tomatoherd wrote:But, I can understand formation of a disc galaxy out of a primordial mass/cloud. And its resultant components are mostly orbiting the galaxy's center in the same direction.
Only while the primordial disk structure is maintained. But that's not a stable structure, and the period of reasonable stability is related to the stellar density. So even in a disk galaxy, most of the stars are not orbiting on the same plane or in the same direction. Only in the disk itself do we see that, where the stars are far enough apart that they don't perturb each other much.
But I cannot wrap my head around how an even smaller mass could condense into individual components all moving in random directions (and be still so "unlumpy" after 13 billion years).
This is the lowest energy state for a multiple-body orbiting system. It's what every such system eventually evolves into: a spherical structure, with the components in randomly inclined orbits, and a density gradient from the center to the outside. It's exactly what you get when you numerically model a large number of particles which are gravitationally bound and are controlled only by Newtonian dynamics.
How they initially condense (or form) is an entirely different question, which remains unanswered. But once you have condensed structures, their behavior is understandable, and globulars are well understood in this respect.
But accretion discs move to center, mergers occur in galaxy groups, etc, etc. Why are clusters so stable?
Accretion disks behave as they do because of viscous interactions (electromagnetic forces are important). Galaxies are much more diffuse, and their interactions occur over scales similar to their size (with the greatest part of the disruption occurring in the tenuous outer parts, not the cores). Globular clusters are very compact and located far from their parent galaxies with respect to their sizes. So they are not strongly influenced by tidal forces. They simply aren't exposed to much in the way of external perturbations. So most persist until they evaporate. Some, however, must be disrupted by tidal forces when they orbit too closely to a galaxy, or even come to close to another globular. But those are going to be statistically rare events.
And to me, 13 billion years is a loooong time.
To me, it's "we've only just begun".
[quote="tomatoherd"]But, I can understand formation of a disc galaxy out of a primordial mass/cloud. And its resultant components are mostly orbiting the galaxy's center in the same direction.[/quote]
Only while the primordial disk structure is maintained. But that's not a stable structure, and the period of reasonable stability is related to the stellar density. So even in a disk galaxy, most of the stars are not orbiting on the same plane or in the same direction. Only in the disk itself do we see that, where the stars are far enough apart that they don't perturb each other much.
[quote]But I cannot wrap my head around how an even smaller mass could condense into individual components all moving in random directions (and be still so "unlumpy" after 13 billion years).[/quote]
This is the lowest energy state for a multiple-body orbiting system. It's what every such system eventually evolves into: a spherical structure, with the components in randomly inclined orbits, and a density gradient from the center to the outside. It's exactly what you get when you numerically model a large number of particles which are gravitationally bound and are controlled only by Newtonian dynamics.
How they initially condense (or form) is an entirely different question, which remains unanswered. But once you have condensed structures, their behavior is understandable, and globulars are well understood in this respect.
[quote]But accretion discs move to center, mergers occur in galaxy groups, etc, etc. Why are clusters so stable?[/quote]
Accretion disks behave as they do because of viscous interactions (electromagnetic forces are important). Galaxies are much more diffuse, and their interactions occur over scales similar to their size (with the greatest part of the disruption occurring in the tenuous outer parts, not the cores). Globular clusters are very compact and located far from their parent galaxies with respect to their sizes. So they are not strongly influenced by tidal forces. They simply aren't exposed to much in the way of external perturbations. So most persist until they evaporate. Some, however, must be disrupted by tidal forces when they orbit too closely to a galaxy, or even come to close to another globular. But those are going to be statistically rare events.
[quote]And to me, 13 billion years is a loooong time.[/quote]
To me, it's "we've only just begun".