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Client_Hello t1_j836l12 wrote

Reply to comment by thomasxin in Why is the Oort cloud spherical? by Outliver

You having it backwards, disks expand to ellipticals as they use up their gas.

Forming a disk requires collisions, and stars are too far apart. The gas in young galaxies does collide, which bleeds off angular momentum, allowing the gas to form a disc, then stars form in the gas.

Those blue stars you see in spiral galaxy arms will not survive a single trip around the core. They light up the region of compressed gas from density waves.

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thomasxin t1_j839eyv wrote

There are smaller blue stars that can still last a billion years or so, right? That would be at least 4 orbits around the milky way for instance. Though larger ones would obviously not last as long

This is an interesting take though, I've not seen sources explaining spiral galaxies evolving into elliptical ones even without disturbance. What would be the cause of the opposite for galaxies, when normal cloud/sphere orbits collapse into rings?

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