Quote:
Originally Posted by Robh
Hi Robert,
It can be difficult to differentiate clusters into open and globular clusters in nearby galaxies such as the LMC and SMC and M33.
Thanks, Rob
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Rob,
I am glad you enjoyed my post.
The "open vs globular" distinction may turn out to be somewhat artificial, with the type of structure existing in each cluster dependent mainly on its total mass.
M33 has been proved to contain some globular star clusters which are much younger than the old globulars that are found in our own Galaxy.
In my view, a certain number of the most massive of the star clusters existing in the LMC (e.g. NGC 1846) are probably best thought of as being recently (relatively recently) formed Globular Star Clusters. A recent paper gave an age of about 2 billion years for NGC 1846......not exactly very young (!!), but
5 or 6 times younger than the canonical "old" globular cluster population that is found in most spiral and elliptical galaxies.
Here is a very interesting study of the star cluster population of the LMC:
http://arxiv.org/pdf/1207.5576v2.pdf
The young and intermediate-age Star Cluster population of the LMC is well populated at very large masses e.g. 10,000 to 100,000 solar mass clusters!!
(note: If anyone needs help understanding "the jargon" in this paper, I can help to decipher it!)
It is thought that
at least the most massive of the
newly-formed and compact Star Clusters that are known to exist in various environments (e.g. within the 'starburst' regions at the centres of spiral galaxies, in galaxy collisions, and in the largest gaseous complexes within the spiral arms of galaxies), with these clusters weighing in at some 100,000 solar masses per cluster, could well evolve into ordinary "old" globular star clusters, given enough time.
However, if NGC 3603, which is
currently structured like a globular cluster, gradually loses an appreciable fraction of its 10,000 solar masses of material due to some of its stars exiting from the cluster, it will probably turn into an ordinary open star cluster....... but its future evolution is not well constrained, as yet.
The formation and time-evolution of the most massive newly-formed star clusters has been an area of strong controversy in the professional literature; I am not sure of the latest results in this area.
The star-formation rate of the Milky Way Galaxy (conventionally expressed in units of "solar masses per annum") is very ordinary compared to the star-formation rate of moderately active Starburst Galaxies like NGC 253 and NGC 1365;
and (in general) the
relative numbers of stars that form at many & various specific values of Star Mass are the same, independent of environment (( technically, this is known as the invariance of the stellar Initial Mass Function (an invariant IMF) ))
Therefore, relatively moderate starburst galaxies, which have some 5 to 15 times the star-formation rate of our own Milky Way Galaxy, will form a whole lot more supermassive OB stars than our own Galaxy forms.......
therefore, while the population of Star Clusters in our own Galaxy is "baseline truth", we cannot extrapolate the properties of these local Clusters to other galaxies.
cheers,
Robert