Quote:
Originally Posted by Paddy
For GCs in the Milky Way isn't there also a distinction based on the age of the constituent stars? I know this doesn't fit in the Magellanic Clouds.
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Hello Paddy,
I once looked into the idea of massive and centrally-concentrated clusters of various ages , and whether or not these "various ages" globular star clusters exist in different types of galaxies;
It appears that most non-dwarf spiral galaxies of type Sbc or Sc can form at least modest numbers of new globular clusters, with time........
for instance, in the Milky Way;
NGC 3603, Westerlund 1, and the Arches Cluster, have formed recently.
( NGC 3603 may be a little too small for a globular, especially if it eventually loses some of its stars, as it is currently of the order of 10,000 solar masses.)
There were some initial studies of M83 showing that M83 has recently formed good numbers of
100,000 solar mass, massive & compact, star clusters in the numerous extremely large star-forming complexes that exist in its two main spiral arms; but oddly, these low-resolution observations were never followed up with high-resolution (0.05 arcsec or better) Hubble Space Telescope observations of these clusters ( at least this was the case when I last checked the literature some two years ago!)
Generally, if there exists a Big Enough and Energetic Enough star-forming complex in any galaxy that exists anywhere (
or anywhen) in the universe, meaning that there is a sufficent mass of cold molecular gas in the complex and that the amount of energy supplied to begin gas contraction & star formation (energy supplied by gravity, supernovae, stellar winds, violent supersonic turbulence, etc.) is high enough, there is a chance that a massive & compact Young Cluster will form that is essentially indistinguishable from a young globular cluster.
In other cases in the universe, if you give the interstellar medium a big enough "whack" with a shock wave, such as in a collision between two galaxies, new globular clusters can and do form (e.g. in NGC 4038/9 and NGC 3256)
The canonical "old" globulars are a distinct population, or more properly
populations (in the plural), of clusters;
these "old" globulars exist in just about every non-dwarf galaxy in the universe.
However, I caution that "old" can mean different things depending on the particular galaxy; usually, astronomers mean between 8 and 12 billion years old when thay talk of "old" objects.
Some galaxies, such as NGC 1316, contain some
intermediate-age globulars which are only 3-6 billion years old, but these globular star clusters are already looking
a lot like your typical globular, because they have already lost all of their young and luminous stars.
cheers, robert
As a matter of interest checked my observing logs for NGC 7006 and found this - "Very remote GC. Easy to see in 4.5-inch. Dim, very small, centrally brightened glow. Seen 5 September 2007." That was at 43x.
