StarDate 4/23/2014: Time Bombs In The Evening Sky

FROM THE UNIVERSITY OF TEXAS McDONALD OBSERVATORY, AS HEARD ON KCBS RADIO WEEKDAYS @ 9:52 A.M., 7:35 P.M. & 2:52 A.M.

STARDATE 4/23/2014: Several ticking time bombs are in view as darkness falls this evening. The list includes most of the bright stars of Orion, which is low in the west: orange Betelgeuse, the three stars of Orion's Belt below it, and Rigel below the belt. And over in the southeast there's Spica, the brightest star of Virgo.

Each of these stars — and several others that are visible to the unaided eye — is destined to explode as a supernova — a blast that can outshine billions of normal stars.

A supernova is bad news for any nearby planet. The explosion can strip away a planet's protective ozone layer and bombard its surface with X-rays, gamma rays, ultraviolet radiation, and other nasty stuff. In fact, some studies have suggested that nearby supernovae could be responsible for mass extinctions distant past.

Most studies put the "danger zone" at anything within a few dozen light-years of the supernova. Betelgeuse and the others are all hundreds of light-years away, though, so they shouldn't be a problem.

The greatest threat to life may come from other types of stars. When these stars explode, they channel jets of particles and radiation into space from their poles. These jets are like massive particle-beam weapons, exterminating any life within tens of thousands of light-years, and perhaps a good bit farther. No known stars in this class are aiming their poles toward Earth, so we appear to be safe from these megablasts.