By what process do different sized stars form?

[MikeeMiracle]

TL;DR Summary

By what process do different sized stars form?

So the standard explanation for star formation says we have a disk of gas collapsing into itself until a certain pressure/temperature is reached at which point the star "ignites" and pushes away the rest of the material in the disk.

My thinking is, surely this pressure/temperature needed for ignition is the same for all stars? This line of thinking leads on to all stars being the same size when they first ignite? Using this logic, should all starts not be the same size?

I know I am missing something but doing web searches are only bringing up "how a star forms" answers and no explanations for why we have different sizes of star.

Clearly stars exist in many different sizes and temperatures so...which part of the puzzle am I missing and not taking into account that can explain the multitude of different star sizes? Logic would point to the stars igniting at different points and my previous statement about the pressure/temperature required for ignition being different for different stars...but why would this be so? Surely at the temperatures required, all matter just exists as plasma anyway?

Thanks

 

[Vanadium 50]

Not all gas clouds are the same size.

 

[MikeeMiracle]

No, but surely at the point of ignition the remaining dust and gas gets blown away by the solar wind. So either the giant star does not ignite until more material has gathered or the material gets added after ignition. I am just wondering which one it is or a 3rd option I have missed.

 

[PeroK]

No, but surely at the point of ignition the remaining dust and gas gets blown away by the solar wind. So either the giant star does not ignite until more material has gathered or the material gets added after ignition. I am just wondering which one it is or a 3rd option I have missed.

I think the process is quite complicated. I found this, for example:

http://www-astro.physics.ox.ac.uk/~podsi/klessen_starformation.pdf

 

[Vanadium 50]

No, but surely at the point of ignition the remaining dust and gas gets blown away by the solar wind.

"Surely" is not the case. To expel the remaining gas requires stellar wind energy greater than binding energy. Furthermore, to do this quickly requires a huge amount of power.

 

[Buzz Bloom]

My thinking is, surely this pressure/temperature needed for ignition is the same for all stars?

Hi Mikee:

Sorry, I do not remember where I read about this, and I remember no further details.

Different generations of stars, from eras following none or more of a series of supernovas, have different components which are generated by the supernovas from different components. This difference in star components can change the required pressure/temperature for ignition.

Regards,
Buzz

 

[alantheastronomer]

I know I am missing something but doing web searches are only bringing up "how a star forms" answers and no explanations for why we have different sizes of star.

Have you tried Wikipedia under "star formation" ?

 

[stefan r]

Summary:: By what process do different sized stars form?

So the standard explanation for star formation says we have a disk of gas collapsing into itself until a certain pressure/temperature is reached at which point the star "ignites" and pushes away the rest of the material in the disk...

That is not the standard explanation. Ignition of proton-proton fusion does not start until after the star has been a star for a long time. For a solar mass star with solar metalicity the luminosity is higher than solar luminosity for over a million years. It takes about 10 million years before a switch from the Hayashi track to the Henyay track. The solar mass star will be around 4000K but shrinking for those 10 million years.

For the next 90 million years or so (Henyay track) the star is still shrinking but it also rises in temperature so the luminosity is relatively flat. Deuterium, lithium, and 3He fusion confuses things. Even if you had lab made stars between 0.5 and 3.0 solar mass with no fusion fuel you would still have a Henyay track time period but it would be a shorter time period.

The heat radiating out of the protostars comes from gravitational collapse and compression of gas (plasma). The radiative equilibrium during the Hayashi track is a balance between temperature and gravity. Small stars/clouds ramp up to a lower Hayashi temperature and remain in equilibrium there. If you look at the track for K type red dwarfs they start out as a blob with the same temperature it will have when on the main sequence. At 100,000 years old the red dwarf is much larger than the current Sun so its luminosity is still higher despite the lower surface temperature. That is plenty of light pressure to blow out gas and dust.