Is a globular cluster a type of galaxy?

[yeletah]

Hi,

Globular clusters (say M13) are a mass collection of stars

A galaxy is a mass collection of stars

Why is a globular cluster not known as a type of galaxy?

what's the differance?

Steve

[Macavity]

There is some speculation that globular clusters might be the remnant nuclei of (lesser) galaxies captured by our own. This based on star type, implied age etc. I suspect at least some of these objects lie along a sort of continuum...

[Mattscar]

As I understand it, isn't it something to do with the fact that they form as part of / in a host galaxy as they tend to be collections of old stars grouped together by gravity. There are some comparisons between globs and spherical dwarf galaxies, but these tend to form outside of a 'traditional' galaxy independently, whereas globs can be seen as a by-product of a galaxy.

As usual, I'm sure someone clever will be along soon

[michael.h.f.wilkinson]

Some globulars are suspected to be remnants of galaxies that merged with the host galaxy (G1 (Mayal-II) for M31 and Omega Cen for ours are candidates). These two are more massive than regular globulars, and show different chemical compositions which indicate not all stars formed simultaneously, as is thought to be the case with globulars.

[Cath]

I found out the other week that they are now seeing young stars in some clusters so they now believe some clusters have 2nd and even 3rd generation stars being born from the matter of older stars in the cluster.

[michael.h.f.wilkinson]

I found out the other week that they are now seeing young stars in some clusters so they now believe some clusters have 2nd and even 3rd generation stars being born from the matter of older stars in the cluster.

True, and tere are the blue stragglers in most globulars thought to be the result of collisions (but maybe also other processes). G1 and Omega Cen are just usually rich in these young stars.

[umadog]

Globulars and galaxies are of such different size, that they really are very different beasts. There are about a million times more stars an average galaxy than there are in an average globular. In other words, a galaxy is a million times more massive than a globular. That's a lot. For comparison, the Sun is 330,000 times more massive than the Earth. So the difference between galaxies and globulars is another factor of three on top of that. On the other hand, there is such a thing as a dwarf galaxy (http://en.wikipedia.org/wiki/Dwarf_galaxy), but these are very different from globulars.

[yeletah]

Thanks Interesting answers,

Maybe all galaxies have a black hole and globulars do not?

If they are a by product of a galaxy, are they like satelites that have escaped orbit?

I assume all the globular clusters we can see originated from the milky way?

Cheers

[Mattscar]

I think all the globs we can see originated from the Milky Way yes. Andromeda is known to have quite afew, but Iv no idea if us mere mortals can see them (having never looked, I wouldn't really know either way )

[umadog]

Yes, the largest of M31's globulars are visible in amateur telescopes. The prime target is G1:

http://en.wikipedia.org/wiki/Mayall_II

http://deepsky.astroinfo.org/And/g1/index.en.php

http://www.perezmedia.net/beltofvenus/archives/000512.html

All Messier and NGC globs are associated with the Milky Way (i.e. they are gravitationally bound to it). One of the furthest I know of is NGC 2419, which is about 300,000 light years away. http://en.wikipedia.org/wiki/NGC_2419 It's only visible as a smudge in an amateur scope (at least when I've seen it in Mag 5.5 skies it was).

It appears that globular clusters can contain black holes: http://www.space.com/17876-black-holes-star-cluster-discovery.html

[AlexB67]

Thanks for posting that. I never knew that channel existed, something new to add and watch at some point. I've forgotten the name of the person in that video. I believe he is some bigwig in that field no doubt , I do recognise him though, he often appears in the sixty symbols series of videos as well, also an interesting series, though are geared more towards physics. Interesting thread

[Knight of Clear Skies]

As others have said, a typical globular cluster is much smaller than a galaxy and forms inside one. However, observationally there can be little difference between a large globular cluster and the core of a dwarf galaxy. This is a common problem in taxonomy: nature often presents a continuum of objects rather than ones which fit neatly into the categories we have designed.

Most globular clusters are very old, because massive concentrations of star-forming material were much more common in the early universe. Smaller open clusters, such as the Pleiades, dissipate over a few million years: as they consist of fewer stars, they are less strongly held together by gravity.

[yeletah]

Thanks, new knowledge,good video.

Am I correct in thinking M13 is older than M2 as it has a greater number of stars?

I.e M13 has regenerated more stars within itself and therefore has become a larger globular cluster than M2 due to a longer expanse of time,therefore older?

[Knight of Clear Skies]

M2 (13 billion years old) is thought to be older than M13 (11.5 billion years). The basic dating method is to look for the stars which are moving off the main sequence and evolving into red giants. For example, a star with the mass of the sun will remain on the main sequence for about ten billion years, so if the stars of this mass are making the transition then the cluster must be about ten billion years old. The underlying assumption here is that all the constituent stars formed together in one nebula, which is true of many but not all clusters.

Hope that makes things a bit more clear, it took me a while and a lot of reading to get my head around all this.

[Macavity]

It would certainly be an interesting visual environment for an (unlikely) inhabitant. A bright star, every light year or so - Never a dark night? The parent galaxy dominating a large part of the sky, and nothing but DSO's in other (more distant) directions? Something like: http://astrobob.area...obular-cluster/ maybe...

[LukeSkywatcher]

Ive never really thought about exactly what globular clusters are or how they come to be. Infant galaxies/solar systems?, leftovers of galaxy collisions?, Nebulae giving birth to stars but without the gas and dust (nebulosity)?

I really dont know. They look great though.

[Friedberg]

Exploded "Death Stars"....... May the force be with you!

[bomberbaz]

Fascinating subject with some great input. I will go thoigh the links once i am back on pc.