by Doorstop » Tue Jun 08, 2010 5:14 pm
Thread resurrection time. For purely selfish purposes as I don't know the answer to the 'Milndavie question and I've a question of my own ..
A serious one.
I've been watching a fair few astronomy documentaries on the "Dinosaurs and Hitler" section of Sky telly of late and I've been struck by a thought (I know, I know .. "was it lonely?", "did it hurt?", "I've often wondered how things germinate in a desert." etc etc etc .. heard them all before and you can't hurt my rotten feelings).
For some reason there are loads of programmes about stellar formations and the life cycle of stars, their birth, chemistry, gravitational effects, evolution, death of etc and it's become apparent that stars are formed from the coalescence of gases (predominately hydrogen) under gravity, right?
The gases collapse in until the density of hydrogen is such that the resulting heat and pressure forces the hydrogen atoms at the core together so tightly (ie the hydrogen hits a critical mass) that nuclear forces are overcome and two hydrogen atoms fuse together resulting in the formation of a helium atom and a burst of energy.
This in turn causes a cascade reaction in which the star ignites and the resulting shock wave blows away most of the material formed during accretion leaving the burning nuclear reaction at the centre which is the resulting star.
So far, so good.
My question is, given that if hydrogen is elemental and is therefore the same density throughout the universe and the critical mass required for hydrogen to fuse in the core of a protostar is a universal constant, why are stars formed in different sizes?
What I'm trying to say is if it takes a certain amount of hydrogen at a certain density/temperature/pressure to ignite and form the star proper how does a larger amount of hydrogen coalesce to form a larger star without igniting first at a smaller size when it hits critical mass?
Hmm?
I like him ... He says "Okie Dokie!"