[mesebrec]

Stars are formed when clouds of gas and dust collapse into themselves.

Either the cloud is big and dense enough to collapse into a star, or it will remain as a cloud.

Our Jupiter was created when, during the collapse, other forces pulled part of the collapsing cloud away from the sun, into a stable orbit.

> Stars form when the dust and gas clouds in a nebula cool, progressively fragment and eventually collapse under their own gravity. The smallest stars are about 80 Jupiter masses, below which the core is not dense enough to fuse hydrogen, but smaller objects can coalesce through the same process, including dimly glowing brown dwarfs – sometimes called failed stars – and, below about 13 Jupiter masses, planetary-mass objects. But theoretical predications suggest that the lower boundary for an object forming through a star-like gravitational collapse is about three to seven Jupiter masses.

https://www.theguardian.com/science/2023/oct/02/jumbos-jupit...

[jl6]

> Either the cloud is big and dense enough to collapse into a star, or it will remain as a cloud.

Why is this? Why can’t a small molecular cloud coalesce into small objects?

[piker]

Gas clouds are made of light molecules that a plant would need a large mass to retain, perhaps. Consider how Earth's gravity isn't strong enough to retain He.

[jl6]

But Jupiter’s gravity is strong enough to retain helium and hydrogen.

[simonh]

After the planet has formed, yes. You need something Jupiter mass to already exist as a dense planet to retain those gases that way though. Before that forms the gases disperse too easily so you never get to the Jupiter mass planet stage.

It's only if the mass of the cloud in it's dispersed state is significantly greater than that of Jupiter that it's gravity is strong enough to prevent it's constituents maintaining dispersal due to their own heat.

[Chris2048]

> Earth's gravity isn't strong enough to retain He.

Escape velocity is dependant on temperature, so Earth gravity can't retain He at Earths temperature - A colder Earth perhaps could.

[standardly]

Light molecules? You mean like, photons?

I kid

[circuit10]

When I first read this I was wondering who He was, I guess you mean helium

[pfdietz]

I suspect it may not be able to cool quickly enough. When a cloud collapses the gravitational potential energy goes into heat, and that heat has to be radiated for the collapse to continue. If the gas is too cold or too low in density it may not (I am guessing) be able to do this fast enough before the cloud is either disrupted or accretes too much additional gas.

[mr_toad]

“An interstellar cloud of gas will remain in hydrostatic equilibrium as long as the kinetic energy of the gas pressure is in balance with the potential energy of the internal gravitational force.“

https://en.wikipedia.org/wiki/Star_formation#Cloud_collapse

[mesebrec]

Don't quote me on this but I think the limiting factor is that gravitational pull needs to be stronger than the expansion of the universe.

[danparsonson]

The expansion of the universe isn't really related to the formation of individual stars.

[mbrumlow]

But it sounded cool.

[danparsonson]

That it did