by Ann » Fri May 10, 2019 3:36 am
BDanielMayfield wrote: ↑Thu May 09, 2019 5:58 pm
Chris Peterson wrote: ↑Thu May 09, 2019 2:20 pm
BDanielMayfield wrote: ↑Thu May 09, 2019 2:13 pm
Conservation of momentum. But really, the centers do tend to tighten up over time as the most massive stars exchange momentum with less massive stars. The net result is that on average massive stars' orbits become smaller while less massive stars can get thrown toward the outside of the cluster.
And over a very long time scale, all the stars get ejected and the cluster evaporates.
I wondered about how long that time scale might be, and came up with this from the Globular Cluster article in wikipedia:
The results of N-body simulations have shown that the stars can follow unusual paths through the cluster, often forming loops and often falling more directly toward the core than would a single star orbiting a central mass. In addition, due to interactions with other stars that result in an increase in velocity, some of the stars gain sufficient energy to escape the cluster. Over long periods of time this will result in a dissipation of the cluster, a process termed evaporation.[83] The typical time scale for the evaporation of a globular cluster is 1010 years.[62]
And yet, our galaxy and others still have GCs like M5 that are still holding it together magnificently after 13 x 10^9 years, already longer that the simulation based estimate. Are there any examples of nearly completely evaporated Globulars?
Bruce
NGC 5053 (left) and M53 (right). Photo: Jonas Grinde.
I really don't know if NGC 5053 has evaporated much at all, or if it was more or less born low-mass, large and distended, but faint globular NGC 5053 and bright globular M53 do make a striking pair. Particularly so since they are not only close to one another in the sky, but they are also at relatively comparable distances from us.
Wikipedia wrote:
NGC 5053 is a relatively low mass cluster with a low core concentration factor of 1.32. It sports a stream of tidal debris to the west with a projected length of 1.7 kpc. This stream may have been created through shock-induced processes.[10] The cluster is located less than 3° from Messier 53 and the two have nearly the same distance modulus, which corresponds to a spatial separation of around 2 kpc. There is a tidal bridge joining M53 to NGC 5053, suggesting the pair may have interacted in the past.
But NGC 5053 may not be a "true" Milky Way globular:
Wikipedia wrote:
The chemical abundances of the stars in NGC 5053 are more similar to those in the dwarf galaxy Sagittarius Dwarf Spheroidal Galaxy than to the Milky Way halo. Along with the kinematics of the globular cluster, this suggests that NGC 5053 may have been stripped from the dwarf galaxy.
Ann
[quote=BDanielMayfield post_id=292097 time=1557424705 user_id=139536]
[quote="Chris Peterson" post_id=292094 time=1557411643 user_id=117706]
[quote=BDanielMayfield post_id=292093 time=1557411220 user_id=139536]
Conservation of momentum. But really, the centers do tend to tighten up over time as the most massive stars exchange momentum with less massive stars. The net result is that on average massive stars' orbits become smaller while less massive stars can get thrown toward the outside of the cluster.
[/quote]
And over a very long time scale, all the stars get ejected and the cluster evaporates.
[/quote]
I wondered about how long that time scale might be, and came up with this from the Globular Cluster article in wikipedia:[quote]The results of N-body simulations have shown that the stars can follow unusual paths through the cluster, often forming loops and often falling more directly toward the core than would a single star orbiting a central mass. In addition, due to interactions with other stars that result in an increase in velocity, some of the stars gain sufficient energy to escape the cluster. Over long periods of time this will result in a dissipation of the cluster, a process termed evaporation.[83] The typical time scale for the evaporation of a globular cluster is 10[sup]10[/sup] years.[62][/quote]
And yet, our galaxy and others still have GCs like M5 that are still holding it together magnificently after 13 x 10^9 years, already longer that the simulation based estimate. Are there any examples of nearly completely evaporated Globulars?
Bruce
[/quote]
[float=left][img2]http://www.grinderphoto.se/pics/Med_6.jpg[/img2][c][size=85]NGC 5053 (left) and M53 (right). Photo: Jonas Grinde.[/size][/c][/float]
I really don't know if NGC 5053 has evaporated much at all, or if it was more or less born low-mass, large and distended, but faint globular NGC 5053 and bright globular M53 do make a striking pair. Particularly so since they are not only close to one another in the sky, but they are also at relatively comparable distances from us.
[quote][url=https://en.wikipedia.org/wiki/NGC_5053]Wikipedia[/url] wrote:
NGC 5053 is a relatively low mass cluster with a low core concentration factor of 1.32. It sports a stream of tidal debris to the west with a projected length of 1.7 kpc. This stream may have been created through shock-induced processes.[10] The cluster is located less than 3° from Messier 53 and the two have nearly the same distance modulus, which corresponds to a spatial separation of around 2 kpc. There is a tidal bridge joining M53 to NGC 5053, suggesting the pair may have interacted in the past.[/quote]
But NGC 5053 may not be a "true" Milky Way globular:
[quote][url=https://en.wikipedia.org/wiki/NGC_5053]Wikipedia[/url] wrote:
The chemical abundances of the stars in NGC 5053 are more similar to those in the dwarf galaxy Sagittarius Dwarf Spheroidal Galaxy than to the Milky Way halo. Along with the kinematics of the globular cluster, this suggests that NGC 5053 may have been stripped from the dwarf galaxy.[/quote]
Ann