Explosion Begins to Envelope Star's Surface (image) University of Chicago Share Print E-Mail Caption The hot bubble has broken through the surface of the star, and the top part of it is spreading rapidly across the surface. The spreading material sweeps up unburnt fuel in the surface layers of the star in a compressed layer at its head, much as a snowplow sweeps up fallen snow. By about two seconds, the spreading material will crash into itself at the opposite point on the surface of the star, further compressing and heating the unburnt material, and possibly initiating a detonation. If the collision does produce a detonation, it will propagate through the star at the sound speed, incinerating it in approximately another one to two seconds. The entire nuclear burning phase of the explosion is thus over in approximately three seconds. The energy released by nuclear burning is enough to overcome the pull of gravity, so the material in the star freely expands. The nickel produced during the nuclear burning phase decays first to cobalt and then to iron. These decays emit gamma rays, which heat the expanding envelope of the stellar material, making it glow in the ultraviolet, optical, and infrared portions of the electromagnetic spectrum. This emitted light makes the supernova visible to astronomers on Earth. Credit University of Chicago Flash Center Usage Restrictions This image may be used to illustrate news reports in connection with the findings described in this news release. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.