# By what process do different sized stars form?

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• MikeeMiracle
In summary: My thinking is, surely this pressure/temperature needed for ignition is the same for all stars?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.
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

PeroK
Not all gas clouds are the same size.

russ_watters, stefan r and sophiecentaur
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.

MikeeMiracle said:
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

anorlunda
MikeeMiracle said:
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.

MikeeMiracle said:
My thinking is, surely this pressure/temperature needed for ignition is the same for all stars?
Hi Mikee:

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

MikeeMiracle said:
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" ?

MikeeMiracle said:
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.

## 1. How do stars form?

Stars form through a process called stellar evolution, which involves the collapse of a cloud of gas and dust under its own gravity.

## 2. What determines the size of a star?

The size of a star is determined by its mass. The more mass a star has, the stronger its gravitational pull, causing it to collapse and become hotter and denser.

## 3. How do smaller stars form?

Smaller stars, also known as red dwarfs, form from smaller clouds of gas and dust that do not have enough mass to sustain nuclear fusion in their cores. These stars have a longer lifespan compared to larger stars.

## 4. What is the process for larger stars to form?

Larger stars, also known as supergiants, form from larger clouds of gas and dust with enough mass to sustain nuclear fusion in their cores. These stars have a shorter lifespan compared to smaller stars.

## 5. Can stars of different sizes form in the same cloud?

Yes, it is possible for stars of different sizes to form in the same cloud. This is because the cloud may have regions with varying densities, causing some parts to collapse and form smaller stars while others collapse and form larger stars.

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