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  Ask an Astrophysicist  The Question  (Submitted February 08,
1998)  Approximately how much do supernovae expand when they
blow up?  The Answer  A supernova remnant can become very large,
but depends on its age. There are large bubbles of hot gas
within our galaxy that extend for hundreds of light years from
older supernovae. The Crab Nebula, which is believed to have
been formed from a supernova in 1054, is currently expanding at
1450 km/s which, after a little hand waving math, makes it
roughly five light years in radius (assuming a constant
expansion velocity, which is not correct in the early phase of
the supernova, but is roughly correct over most of the 1,000
year age of this remnant). So had the Crab supernova been at
Alpha Centauri distance when it went off, the blast wave would
be coming at us or recently past us.  Jesse Allen for "Ask an
Astrophysicist"  Previous question Main topic Next question
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