Wednesday, June 10, 2009

Betelgeuse is Shrinking: Earth at Grandstand Distance from Supernova?

"Betelgeuse about to blow?"
The Great Beyond ("The Nature blog that rounds up science news from around the world), (June 10, 2009)

"Betelgeuse is shrinking! Could it be about to go supernova? Reports from the American Astronomical Society meeting in Pasadena, California this week suggest that over the past 15 years the bright red star has shrunk by 15%. (Press release)


The blog post does give a number of links, and passes along a tidbit from the UC Berkeley press release: that Betelgeuse is the home star of Zaphod Beeblebrox, a character in "Hitchhiker's Guide to the Galaxy."

The idea that Betelgeuse may explode isn't a crackpot notion. The post quotes Charles Townes, from a "New Scientist" interview: "...Townes tells them: 'Maybe there's some instability in the star and it's going to collapse or at least go way down in size or blow off some material, but who knows.'..."

Grandstand Seats for a Supernova? Exciting!

What makes this rather exciting is the "but who knows." It's possible (although perhaps not all that likely) that we'll have a grandstand seat for a supernova explosion: a never-before-seen even in human history.

That isn't as dangerous as it might seem. I did a little checking, and it looks like the 'kill radius' of a supernova is around 8 pc. "PC" is astronomy-speak for "parsec." One parsec is roughly 3.262 light years. It's "based on the distance from Earth at which stellar parallax is 1 second of arc." (Princeton's WordNet)

For a Supernova, Grandstand Seats are Better Than Front-Row Seating

An abstract of "Supernova Collisions with the Heliosphere" (Brian D. Fields et al, The Astrophysical Journal, American Astronomical Society (April, 2008)) gives a somewhat technical overview of what's likely to have happened, when supernovae went off in Earth's neighborhood. They estimate that, typically, 8 pc, or roughly 26 light years, is the 'kill radius' of a supernova. Closer than that, and matter flowing out from the supernova pushes the solar wind inside Earth's orbit - which might explain some of the mass extinctions over the last billion years.

Bottom line? Looks like we're at a comparatively safe distance. Betelgeuse seems to be about 640 light-years away: almost 25 times the that's-too-close distance.


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