Can the nebular theory be extended to explain the formation of spiral galaxies?
Nebular theory: large cloud of gas and dust that collapses into a swirling disk, creates a massive star at the center and condensing planetesimals around it. Then, the planetesimals combine into planets.
As applied to galaxy: super-massive cloud of gas and dust collapses into a swirling disk with a massive object (black hole) at its center. Then, regions of gas and dust collect into countless smaller objects, which are still massive enough to form stars.
Seems to work, but my astronomy class didn't/hasn't really gone extensively over the formation of galaxies. What is current theory?
Thanks for your help!
You're basically right.
But galaxy formation differs somewhat from star formation, in that the galaxy is mostly dark matter, and the dynamics of the dark matter dominate. The baryonic matter just "comes along for the ride" until it compresses and shocks.
There are two different scenarios for different masses of dark matter halos: adiabatic and isothermal. In smaller galaxies, the infalling gas tends to be isothermal, that is, it cools through radiation as it collapses. In bigger galaxies, the infalling gas heats adiabatically, which mitigates the collapse.
The black hole probably forms after the initial formation of the galaxy, and energy from the black hole likely feeds back and modifies the galaxy formation process.
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