Globular clusters

The non amateur stuff. Hawking, black holes, that sort of thing

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Globular clusters

Post by pete-6 »

I have a bit of a passion for globs, partly as I've recently been spending time photographing some of them. And so I'd be interested to learn a bit more about their dynamics, life cycles and so on. Google hasn't come up with all the answers.

I have found out that most globulars follow a highly elliptical orbit around the Galaxy, like a comet: at the periapsis they will be very close to the galactic centre and tidal forces will disrupt them, likewise when their orbit takes them through the galactic disc. In fact it seems that most globulars won't survive more than a few orbits around their parent galaxy before they fall apart.

Also stars are constantly being ejected from the cluster because of close encounters. They 'lose' many stars this way, it seems.

But I wonder what holds the globular together in the first place. What sort of orbit does each star pursue around the cluster? Do they have a common axis of rotation like a galaxy? If so, why are they - well - globular rather than elliptical, disc, or spiral shaped?

Can anyone take it from here?
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Post by KendalAstronomer »

I'll look into my old undergrad course notes, but a few nuggets should include:

They exist in a halo about the parent Galaxy. This spherical allignment is taken as evidence for dark matter as they exist in and out of the plane of the galactic disk.

They are too small, too slow to form discs with the stars that they have. With not enough DM or gravitational forces between the stars, they end up being irregular, like many galaxies do after an interaction. As globs interact with other stars and objects in the parent galaxy, this also means they can't form really regular shapes over long periods of unperturbed time, I think...

All counter-arguments, further comments welcome...
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Post by joe »

I've got some interesting information somewhere on the subject but can't remember which book! I'll try and dig it out, but points I seem to recall are that all the stars have independent eliptical orbits, probably/obviously around something very massive. It was thought that all the stars in globulars were old, "metal" poor stars and relics of the early part of the formation of the galaxy and while this is true for the Milky Way it isn't necessarily for other galaxies. Observations of globulars in other nearby galaxies show both old and new globulars containing heavier elements. In fact there are a few candidates for globulars in the making as we speak but this is in the Large Magellanic Cloud (I think, don't quote me yet). I believe astronomers think that the Tarantula Nebula will result in a globular cluster. Kendal's notes will be more reliable than my memory.

200mm Newtonian, OMC140, ETX90, 15x70 Binoculars.
gary Byrne
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Globular Clusters

Post by gary Byrne »

I hope this link is of some use. :wink:
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