by aichip » Thu Jan 25, 2007 12:10 pm
It is true that when a supernova creates new elements and injects them into space, the cloud is extremely hot and spreads rapidly. However, it is radiating its heat to space until it is nearly as cold as space.
During the expansion phase, the material is driven outward by the explosion and inertia carries it, and since it is still very hot, it cannot contract until it has lost that heat. But when the gas spreads and cools, it can then be diffuse and reach temperatures almost down to 3 Kelvin.
At this point, a shock wave or even a gravitational disturbance can trigger the collapse and condensation of the cloud and this is when star formation begins. And consider that some of the material might already have begun to stick together into small dust particles, and that in this state it is much easier for the collapse to proceed. This is because in this compact state, the heat is more fully lost. Gas that is cold gains heat on compression, of course, but dust grains are already "compressed", being solid matter. At the same temperature, dust would more easily collapse than gas without "rebounding" due to heating.
I suspect that there may be a certain percentage of dust that must be present before star formation can proceed, or that more dust could translate to earlier star formation, due to the cooling that it represents.
It is true that when a supernova creates new elements and injects them into space, the cloud is extremely hot and spreads rapidly. However, it is radiating its heat to space until it is nearly as cold as space.
During the expansion phase, the material is driven outward by the explosion and inertia carries it, and since it is still very hot, it cannot contract until it has lost that heat. But when the gas spreads and cools, it can then be diffuse and reach temperatures almost down to 3 Kelvin.
At this point, a shock wave or even a gravitational disturbance can trigger the collapse and condensation of the cloud and this is when star formation begins. And consider that some of the material might already have begun to stick together into small dust particles, and that in this state it is much easier for the collapse to proceed. This is because in this compact state, the heat is more fully lost. Gas that is cold gains heat on compression, of course, but dust grains are already "compressed", being solid matter. At the same temperature, dust would more easily collapse than gas without "rebounding" due to heating.
I suspect that there may be a certain percentage of dust that must be present before star formation can proceed, or that more dust could translate to earlier star formation, due to the cooling that it represents.