e-Pulsar - Aug

e-Pulsar Aug - Sep 98

Astronomical Feature of the Month
SUPERNOVAE REMNANTS

cygnus loop
The Cygnus Loop, a brilliant HST image.

It's the single most spectacular thing in the life of a galaxy - a supernova. Supernovae occur when a massive star ends its life in an amazing blaze of glory. For a few days, a supernova emits as much energy as an entire galaxy. When it's all over, a large fraction of the star has been blown into space and becomes a supernova remnant. A typical supernova remnant is a few light-years across. They are incredibly complex, with tendrils and filaments of excited gas streaming into space and they glow in every color of the rainbow.

What happens after a star goes supernova depends upon the type and mass of the source star. Most of the time the gas cloud initially expands at rates of up to 10,000 km/s. Gradually the expansion rate slows down while dissipating into the interstellar medium, seeding the neighborhood with heavy elements and providing the necessary shock waves for new stellar formation.

There are two primary types of supernovae:
Type I and Type II.

Type I involve two stars, one of which is a white dwarf with a gravitational attraction so intense that it siphons off material from its companion. When the white dwarf exceeds its stability limit it goes into thermonuclear instability and produces one of the largest explosions known in the Universe.

A Type II supernova involves a single star undergoing core collapse. Gravity condenses hydrogen gas at the center of the star to the point where nuclear fusion is initiated. Hydrogen is fused into helium and energy is given off in the process. As more helium accumulates at the center, the temperature rises due to compression until another nuclear fusion is initiated. This time helium is converted to carbon and oxygen. The fusion process continues, making neon, magnesium, silicon, and sulfur. Finally, iron is created, but here the fusion process stops - it takes more energy to fuse iron than it releases. Under the incredible pressure, the iron core collapses very quickly (within hours or less). Since the iron core can collapse only so far and can no longer undergo fusion, it becomes extremely hot. As everyone knows, hot gases expand rapidly. The star's outer shells rush in to fill the void left by the collapsed iron core and the expanding iron and the collapsing outer gases collide. The result? Tremendous shock waves that blow the outer layers away from the core - the supernova's gigantic explosion.

And quite possibly a wonderful painting or two.....

Quiet Fury
"Quiet Fury" By Joe Tucciarone.
The filaments of gas framing these planets are the tattered remains of a star destroyed in a supernova explosion. The shock wave from the blast has rocked the scarred and pitted worlds of a nearby planetary system.