Star Formation

[johnbee]

The Earth loses free hydrogen because, I think, the speed of movement of hydrogen molecules is greater than the escape velocity.

So how does a cloud of hydrogen ever become so dense as to form a gas planet or even a star? Of course in space it is colder but equally as clouds colllapse they will warm up, and so lose hydrogen. I heard on a TV program that a supernova will cause new stars to form but they seem a bit too rare to me. I would be grateful if someone could point me in the right direction to find out.

[antoniseb]

Didn't you just ask this same question 6 days ago? Did the answer not satisfy you?

[neilzero]

I just looked at the duplicate thread, and it does not answer the question unless it is in the 3 papers suggested by Tim Thompson.
My guess is very large gas clouds with ten or more solar mass have very little surface area per unit volume, so hydrogen losses (which occur only at the outer surfaces) are small compared to an earth size body even though the gravity at the gas cloud surface is much less than one g. Neil

[antoniseb]

My guess is very large gas clouds with ten or more solar mass have very little surface area per unit volume, so hydrogen losses (which occur only at the outer surfaces) are small compared to an earth size body even though the gravity at the gas cloud surface is much less than one g. Neil

It is also the case that prior to the starless core heating up, most of the Hydrogen in the cloud is very cold.

[johnbee]

I did indeed ask the question (in a longer form) previously - but when I returned after a couple of days the message seemed to have vanished, so I asked it again.

Anyway, thanks for the answer. I can not remember where I got the information about hydrogen not being in the air because it's molecules move faster than escape velocity, but of course if it is not so then that does the trick.

I must have accepted the (false) information so the source must have been believable to me; now that it is suspect I should be able to find out more.