs, whatever...) obscures the star in the visible spectrum. It simultaneously increases the star's infrared output, so that the total bolometric magnitude remains constant....otherwise we'd be inferring a sudden dimming of it's thermonuclear efficiency internally. Not likely.
However, R Cor. Bor. is a massive supergiant, exceeding 8 solar masses, and a type 2 supernova progenitor candidate as well. In the late stages of it's progenitor life, as the star develops an iron core in it's last year pre-supernova...it runs through the curve of binding energy towards iron/nickel. As it changes fuel nuclides, it leaks neutrinos. The neutrino leakiness increases, as heavier and heavier nuclides are burned ever more rapidly to stave off the overpressure. Normally, in other type 2 progenitors, the neutrinos escape undetected into outer space. But in the case of R.Cor.Bor. some of the neutrinos flooding away will scatter in the sooty nebula, transferring momenta and energy to it. So, although the cross-sections (sigma) are low, the flux (phi) becomes prodigious, just before core collapse....and an odd increase in the infrared bolometric magnitude signals the imminent supernova. It was at Williams College, AAPT/APS meeting 1993, that I suggested, during a talk labeled " R Corona Borealis, Infrared Enigma", that somebody take up an observing program of R. Cor Bor. type stars. Southwest Lousiana State did shortly afterward. Patience. Ciao. Pete