Re: Star formation

John Brockbank wrote:

"Sjouke Burry" <burrynulnulfour@xxxxxxxxxxxxxxxxxx> wrote in message news:43fcc0c5$0$2016$ba620dc5@xxxxxxxxxxxxxxxxxxxxxx

John Brockbank wrote:

Sorry if this is an FAQ, but it5 has long made me wonder and I have never seen an explanation.
The Earth massive as it is, is too slight to have hydrogen in the atmosphere. I think that is because the speed of the molecules exceeds, just about, the escape velocity. Given that, how did stars form from hydrogen?

Surface gravity at the sun 27 G?(260 /s/s)
And that is for a yellow dwarf.
Even Jupiter/Saturn/neptune hold onto their
hydrogen pretty well.


Of course once a star has formed it has a strong gravity field. However, presumably a vary large volume of hydrogen, having a huge mass, in fact will have a low gravitational force because it is spread out (inverse square law).

For any given density of material there is some ultimate size beyond which a clump of matter will necessarily and inevitably contract into ever tighter clumps until stars are formed. There are some really nice simulations online at a cosmological scale and star cluster scales too.

Sorry, but I do not think this is a no-brainer.

It only requires that there is enough attractive force from the clump of material to ensure that parts of it slowly become ever denser.

There was a very nice illustrated talk about this at Astrofest by Matthew Bates of Exeter, simulations in video for braodband only at:

http://www.astro.ex.ac.uk/people/mbate/

Regards,
Martin Brown
.