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What is the center of a globular clusters made of?

  1. Feb 12, 2015 #1
    what's the center of a globular cluster , is it a star or can it be a black hole ? how are they formed and bound to gravitational pull of the milky way
     
  2. jcsd
  3. Feb 12, 2015 #2

    DEvens

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  4. Feb 12, 2015 #3

    mfb

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    Mainly empty space.
    There can be a black hole, but that is not necessary. Individual stars can stay close to the center for a while, but they are not massive enough to avoid perturbations from other stars which move them around over time.
     
  5. Feb 12, 2015 #4

    Garth

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    One question of course is that of the internal orbital mechanics; once formed how do globular clusters remain so tightly bound for nearly the age of the universe? Open clusters have lifetimes < 100Myrs. or so.
    Globular Cluster
    So what keeps the globular cluster so tightly bound, for example, are there BH's at the centre?
    Garth
     
    Last edited: Feb 12, 2015
  6. Feb 12, 2015 #5
    Globular clusters are beautiful and weird. There are many mind boggling questions associated with them. This was the best text answering many of those questions -including yours- I have read so far. "A Thousand Blazing Suns: The Inner Life of Globular Clusters http://www.astrosociety.org/pubs/mercury/9904/murphy.html [Broken]"
     
    Last edited by a moderator: May 7, 2017
  7. Feb 12, 2015 #6

    davenn

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    The first obvious choice would be mutual gravitational attraction between the members of the globular cluster
    Since there are vastly many more stars in a CG than in an open cluster. The gravitational attraction would be more substantial
    As mfb said, there may be a BH at the core of some of them, but it wouldn't be necessary to keep the GC compact.

    Open clusters, on the other hand, are generally likely to be less than a couple of 100 stars, with many much less than that, a few dozen or so.
    They are also spread out over a larger area meaning mutual gravitational attraction is going to be lower and this would allow for
    members of the OC to drift apart over time.

    Dave
     
  8. Feb 12, 2015 #7

    davenn

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    interesting looking article .... will get a chance to read it soon

    thanks
    Dave
     
    Last edited by a moderator: May 7, 2017
  9. Feb 13, 2015 #8

    Garth

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    Hi davenn!

    Yes, of course, however the question arises of the stability of the member stars' orbits over ~ 10Gyrs. With perturbations of many nearby neighbours mergers between members and ejections from the globular system must be common, far more so than in the galaxy at large.

    Obviously they have survived and are stable over such long periods but mathematically the stability question is an interesting one.

    Garth
     
    Last edited: Feb 13, 2015
  10. Feb 13, 2015 #9

    marcus

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    Some nice stuff in that wikipedium! It pointed to something about intermediate-mass BH,
    http://hubblesite.org/newscenter/archive/releases/2002/18/text/
    which in turn pointed to:
    http://arxiv.org/abs/astro-ph/0209314
    http://arxiv.org/abs/astro-ph/0209315

    http://arxiv.org/abs/astro-ph/0508251
    http://arxiv.org/abs/astro-ph/0209313
     
  11. Feb 13, 2015 #10
    Is it possible, that GCs are the tidally stripped down cores, of previously larger and more distended objects?

    Can individual GCs be resolved, at cosmological distances? If so, then are they larger?

    Gravity causes less massive objects to be scattered outwards, whilst more massive members sink towards the center... Less massive members farther from GC center might be easier to strip off
     
  12. Feb 13, 2015 #11

    davenn

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    yes, tho I haven't found any images or info on if the individual stars in the GC's can be resolved

    There are many images showing GC's around other galaxies
     
  13. Feb 14, 2015 #12
    T
    Those would be very important observations... If so then GCs are largely intact ancient relics
     
  14. Feb 16, 2015 #13
  15. Feb 16, 2015 #14
  16. Feb 16, 2015 #15

    marcus

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    May I conjecture? Imagine that a swarm of globular clusters forms first, before there IS a galaxy:smile:
    a swarm not only of globular clusters as we know them, but of smaller collections of various sorts: proto-galaxies, dwarf galaxies, blobs of stars and gas, etc.
    then there is a kind of "bottom-up" coalescence rather than "top down".

    These globular clusters, if I remember correctly, do not orbit AROUND our galaxy, they typically orbit through, they "yo-yo" through the galactic plane
    When dwarf galaxies do that, they lose stars as they pass through. They get slightly disrupted. So they gradually contribute stars to the main galaxy. Outliers get shaved off.

    So I am imagining that the globulars do not have to "come into" orbit or " become satellites" of a galaxy. It is the main galaxy which "becomes" in their midst. Out of a the swarm of smaller clots and curdles. With the help of the dark matter halo. they are prior.

    Perhaps the globulars are the SURVIVORS of this process and look the way they do because, like pebbles, they have been worn smooth by many passes through the plane of
    collective rotation.

    BTW there is a Wippy Kidium on "Galaxy formation" . I don't think structure formation and galaxy formation in particular is a completely solved problem. It probably doesn't hurt to imagine various alternatives.
     
  17. Feb 17, 2015 #16
    A globular cluster is a group of stars bound together by gravitational effects which only increases as you approach the center and the number of stars per a given area increases too.
     
  18. Feb 17, 2015 #17

    davenn

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    yes, that's correct as can be seen by the images posted up the page :smile:

    Would be an interesting place to be on a habitable planet around one of those stars

    Dave
     
  19. Feb 17, 2015 #18

    mfb

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    The star densities there are not good for the long-term stability of planetary orbits.

    But it could give an amazing view of the milky way.
     
  20. Feb 17, 2015 #19

    davenn

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    Yup I would suspect that

    Uh huh, specially if in one well above the galactic plane :smile:

    That made me think of the view of the MW from one of the Magellanic Clouds, would also be an awesome sight

    Dave
     
  21. Feb 19, 2015 #20

    wabbit

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    You'd need to be in its remote suburbs though, otherwise I suspect the sky would be so bright from all the nearby stars surrounding you that you wouldn't see the milky way at all. Which would be quite a sight in its own right...
     
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