The nature of supernovae

The obvious association between the Crab Pulsar and the remains of the supernova explosion of AD 1054 leads naturally to the suggestion that all pulsars originate in supernova explosions, and even to the speculation that all supernovae might produce neutron stars, which could become pulsars. This turns out to be an over-simplification, and it is necessary to explore the nature of supernovae in some detail before their relation to pulsars can be pursued.

In 1921 Lundmark pointed out that the nova observed by Hartwig in 1885 in the constellation of Andromeda was probably within the Andromeda Nebula itself, and hence very distant and very bright (see a centenary review by de Vaucouleurs & Corwin 1985). He showed that there were many cases of these extremely powerful novae, and he was the first to associate the Crab Nebula with the Chinese records of the bright star that appeared in AD 1054. The physical significance of these enormous outbursts was appreciated by Baade & Zwicky, who first used the word ‘supernova’ in their publication of 1934. They made four very remarkable deductions from the observations:

1. (1) the total energy released was in the range 1051 to 1055 ergs;

2. (2) the remnant could form a neutron star;

3. (3) cosmic rays could have their origin in supernovae;

4. (4) supernova explosions could give rise to expanding shells of ionised gas.