View Full Version : Could collapsed matter be at the core of nascent planets?

2008-Oct-25, 11:08 PM
How a star is ignited

As the protostar collapses, the interior of the collapsing cloud naturally heats up. As the temperature rises, the speed with which the particles that make up the cloud collide with each other also rises. As the collisions become more energetic, the atoms deep inside the cloud collide so strongly that the electrons are stripped away from all of the nuclei. The gas becomes a completely ionized plasma, a mix of free electrons and free atomic nuclei, the vast majority of which are hydrogen nuclei, which are protons. Eventually, the temperature gets high enough for the protons to stick together. That's when proton fusion begins, and that's when the collapsing cloud becomes a true star.

My bold


My question

Could it not be the case that planets could form similarly, but never reach critical density for fusion proper to kick in?

2008-Oct-26, 10:09 AM
What you've described is a brown dwarf (http://en.wikipedia.org/wiki/Brown_dwarf), a substellar object that is too small for proton-proton fusion to occur (though deuterium fusion may occur).

A even smaller body - for example, a gas giant planet like Jupiter - could theoretically form by cloud collapse without any fusion ever occurring.