« on: 22/07/2016 12:28:38 »
Quote from: IAMREALITY
I thought the heat generated by gravity and the particles bumping into each other or whatever is how stars collapse to start the fusion process to begin with?It is thought that today, stars are formed in "stellar nurseries", molecular gas clouds that are a temperature close to absolute zero - perhaps 10K.
Because the gas here is so cold, eddies of gas can condense to form denser aggregations that become protostars and protoplanetary disks. It is thought that this condensation takes millions of years, because collisions of the gas particles heat them up, causing the gas to expand - which opposes the gravitational condensation.
As soon as the star ignites, the heat of radiation and stellar winds blows away most of the protoplanetary disk that hasn't already condensed into planets.
However, in the early universe was still hot after the big bang (ie the CMBR was in the ultraviolet range, not microwaves), so there were no cool clouds of dust that could condense to form protostars and protoplanets; in fact for a considerable time, all atoms were an ionized plasma.
However, the universe was also much smaller and denser soon after the big bang. So if you had enough mass in a small enough volume, you might have eddies that become dense enough to form a black hole, without reaching the extreme densities needed to start hydrogen fusion.
The Jeans Length is an estimate of the size of a gas cloud that could collapse. The size of the cloud is proportional to the square root of the temperature (all other things being equal). So in the early universe, you would need a truly massive cloud.
In this early era, fusion was hard to start, because the universe consisted of Hydrogen & Helium (and a miniscule amount of lithium). There were none of the Carbon, Nitrogen and Oxygen atoms that we see in stellar nurseries today; The CNO Cycle acts as a catalyst to kick-start hydrogen fusion. So this is a barrier to star formation in the early universe.
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