From what I know about star formation, at its most simplistic, a bunch of gasses begin to amass in space until the gravitational forces within become so great that it kick-starts fusion. Wouldn’t this “event” be a fairly constant across the universe and thereby creating stars of roughly the same size and, for lack of a better term, power? How can stars become, from figures I’ve heard, 2,000 times the mass of our sun? Can they keep collecting mass after they become a star, growing into these “super stars”?
How large a gas cloud can be before it starts collapsing depends on things like the temperature, density, and composition, and all of these vary across space.
Theres an upper limit on star sizes of some 150 solar masses, so 2000 solar masses seems unlikely. Beyond that the radiation pressure created by their collapse is too strong and blows away any excess mass. There are theories that the very early universe had a set of brief lived set of very massive stars, but those are purely theoretical (and I don’t think even those are though to go up to 2k solar masses).
But stars generally form out of molecular clouds, and so their initial mass distribution is thought to mirror the distribution of those clouds. After formation, heavier stars have much briefer lifetimes then ligther ones, so the actual distribution of stars is more weighted towards the lighter end then the mass distribution at the time of their formation.
Kinda like how snowflakes and hailstones and lightning bolts and granite boulders and pebbles are each fairly constant and roughly of the same size? :rolleyes:
I’ve never seen two snowflakes or two lightening bolts where one was 300x the size of the other, which is the level of variation we’re talking about with stars. I don’t think boulders share a common mechanism of formation.
I recently watched the episode of Known Universe that dealt with massive stars, and now that you mention it, I misremembered. I think they said some stars were 2,000 times the mass of Jupiter. That’s a pretty big mistake on my part.
Basically, size is a factor of the ‘amount’ of gasses in the vicinity when they begin to coalesce into an eventual star. In areas of mostly empty space, there are only enough gasses in the vicinity to form a small star. Other areas, more crowded, form into a large star. (And others are too sparse to even form a star, so they gather into gas giant planets like Jupiter & Saturn, or if sparse enough, don’t gather at all and just stay free-floating gas clouds.)
I ran across this while googling around. Interesting read.
Super-petty nitpick: You should have written “Theres an upper limit on stable star sizes of some 150 solar masses…” I remember from a discussion about two months ago that stars beyond 150 solar masses had been detected (or at least a calculated mass assigned) but that they seemed to be in the process of some instability or other, usually a massive stellar wind. This of course doesn’t match the “stellar physics for the layman” write-ups but nonetheless appears tp have been detected. Comment?
No. Molecular clouds aren’t uniform, but even if one started out that way, random movements of the gas particles would quickly change that. The clouds can stay in a state of equilibrium for a long time, where the gravity that holds them together is balanced by the pressure the gas exerts, without stars forming. If the cloud cools, or is disrupted by gravity forces or a supernova shockwave, it will start to collapse. Any densers ares within the cloud will exert a greater gravitational attraction on the surrounding medium, therefore will attract more matter to itself. It’s a runaway process, as more matter is accumulated, the gravitational attraction increases.
For much the same reason, the planets in the solar system aren’t a uniform size either.