MattA147 said:
Hey guys, in class today we learned about the life cycle of a star and at the very first stage gravity pulls the helium or Hydrogen nuclei at such a speed that they fuse (nuclear fusion). As I understand it there is little gravity in space so where is this extra gravity coming from?
Thanks for any help given. :)
Here's a 21 second video
it is based on computer simulation of what is called "structure formation"
Stuff starts out almost perfectly uniform, a gas which is everywhere almost equal to its average density. Only some spots where accidentally it is slightly more dense or less dense than average.
surrounding stuff starts falling towards the overdense regions---so they get denser
and the underdense regions gradually get cleared out and become voids.
You can watch it happen in the YouTube simulation
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what you are seeing is largescale structure formation, like galaxies and clusters of galaxies, not individual stars.
but the general idea of stuff condensing works at smaller scale too.
try googling "structure formation". It is a complicated subject and people study it a lot.
At the level of star formation there are a lot of different effects to take into account. Supernova explosions have been mention. Anything that disturbs a cloud of gas will cause regions of overdensity that can become the nucleus of clumping.
Two gas clouds falling together and colliding can send shocks thru each cloud and start the process. Dark matter plays a role. Radiation pressure plays a (generally disruptive) role.
the main idea is simple: stuff falls together and curdles into clumps. nothing is ever perfectly uniform and even very slight non-unformities can become the seeds of structure.
but the actual practice of running computer simulations that model star formation can be complex because of all the different effects.