Supernova Rates and Historical Supernovae
Supernova Rates
Supernovae are exceedingly rare. There have only been six observed in our
Galaxy over the last 1,000 or so years (these are referred to as
Historical Supernovae)!
The best guess as to their rate of
occurence are 1 per 25 to 100 years in a galaxy like the Milky Way. That is
in a galaxy of 100 billion stars (or so), you expect to get a few supernovae
per century. This rate is based on observations of external
galaxies. Note that the supernova rate for the Milky Way galaxy for the
last 1,000 years has been much slower than this rate.
The conclusion is that we are due for a nearby (galactic)
supernova which as ole Stirl' put it, would be far out,
man.
Historical Supernovae
The term Historical Supernova simply means a supernova which was
visible with the unaided eye ===> the supernova event occured nearby.
Supernova Remnants:
The great importance of SN1987A is that it is an Historical Supernova
which went off at a time when we were technologically advanced enough to
take advantage of many of the things which it had to offer. We observed
SN1987A through its
(1) gamma-ray, x-ray, ultraviolet, optical, infrared, microwave,
and radio radiations; (2) particle emissions (neutrinos); and (3) perhaps
throught its gravitational radiation.
SN1987A was an ideal testbed for many of our ideas on how supernovae work.
