Talk:Globular cluster/Archive 1
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Shapely
Harlow Shapley deduced the center of the galaxy was way off in the direction of sagittarius in 1917.
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)
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)
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)
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.
-- Run! 00:20, 17 July 2006 (UTC)
- Isn't bolometric correction the difference between visual and bolometric magnitudes rather than apparent and absolute magnitudes?
- Yes. I changed it to distance modulus instead. — RJH (talk)
- Can we have a citation for the large numbers of globular clusters in elliptical galaxies?
- I added in a reference for M87. There's this reference which states it in more general terms: http://www.sciencemag.org/cgi/content/summary/287/5457/1410 — RJH (talk) 23:01, 11 August 2006 (UTC)
Chaos syndrome 20:28, 2 August 2006 (UTC)
Just give me the Basic's..... To much enfo.... —Preceding unsigned comment added by 66.26.225.11 (talk) 21:46, 15 December 2010 (UTC)
- Just read the lead. Comprehensiveness is one of the requirements for a Featured Article.—RJH (talk) 15:46, 16 December 2010 (UTC)
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)
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)
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
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)
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)
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)
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)
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)
- ^ [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
This article does not mention about Super star clusters. Thanks, CarpD 3/20/07
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]
"Sufficient Mass"
What exactly is meant by "Sufficient Mass" in the third paragraph of the introduction? How much mass is sufficient? Perhaps at least a citation?—Preceding unsigned comment added by 128.196.208.117 (talk • contribs)
- Good question, and I don't know the answer. I glanced through the reference attached to that sentence, but I didn't see anything about a lower bound. I'm also not clear whether that is the result of a mass cut-off or a selection effect. Perhaps it just means sufficiently large not to be mistaken for a globular cluster? Does anybody have some insight?—RJH (talk) 17:40, 7 June 2009 (UTC)
Multiple populations in globular clusters
A growing body of observational evidence proved that *all* the globular clusters are host more than one population of stars. In the article it is stated that this is only the case of omega Centauri and G1. I think it is time to update this information.
Andrea
References:
Anderson, J., Piotto, G., King, I. R., Bedin, L. R., & Guhathakurta, P. 2009, ApJ, 697, L58
Carretta, E., Bragaglia, A., Gratton, R., Lucatello, S., Bellazzini, M., & D'Orazi, V. 2010, arXiv:1002.0002
Gratton, R.G., Sneden, C., Carretta, E. 2004, ARA&A, 42, 385
Lee, J.-W., Kang, Y.-W., Lee, J., & Lee, Y.-W. 2009, Nature, 462, 480
Marino, A. F., Villanova, S., Piotto, G., et al. 2008, A&A, 490, 625
Marino, A. F., Milone, A. P., Piotto, G., et al. 2009, A&A, 505, 1099
Milone, A. P., Bedin, L. R., Piotto, G., & Anderson, J. 2009, A&A, 497, 755
Moretti, A., Piotto, G., Arcidiacono, C., et al. 2009, A&A, 493, 539
Piotto, G., Bedin, L. R., Anderson, J., et al. 2007, ApJ, 661, L53
Piotto, G. 2009, arXiv:0902.1422
Siegel, M. H., Dotter, A., Majewski, S. R., et al. 2007, ApJ, 667, L57
Andrea.jena.bellini (talk) 23:16, 26 February 2010 (UTC)
- Interesting. Perhaps it could just state 'most if not all', since the 'all' would be difficult to prove? Thanks.—RJH (talk) 17:23, 27 February 2010 (UTC)
I located the source of Spectroscopic and photometric evidence of two stellar populations in the Galactic globular cluster NGC 6121 (M 4) see above... CielProfond (talk) 02:33, 28 February 2010 (UTC)
- I made some edits to attempt to resolve the issue, along with performing some updates. Hope it all looks okay. Thanks.—RJH (talk) 18:48, 28 February 2010 (UTC)
Thank you! Now it looks much better. I would also spend some words about the Na/O anticorrelation. Anyway, thanks again. Andrea 05:40, 1 March 2010 (UTC) —Preceding unsigned comment added by Andrea.jena.bellini (talk • contribs)
"A galactic core" or "The galactic core"
The article says: A globular cluster is a spherical collection of stars that orbits a galactic core.
When I click on the link "galactic core" it goes to "galactic center" where the article says:
The Galactic Center is the rotational center of the Milky Way galaxy.
That suggests that the "galactic core" and the "galactic center" are the same, and they are the center of the Milky Way galaxy - in other words, that there is only one galactic core. In this case, the present article should read A globular cluster is a spherical collection of stars that orbits THE galactic core., and not "A galactic core".
I don't know a lot about the subject, so please enlighten me if you do. Wawawemn (talk) 15:50, 28 December 2011 (UTC)
216.70.22.249 (talk) 22:27, 3 April 2012 (UTC)
- Yes, galactic core should have its own article that talks about cores in general, rather than about the Milky Way Galactic Center. (Although we do have active galactic nucleus.) For example, Messier 87 has many more globular clusters than the Milky Way, all of which orbit that galaxy's core. Hence the wording is correct in saying "a galactic core", rather than "the galactic core". Regards, RJH (talk) 23:28, 3 April 2012 (UTC)
Actually the author in 2004 asked for suggestions and I have one: I want an orbital path depicted for any/all globular clusters. I have seen it described as orbiting the galactic core, center, out by the ring shadow about 120,000 to 200,000 light years away, etc. A clear orbital path would clear this up and the article is about globular clusters so not understandable why no orbits? 216.70.22.249 (talk) 22:39, 3 April 2012 (UTC) http://www.aanda.org/index.php?option=com_content&view=article&id=63%3Aaaa-press-release-theft-of-a-million-stars-in-globular-cluster-messier-12-7-february-2006&catid=77%3A2006-press-releases-&Itemid=274&lang=en_GB.utf8%2C+en_GB.UT
- I have seen rosette diagrams for globular cluster orbits. It sounds like a useful addition. Regards, RJH (talk) 23:28, 3 April 2012 (UTC)
N^2 vs N^3 : This article contradicts the N-body simulation page
I noticed that the The N-body simulation page on wikipedia N-body_simulation gives the scaling of the "direct" N-body problem as O(N^2) per timestep.
So do numerous other references.
http://www.scholarpedia.org/article/N-body_simulations#Newtonian_gravity:_methods
This page has O(N^3). Obviously they can't both be right? — Preceding unsigned comment added by Commutator (talk • contribs) 20:54, 26 March 2012 (UTC)
- The N-body simulation entry is not cited, so I am unclear of the source. The entry on this article is directly cited and matches the source. I followed the Benacquista (2002) source to Heggie and Hut (2001), which also lists ~ N3 on p. 27. That paper says that simulations of stellar dynamics are far more challenging than cosmological simulations because of the need to simulate close encounters. That's probably why it scales as O(N3) rather than O(N2). Regards, RJH (talk) 21:24, 26 March 2012 (UTC)
- Thanks for the reply. From that source it seems the extra factor of N arises from a need to model heat transfer between stars in a globular cluster, while an "ordinary" gravitational N-body problem doesn't need that and scales as N^2. Commutator (talk) 22:53, 26 March 2012 (UTC)
Linking of billion in Color-magnitude diagram
In the section Color-magnitude diagram, I would have to disagree with the need to link the word billion to the number. I think it is well-understood by nearly all English speakers that a billion represents the number 10^9. We might want to take it out. --Sbluen (talk) 01:43, 5 July 2013 (UTC)
Radii wrong ??
Quote: "Almost all globular clusters have a half-light radius of less than 10 pc, although there are well-established globular clusters with very large radii (i.e. NGC 2419 (Rh = 18 pc) and Palomar 14 (Rh = 25 pc))"
According to Figure 2.24 of Galaxy Formation & Evolution by Mo, Bosch, White; NGC2419 has the physical properties (radius, luminosity) of an Ultra-Compact Dwarf (UCD) super-globular-cluster; whereas, Palomar 14 has the physical properties of a dim Dwarf Spheroidal (dSph), similar to Willman 1 or Segue 1. 208.53.123.210 (talk) 13:52, 14 January 2014 (UTC)
- on second thought, Palomar 14's position, in the overall parameter-space including Luminosity, Radius (half-light), and also Mass, is allot less unlike common GCs, vs. dSph sub-galaxies. Prima facie, Palomar 14 is a low-mass GC, which "ought" to be a few light-years across, but which has been tidally distorted & distended, stretched to ten times that size, by some kind of comparatively close encounter, with another massive object. The current article does not seem to be wrong, to classify Palomar 14 as a GC (although any implication, that Palomar 14 is a large-and-also-bright-and-massive super-GC, akin to NGC 2419, is "wildly" inaccurate).208.53.123.210 (talk) 10:43, 15 January 2014 (UTC)
More sources needed in Globular_cluster#Radii
I've added a refimprove tag since all the definitions stated in that section (ie: core radius, half-light radius, tidal radius, half-mass radius) are unsourced. Anybody has perhaps a text book to source this? Regards. Gaba (talk) 22:45, 25 March 2014 (UTC)
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Galactocentric distances of globular clusters
I'm going to remove the very very wrong statement: "These globular clusters orbit the Galaxy at radii of 40 kiloparsecs (130,000 light-years) or more." which cites Dauphole et al. (1996). This is a misunderstanding of a somewhat vague statement in that paper. The statement is "They cite the well known fact that the distribution of the observed positions of globular clusters has a gap after the galactocentric distance of 40 kpc." A simple look at the Harris catalog reveals that 60% of known globular clusters are at a galactocentric distance of 8 kpc (distance of the Sun from the Galactic center) or less. In fact, their distribution peaks toward the center and drops sharply outward; I will try to locate a literature reference to this fact and update the information. 81.182.197.34 (talk) 09:28, 3 June 2018 (UTC)
We've got lots of uncited text here, as well as many of the sources being from before 2005. This needs additional citations and an update with newer sources. Hog Farm Talk 02:04, 27 January 2021 (UTC)
Image
I want to add this image here:https://earthsky.org/upl/2016/01/globular-clusters-miky-way.gif: it is from a source made in April of 2020. could we use this? — Preceding unsigned comment added by The great Jay (talk • contribs) 10:39, 2 March 2021 (UTC)
- Not unless it’s been released with a license suitable for Wikipedia, which is very unlikely given the copyright tag. And even if the license is ok, it doesn’t look right: all the globular clusters are in the inner Galaxy. —Alex (Ashill | talk | contribs) 14:33, 2 March 2021 (UTC)
- Oh, alright. The great Jay (talk) 03:01, 3 March 2021 (UTC)
- Found the link to where I found the image. https://earthsky.org/clusters-nebulae-galaxies/m13-finest-globular-cluster-in-northern-skies The great Jay (talk) 05:46, 3 March 2021 (UTC)
- Oh, alright. The great Jay (talk) 03:01, 3 March 2021 (UTC)
Multiple stellar populations image
It would be really great if we could get an image that shows the multiple stellar populations in a globular cluster, particularly showing visually the fact that they're different but not all that different. An image like one of the ones in Figures 4 – 23 of this paper with a suitable license would be great to complement the H-R diagram we have. —Alex (Ashill | talk | contribs) 06:42, 13 June 2021 (UTC)
Citations
Currently working through the citations to ensure they are consistently formatted according to MOS:REFERENCES. Any help would be very welcome! Amitchell125 (talk) 18:16, 25 August 2021 (UTC)
Orbits can now be determined
"the orbit of every Galactic globular cluster is now known [using data from Gaia]" says Characteristic radii of the Milky Way Globular Clusters - Could mention GC orbit determination in an introduction to the Tidal interaction section ? If true, can we confirm radial (line-of-sight) velocity is much better known than distance (which was +/- 10%) ? - Rod57 (talk) 16:42, 20 November 2021 (UTC)
Can we say how the distances to GCs are measured
Can we say how the distances to GCs are measured, and what the uncertainty (eg +/- 10% in 2010) is caused by ? - Rod57 (talk) 00:37, 21 November 2021 (UTC)
- The article discusses that RR Lyrae variables and color-magnitude diagrams are used to measure the distance to a globular cluster. I'm not sure how useful a discussion of the causes of uncertainty would be in this context. Cf. Distance measure and Cosmic distance ladder. Praemonitus (talk) 20:19, 10 July 2022 (UTC)
- It is now becoming practical to determine globular cluster distances by direct parallax observations, for the closer ones at least. See this paper for some results and discussion of the distance accuracies. Lithopsian (talk) 20:26, 10 July 2022 (UTC)