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J. C. Wheeler (University of Texas at Austin)
Evidence concerning the shapes of supernova explosions suggests that those that explode through the process of gravitational collapse are distinctly out-of-round and may typically be "bi-polar," that is to explode along a single axis. This gives clues that the mechanism of explosion may be a magnetohydrodynamic jet associated with the formation of the neutron star. The revolution in the study of cosmic gamma-ray bursts that has followed the discovery of the first optical afterglows has shown that most gamma-ray bursts are at cosmological distances requiring immense power. The power is muted if the gamma-rays are directed in a jet-like fashion. This suggestion of a connection between the physics of supernovae and the physics of gamma-ray bursts is reinforced by the discovery of SN 1998bw that was a bright supernova but a relatively dim gamma-ray burst, circumstantial evidence that gamma-ray bursts arise in rapid star-forming regions suggesting that they are associated with young, massive stars, and evidence for supernova-like brightening in the afterglows of some gamma-ray bursts. Gamma-ray bursts are relatively rare and cannot come from routine supernovae. Major outstanding issues include whether gamma-ray bursts are associated with the birth of black holes or involve neutron star formation and evolution in some way.