Q&A: Supernova Remnants and Neutron Stars

Q:
In your web page on "Supernovas and Remnants", you show that a star would be a blue supergiant before it explodes as a supernova. However, in the web page on "Birth of a Neutron Star and Supernova Remnant", you show that the pre-supernova star is a red supergiant. So, which is correct?

A:
Thanks for pointing this out. Both pictures are correct. A star that has a mass of about 10- 25 times the mass of the Sun first becomes a red giant. In most cases it will remain a red giant until it explodes. However, for stars with masses greater than about 20 solar masses, evaporation and radiation pressure may blow off the outer layers of the red giant and transform it into a blue giant before it explodes. The star that exploded to become SN1987A apparently was a blue giant before it exploded.

More on Stellar Evolution is available at http://chandra.harvard.edu/xray_sources/stellar_evolution.html