Talk:Globular cluster

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Contents

[edit] Shapely

Harlow Shapley deduced the center of the galaxy was way off in the direction of sagittarius in 1917.

[edit] Rewrite

I plan a major rewrite of this article, any suggestions or comments? Ato 03:14, 26 Apr 2004 (UTC)

I've been trying to add to it. Probably the page needs to be at least as comprehensive as the SEDS article. I think it needs more information on their distribution, elliptical orbits within the milky way, theories on their formation, current mathematical models on star distribution and motions within globular clusters, comparison with globulars within other galaxies (such as M31), and perhaps more on stellar interactions, collisions and ejections. Thanks. :-) — RJH (talk) 15:31, 26 May 2006 (UTC)

[edit] Not in cores

I've deleted the section on Globular Cluster origins which suggest that they are the cores of other galaxies. I don't think thats correct. Globular clusters are very different from dwarf galaxies: they are much denser, and they have a unique age and metallicity. David s graff 06:09, 20 March 2006 (UTC)

[edit] In or out or both?

The intro states that a globular is "a spherical collection of stars that orbits a galaxy as a satellite." The "Ubiquitousness" section says "there are about 150 currently known globular clusters in the Milky Way." Either the first should read something like "orbits or is part of a galaxy", or the second should read "around"? --Flex 00:44, 15 April 2006 (UTC)

Perhaps it could say instead that the clusters orbit the galactic core? — RJH (talk)

[edit] A few suggestions

  • One section in this article does a lot of descriptive talking about the HR diagram. A picture would definitely be appropriate there, otherwise it may be difficult to visualise.
    • There used to be a useful image in that section, but it got whacked and so I took it out. it was this one, I believe: http://apod.nasa.gov/apod/ap010223.html I've since added a new one that hopefully will suffice.
  • Under "Radii" there're some units which I assume are arcseconds, but to the layman would seem to be inches.
    • Done
  • Under "Metallicity" there's talk of "lines of metallic elements". To the astrophysicist this obviously means spectral lines, but there should be some sort of reference (and a wikilink) to spectra and what they are.
    • I added a link. The reference just above that line also applies to the metal lines, so I replicated it.
  • A wikilink to Tidal force would be appropriate in the Tidal section.
    • Added. Thanks. — RJH (talk) 22:44, 11 August 2006 (UTC)

 -- Run!  00:20, 17 July 2006 (UTC)

  • Isn't bolometric correction the difference between visual and bolometric magnitudes rather than apparent and absolute magnitudes?
  • Can we have a citation for the large numbers of globular clusters in elliptical galaxies?

Chaos syndrome 20:28, 2 August 2006 (UTC)

[edit] Good article on hold

Hi all,

I am happy to promote this article but could someone please verify that this edit is correct? And, if not, ammend the article so it is correct?

Cedars 00:55, 13 August 2006 (UTC)

Yes that is more correct. Thank you. — RJH (talk) 15:21, 13 August 2006 (UTC)

[edit] Globular Rotation?

If globulars are held together by their own centre of gravity - does that mean some, or all of them, will rotate independently of the galactic rotation? Or are they always tidally locked to the galaxy, given their age, and therefore always appear the same from any other position in the galaxy, (ignoring minor parallax shifts).

Perhaps you have a slight misunderstanding about the nature of a globular? A globular cluster isn't a solid body, so it can't become tidally locked. (Although globular clusters can become disrupted and even torn apart by galactic tides.) The individual members of the cluster each follow their own paths, but generally orbit about the mass of the other stars. They move through the cluster repeatedly, interacting with other nearby stars as they move through.
About the best analogy I can come up with is that a globular resembles a swarm of birds or bees. The members each move about individually within the swarm, but the swarm as a whole moves along as a mass in the same direction. — RJH (talk) 20:18, 17 August 2006 (UTC)
I think I was treating the globular macroscopically, but I had realised is wasn't a solid body. But for all intents and purposes, was treating it as such, obviously incorrectly. However, I now realise it can't become tidally locked, but would instead become distorted and disrupted by the gravity of the host galaxy. The main crux of my question was whether or not a globular rotates about its own centre of mass, and you seem to imply that this is the case by stating that the stars "generally orbit about the mass of the other stars". In which case - given the realtively small scale of a globular, can this motion be detected currently, and is it known if all globulars rotate in same direction, and with star velocities proportional to the total mass/size of the globular core? — AndrewG 07:37 18 August 2006
Ah, okay. My understanding is that the orbits of the stars is effectively "randomized" within the relaxation time. So the various stellar orbital planes and angular directions are oriented in every which way, rather than having a preferred orbital direction. After a time interval equal to the relaxation time, a star is likely to have assumed a completely different orbit because of the various deflections that occur while passing through the cluster. — RJH (talk) 22:09, 18 August 2006 (UTC)
RJH, you are right, it is certainly true that a globular cluster has its own net rotation, and this parameter is an important attribute of the cluster [1]. Vegasprof 01:18, 21 January 2007 (UTC)
Do you mean rotation in terms of orbital kinematics about a galaxy's center of mass? That's what your source appears to be discussing. I don't think it means the rotation of a globular cluster around an axis through it's own center of mass. — RJH (talk) 17:17, 23 January 2007 (UTC)

[edit] Globular Cluster Stars are not the same age

Breaking News, http://www.nature.com/news/2006/060821/full/060821-13.html , thanks CarpD 8/27/06

Well the article also pointed out that the multiple star-bursts likely happened within a few million years of each other. So compared to the multi-billion year lifespan of the cluster, that's only a tiny amount. I wouldn't want to throw the baby out with the bath water just yet. :-) — RJH (talk) 14:34, 28 August 2006 (UTC)
Mention of Helium-Rich star where they should not be. http://www.newscientistspace.com/article/mg19125675.800-rogue-hot-stars-discovered-in-boring-clusters.html CarpD 9/6/06
Yes that's interesting. It would make sense that the stellar atmospheres would get recycled to form a few, younger stars. — RJH (talk) 14:46, 11 September 2006 (UTC)

[edit] Approved revision notice on article page

I noticed that the approved revision notice had been removed from this article page. This is fine; the approved revisions process is currently being tested; but it should be known that, at present, it suggests a small, unobtrustive notice be placed on the main article page of articles with approved revisions, so users who wish to trade up-to-dateness for previous review can do so without going to the talk page. If anyone has a disgreement with this, please do bring it up Wikipedia_talk:Approved article revisions, so it can be taken into account as we develop the process. Thanks! JesseW, the juggling janitor 07:14, 14 September 2006 (UTC)

The {{approved revision}} template was removed by Messedrocker for reasons listed as "removing wrong/unnecessary template". It was just restored. — RJH (talk) 18:47, 14 September 2006 (UTC)
FYI, the approved revision is now listed in the article milestone template. Gimmetrow 21:55, 19 February 2007 (UTC)

[edit] Etymology in introduction?

To me, it seems unnecessary to have the etymology of ``globular in the introduction, especially when it means, effectively, ``globule-shaped. It's a word in fairly common usage, and besides, articles with complicated names like autostereogram don't bother with etymology much at all. It seemed to impede the flow for me on first reading • Leon 01:54, 23 September 2006 (UTC)

Ack. And to me it seems that the -ar ending does also have latin roots (globularius), so it is not even more English than the word stem globule either... I'll remove the corresponding part of the sentence. --RolloM 17:28, 23 September 2006 (UTC)
Thanks 69.17.73.214, you were even faster than me... --RolloM 17:31, 23 September 2006 (UTC)--RolloM 17:31, 23 September 2006 (UTC)

[edit] complexity ~ N^3 ?

quote:

> The naive CPU computational "cost" for a simulation increases in proportion to N3,

Is it really N3 ?
I thought it is N2.
Is it all about PP method ?

I reckon it's N2 too. Each of N stars has (N-1) forces on it, so the total number of forces is N(N-1) for each time increment. Stephen B Streater 18:56, 23 September 2006 (UTC)
No, the literature says it scales as N3.[1][2] — RJH (talk) 20:57, 25 October 2006 (UTC)

[edit] Clarification

The heaviest objects in globular clusters are expected to sink to the cluster center due to mass segregation. These will be white dwarfs and neutron stars in an old stellar population like a globular cluster. Heavy usually refers to weight, which is not usually used for objects in space where gravity is variable. Does this mean the densest or the most massive. White dwarfs and neutron stars are not the most massive, so I assume it means the densest, so I'm changing it to that, but feel free to correct it (as per usual) if this is an incorrect assumption. Stephen B Streater 18:26, 23 September 2006 (UTC)

Actually I think that degenerate stars such as white dwarfs and neutron stars were formed at an earlier period in the cluster's history, which implies a more rapid evolution and hence a larger [initial] mass than the remaining main sequence stars. So the statement is likely correct, and is based on mass rather than density. I believe I also saw this noted in one of the references, but I can't find it at the moment. — RJH (talk) 20:48, 25 October 2006 (UTC)
I added a link to mass segregation. Heavier, of course, means more massive. The stub at mass segregation does not explain the phenomenon, but I (or someone else) will put in a theoretical explanation of this phenomenon sometime soon, I hope. Vegasprof 01:26, 21 January 2007 (UTC)
Thanks. — RJH (talk) 17:08, 23 January 2007 (UTC)

[edit] Stellar sorting

An addition was made regaarding evidence from the HST about sorting of stars in a globular cluster by mass. The concept of the concentration of the more massive stars toward the core was already being mentioned in the luminosity section with respect to the more general context of core collapse, so the addition represents a redundancy. Mass and luminosity are tightly linked, so I see no conflict in a merger. This is also a result from a single cluster; one that is considered particularly unique in some respects.

After attempting to combined the text into the luminosity section (and adding an appropriate citation tag), however, I found the text had been reverted. I'd like to reach a consensus on this matter so we don't end up in an edit war. Thanks. — RJH (talk) 20:41, 25 October 2006 (UTC)


  1. ^ [http://www.journals.uchicago.edu/AJ/journal/issues/v116n5/980257/980257.text.html The Spin of M 87 as Measured from the Rotation of its Globular Clusters] M Kissler-Patig, K Gebhardt - The Astronomical Journal, 1998

[edit] Super star cluster

This article does not mention about Super star clusters. Thanks, CarpD 3/20/07

Okay I included a mention. Thanks CarpD. — RJH (talk) 14:17, 21 March 2007 (UTC)

[edit] Globular clusters in Science Fiction

This list could be expanded, but here's a few novels/novellas that are set in globular clusters:

  • In the 1960s science fiction series Perry Rhodan, a globular cluster is the location of Arkon, the home world of the race of Arkonides [3]
  • In Dan Simmon's Hyperion Cantos the Hercules cluster is where Earth was secretly moved to after it was supposedly destroyed [4]
  • In Abdul Ahad's First Ark to Alpha Centauri 2 (2006), the planet Pritibee circling a star in globular cluster M15 is home to a long perished Milky Way civilization, whose remains are found in hibernation by the Earth colonists [5] Sitara12 21:29, 23 August 2007 (UTC)