Why are globular clusters spherical?

[Ags]

Everything else that collapses under gravity forms a disk. Why are globs the exception?

[markse68]

They’re very ancient aren’t they- perhaps they’re just gravitationally clustering ancient wandering stars rather then dark matter enhanced collapsing clouds of active star forming dust and gas? 

Edited January 15, 2022 by markse68
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[iantaylor2uk]

I think disks only form if the gas cloud is rotating - there is a paper online at: https://adsabs.harvard.edu/full/1976ApJ...210..757S which looks at why globular clusters are spherical.

If a gas cloud forms a star then the star is obviously spherical (neglecting rotation), although any other smaller bodies formed around the star are usually in a disk around the star.

[Ags]

I agree the source gas cloud must be rotating, but 100 trillion rotating galaxies suggest that it is very difficult for gas to collape in our universe without rotating - it takes only the slightest nudge or imbalance to start the spinning. I will look at the paper tonight, thanks for that @iantaylor2uk!

Regarding spherical stars and planets - obviously once the matter starts colliding hydrostatic equilibrium will dominate. But even Earth is slightly flattened... isn't that just a special kind of disk? 🤣

Edited January 15, 2022 by Ags

[Ags]

I read the paper... sounds logical. The edges of a disk are more likely to evaporate, leading to a spherical core.