The aftermath of Core-Collapse Supernovae

Abstract

T he lifecycles of stars considerably more massive than the sun show that they end in spectacular events in which the core collapses and the outer parts are ejected in a tremendous explosion. The Rosetta stone for the end states of such stars has been the Crab Nebula and its association with the supernova of 1054 (SN 1054) (Fig. 1). The amorphous radiation from the interior of the nebula was identified as synchrotron radiation from relativistic particles in the 1950’s, but the source of the particles was not known until the discovery of a central pulsar, a rapidly rotating magnetized neutron star, in 1968. The spin-down of the central pulsar, with its 33 msec period, was shown to account for the energetic requirements of the nebula. The synchrotron radiation implies the presence of a relativistic bubble of magnetic fields and particles, which are responsible for sweeping the surrounding stellar ejecta into a shell. In a young (age ~1000 yr) supernova remnant, the pulsar is expected to affect the inner part of the exploded star, while the outer part of the star interacts with the surrounding medium. In the Crab Nebula, we see the inner pulsar bubble, but we have not detected the interaction with the surrounding medium. This has been a long-standing puzzle with the Crab. For many years, the Crab pulsar and the older Vela pulsar were the only pulsars that could be clearly linked to the explosive remnants of supernovae. That situation has recently changed; the number of pulsars with surrounding remnants is greater than a dozen. A combination of factors has allowed this advance, but particularly important has been the launch of X-ray space observatories with excellent spatial resolution and sensitivity (ASCA, Chandra, XMM-Newton). These observations have shown that a young pulsar in a supernova remnant is typically surrounded by a pulsar-generated nebula of relativistic particles and magnetic fields generated by the central pulsar as in the Crab Nebula. In many cases, the interaction with the surrounding medium is also observed. At the same time as these discoveries, there have been advances in our understanding of the final evolution of massive stars and the various types of core collapse supernovae. Core collapse is believed to occur in stars with an initial mass >8 M(, where M( is the mass of the sun. Above that mass, the final outcome depends on the rate of mass loss and the core development at the center of the star. Observations of stellar mass loss and evolutionary studies of massive stars show that mass loss rates increase with increasing initial stellar mass (and luminosity). These differences in presupernova mass loss can be linked to the different supernova types and, ultimately, to the different kinds of core collapse remnants. The aim of this paper is to describe these links and the implications for the end states of massive stars. Full details and references can be found in Chevalier (2005).