APOD: M13: The Great Globular Cluster in... (2012 Jun 14)

[Guest]

At http://asterisk.apod.com/viewtopic.php?f=9&t=25290 I had asked about spinning, and Chris L Peterson replied, closing with "Everything is spinning. In some cases you have groups of things that are held together by other forces, and that prevents them from spinning independently of each other, that's all. Nebulas are spinning as well, although generally too slowly to notice many effects caused by it. Inside a nebula, you have all sorts of turbulent motion and spinning- it is precisely the spinning of local regions that results in the formation of stars."

Well, "turbulent motion" is not spinning; and with all those stars and density, the M13 cluster does not show spinning as a galaxy does, if a galaxy is spinning, as all do not seem to do as some do. Spin is still a mystery to me, and seems absurd in the case of spin rates into hundreds per second. I still don't think that spin is explained by talk about angular momentum, I think it could be a separate form of energy, deserving to be studied more. For instance, is being flat a result or a cause of galaxy rotation, and how do globular clusters show that.

[Chris Peterson]

Well, "turbulent motion" is not spinning;

Actually, it is. When you have turbulent motion in a nebula, you have local regions where the net angular momentum is non-zero. That's spinning, and it's what determines the spin of anything that condenses from that region.

and with all those stars and density, the M13 cluster does not show spinning as a galaxy does, if a galaxy is spinning, as all do not seem to do as some do.

All galaxies have some spin. So do all globular clusters. In the case of globulars, however, the spin velocity is slow with respect to the random orbital motions of the member stars.

Spin is still a mystery to me, and seems absurd in the case of spin rates into hundreds per second. I still don't think that spin is explained by talk about angular momentum, I think it could be a separate form of energy, deserving to be studied more. For instance, is being flat a result or a cause of galaxy rotation, and how do globular clusters show that.

In classical mechanics (which is what we're dealing with here), spin is essentially synonymous with angular momentum. It is extremely well understood, and there's really no possibility of it being something exotic like a new form of energy. There's nothing absurd about bodies with extremely high rotation rates- they are easily explained by basic physics and the conservation of angular momentum.

Spiral galaxies, which are flat, have a significant net angular momentum because their formation mechanism left much of their material in orbits with similar angular momentums. Globular clusters (and elliptical galaxies) have low net angular momentum because their formation mechanisms left much of their material in orbits with random angular momentums. It's as simple as that.

[Skytreker]

. http://www.cita.utoronto.ca/~dubinski/G ... htfall.mov

Great movie! Too bad that it isn't in slightly better quality so that single stars doesn't show like square pixels, but nevertheless this is an awesome simmulation of the star movement inside a globular cluster. And yes the quote in the beginning of the file is exactly what came to my mind, when I saw the picture of M13