Talk:Star

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"Atmosphere" correction

At the end of the "Main sequence" subsection, the word "atmospheres" incorrectly points to the term "Atmosphere (unit)" instead of the term "Stellar atmosphere". Please correct and then remove this comment. — Preceding unsigned comment added by 109.100.69.106 (talk) 18:22, 1 October 2012 (UTC)

Done. Thanks. —Alex (ASHill | talk | contribs) 00:54, 2 October 2012 (UTC)

Largest stellar mass

Sorry if I started this section incorrectly, I'm new at this, so feel free to move/fix/delete as needed.

Anyway, I found this at the end of the section on stellar mass: "However, a star named R136a1 in the RMC 136a star cluster has been measured at 265 solar masses, putting this limit into question."

I was reading somewhere recently that this actually presents a couple of possibilities--first that the Eddington Limit might need to be updated, and second that the star is actually two stars of much lower than Eddington Limit mass. I can't find the reference, so maybe that is not true, but I just thought I'd point it out.

Also, it seems to me that the Eddington Limit tells us that stars above a certain mass will be dominated by the radiation pressure vs the gravity holding them together, and thus will blow apart. Looking at the Wikipedia article on this star, it appears that it is doing exactly as predicted for a star above this limit, it is shedding mass very quickly. Doesn't this mean that the theory is supported, rather than the limit has come into question? I mean, just because a star is above the theoretical limit for the upper mass of stars (which is really just the limit to how big a star can be before radiative pressure starts shedding its mass), that doesn't mean the star can't exist, it just means that above that limit, if a star does exist, it will be very busy blowing its mass into space. Yes? No?

Perhaps a better wording would be to talk about how stars above this mass are rare because of the dominance of radiative pressure (they die very young), and that when a star above this mass is found (such as R136a1, with 265 solar masses) that star should be in the process of blowing itself apart from the moment it is born. Again, I'm not an expert or professional astronomer, and perhaps this is still too new to be considered 'fact,' but I love to point stuff like this out in case I can learn something from it.  :) Turboguppy (talk) 18:16, 23 September 2011 (UTC)

If I recall the issue correctly, I think the concern is not whether a cloud with that much mass can form and start to collapse into a protostar, but how does it become a main sequence star without blowing off the extra mass in the process? I know that one way to do it is to have a star with no metallicity, as is the case with the conjectured population III stars. The ESO article being used as the source suggests another method: the merger of two smaller, but still massive stars. You give the third option yourself: that it is actually a massive binary. As for the wording itself, well I guess that's just a common process in science; exceptions that test the consensus. Regards, RJH (talk) 19:19, 23 September 2011 (UTC)

Thanks, I think that clears up the confusion for me--it will be interesting to see what comes of it. Thanks! Turboguppy (talk) 03:09, 28 September 2011 (UTC)

Main Sequence Stars

I have noticed that in the article it says that Main Sequence Stars are also called dwarf stars, which is incorrect as only some stars in the main sequence are dwarf stars. For example, a Blue Giant is a Main Sequence Star.—Preceding unsigned comment added by 162.115.172.120 (talk • contribs)

I believe that in this context the term "dwarf star" is used to describe a star that has a "normal" size for its mass. So a Blue Giant is also a dwarf star. It's an unfortunate term.—RJH (talk) 22:20, 6 April 2008 (UTC)

Maybe it could just be worded differently somehow, because I could also see confusion arising when dealing with a "white dwarf" star, where it could be perceived as part of the Main Sequence when it really isn't. —Preceding unsigned comment added by 162.115.172.120 (talk) 00:53, 11 April 2008 (UTC)

It doen't make any sense to me either, but any star in the main sequence is technically considered a dwarf. Why there are white dwarfs and black dwarfs too is incomprehensible to me. Sorry, but that's how it is. J.delanoy^gabs_adds 01:01, 11 April 2008 (UTC)

See Stellar Classification#Yerkes spectral classification for the description of the so-called "luminosity classes". "Dwarf" means a star of luminosity class V (five), also known as a main sequence star. "White dwarf" is something else entirely, just to keep you confused. Like many terms in astronomy, it's a collection of historical artifacts because these things were all named before anyone knew what was going on physically, and the arcane names have stuck around. It's a shame, but that's the way the field is. "Black dwarf" is an uncommonly used term, largely because of the possibility for confusion with white dwarfs and dwarf stars. I'll try to clean up the language in this article to clarify things a bit, but it comes down to confusing, poorly chosen nomenclature that we all use. ASHill (talk) 05:01, 11 April 2008 (UTC)

I changed dwarf star, which was a redirect to main sequence, to a page explaining the various uses of the term dwarf in the context of stars. ASHill (talk) 05:33, 11 April 2008 (UTC)

If the term causes confusion, then perhaps black dwarf ought to be merged with the white dwarf article.—RJH (talk) 14:40, 11 April 2008 (UTC)

I don't think that's necessary; even though the term is not one I've often heard or ever used myself, the black dwarf page is very clear about what it means and it does have a somewhat distinct meaning from white dwarf. ASHill (talk) 15:25, 11 April 2008 (UTC)

My apologies if this is the wrong place to ask a question, but this paragraph has me perplexed and curious: "The duration that a star spends on the main sequence depends primarily on the amount of fuel it has to burn and the rate at which it burns that fuel. In other words, its initial mass and its luminosity. For the Sun, this is estimated to be about [10 the power of 10] years."

100 Billion years, if my math is correct. A 10 with 10 zeros attatched. Given the age of the universe, this comes as a bit of a surprise. Perhaps a reference? —Preceding unsigned comment added by Luciusmichael (talk • contribs) 03:07, 7 July 2008 (UTC)

10 to the power of 10 is actually a 1 with 10 zeroes - 10 billion years in other words. This is the correct figure for our Sun. But thanks for checking - sometimes mistakes make it in and its good to keep your eyes open. PhySusie (talk) 03:15, 7 July 2008 (UTC)

For a reference, see: Main sequence#Lifetime —RJH (talk) 15:00, 7 July 2008 (UTC)

I totaly agree that they shouldn't put the fate of the Earth in the article. Since we still don't have a 100% picture on the Earth to Sun relationship. — Preceding unsigned comment added by Karicats7 (talk • contribs) 20:50, 14 March 2012 (UTC)

Can stars have rings?

Are there any stars that have rings? YouthoNation (talk) 18:15, 30 September 2008 (UTC)

Yes: Debris disk—RJH

(talk) 19:09, 30 September 2008 (UTC)

Sort of, but only protostars or possibly brown dwarfs can have anything similar to a planet's ring. Skyintheeye (talk) 21:29, 9 February 2010 (UTC)

Samples of stars which have ring? Newone (talk) 03:03, 12 October 2010 (UTC)

Well, one might consider a debris disk a ring, albeit probably not as flat as Saturn's rings. There's also the protoplanetary disk, which is comparable.—RJH (talk) 14:53, 12 October 2010 (UTC)

The solar system is made out of the sun, and all of the debri around it. The debri around the star becomes planets and asteroids. So, in essence yes, a young solar system with a star in it has 'rings'. Karicats7 (talk) 21:01, 14 March 2012 (UTC) (talk)

I suggest the asteroid belt in our own solar system is a 'ring'. Jokem (talk) 21:09, 20 July 2012 (UTC)

Definition

"An astronomical object is defined as a star if it emits more heat, light and radiation than it absorbs." Does anyone know where this definition comes from and its vailidity? By this definition Jupiter, apparently, is a star, not a planet. __meco (talk) 10:24, 28 September 2011 (UTC)

This wording looks to be invalid and has some redundancy; both heat and light are radiation. I have no idea where it comes from. You could perhaps define a star in terms of whether it acquires sufficient mass to perform thermonuclear fusion of protons (not deuterium) to form helium at some point during its lifetime. But there are conjectured to be dark matter stars that could throw that definition out the window. Still, you'd need a definition that excludes deuterium-fusing brown dwarfs. Regards, RJH (talk) 16:16, 28 September 2011 (UTC)

I appreciate your take on it. It wasn't much of a reliable source, so I just figured I'd throw it out to see if anybody could somehow elaborate on it, which you did. __meco (talk) 08:22, 2 October 2011 (UTC)

Edit request from 94.66.78.71, 30 September 2011

Star, derives from a combination of Greek "αστήρ" (endless) with "άστερεον" (non-fixed) and "αστράπτον" (flashy)

94.66.78.71 (talk) 21:52, 30 September 2011 (UTC)

We'll need a reliable citation for this. It's only partly confirmed here:

Halsey, Charles Storrs (1882), An etymology of Latin and Greek, p. 80

The online etymology dictionary shows it as coming from aster, per the first above:

Harper, Douglas (2010), "star (n.)", Online Etymology Dictionary, retrieved 2011-09-30

Regards, RJH (talk) 21:54, 30 September 2011 (UTC)

Edit request from , 1 November 2011

{{edit semi-protected}} Please, change

Chugainov, P. F. (1971). "On the Cause of Periodic Light Variations of Some Red Dwarf Stars". Information Bulletin on Variable Stars 520: 1–3. Bibcode 1977A&A....61..809M to

Chugainov, P. F. (1971). "On the Cause of Periodic Light Variations of Some Red Dwarf Stars". Information Bulletin on Variable Stars 520: 1–3. Bibcode 1971IBVS..520....1C

because the Bibcode is wrong.

With best regards, Andras Holl (IBVS technical editor)

Andrasholl (talk) 10:22, 1 November 2011 (UTC)

Changed, thank you. Materialscientist (talk) 10:29, 1 November 2011 (UTC)

Dead links

So many wrong links! Newone (talk) 05:02, 11 April 2012 (UTC)

Fixed. This is quite "normal" for a large article which has not been overhauled for deadlinks for some time. Materialscientist (talk) 05:22, 11 April 2012 (UTC)

Red riant mass Discrepancy

Solar mass required for a star to become a Red giant according to various articles:

• Red Giant - 0.35
• Star - 0.4
• Stellar Evolution - 0.5

The same discrepancies can be found a mass limit for a star to fuse helium in various articles.

• Horizontal branch - 0.26 (presumably a mass for a star to become red giant)
• Star - 0.4 (not directly said)
• Helium flash - "about 0.5"
• Stellar Evolution - 0.5

--Artman40 (talk) 01:23, 17 June 2012 (UTC)

They should all probably be based on the lower bound for fusing helium, so around 0.5. (D'oh... I was mistaken. The lower bound would probably be a hydrogen-burning shell stage with an inert helium core, rather than helium fusing.) We need to find a definitive reference that will serve on all of the articles. Also, I'm not sure if there is significant variation caused by metallicity. Regards, RJH (talk) 22:42, 21 June 2012 (UTC)

These numbers largely reflect the uncertainty in this number; really, the text should reflect that uncertainty. It's unconstrained by observation anyway, since the age of a 0.5 solar mass star is longer than the current age of the Universe. —Alex (ASHill | talk | contribs) 23:13, 21 June 2012 (UTC)

If it is of any help, the following source estimates the lower limit at around 0.25, with stars needing 0.5 to reach the tip of the RGB:

Laughlin, Gregory; Bodenheimer, Peter; Adams, Fred C. (1997), "The End of the Main Sequence", Astrophysical Journal, 482: 420, Bibcode:1997ApJ...482..420L, doi:10.1086/304125. {{citation}}: Unknown parameter |month= ignored (help)

I'm not sure if there is a more definitive source available, but this seems pretty decent. Shrug. Regards, RJH (talk) 03:41, 22 June 2012 (UTC)

Thanks for the ref. There's a conference proceeding version that's a little easier to read: 2004RMxAC..22...46A. My summary for this purpose is that the maximum luminosity of stars increases for stars in the 0.16 to 0.25 solar mass range; there doesn't seem to be a sharp transition. All that said, there are no observable tests of this aspect of the model. I'll try to incorporate this into an article where appropriate, if someone doesn't beat me to it.

Re what determines the lower bound: it's the fully convective interior. Fully convective interior means no red giant phase (because convection mixes mass from through the star, so the star can fuse nearly all of the hydrogen in the star, not just the hydrogen in the core); radiative interior means red giant. I haven't (yet) looked at the articles to see if this is said well; if it isn't, it should be. —Alex (ASHill | talk | contribs) 10:01, 22 June 2012 (UTC)

Adams, F. C.; Graves, G. J. M.; Laughlin, G. (2004), García-Segura, G.; Tenorio-Tagle, G.; Franco, J.; Yorke, H. W. (eds.), "Gravitational Collapse: From Massive Stars to Planets. / First Astrophysics meeting of the Observatorio Astronomico Nacional. / A meeting to celebrate Peter Bodenheimer for his outstanding contributions to Astrophysics", Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias), 22: 46–49, Bibcode:2004RMxAC..22...46A. {{citation}}: |contribution= ignored (help); Unknown parameter |month= ignored (help)

Perhaps I'm mistaken, but I got the impression from the first article that stars with 0.25 solar masses may develop radiative core regions later in their lives, even though they are normally fully convective. (Perhaps from the higher abundance of helium?) Interesting if true. Regards, RJH (talk) 14:44, 22 June 2012 (UTC)

editrequest

After the phrase "putting this into question.[ref]" please add the following sentence into the same paragraph as its new last sentence:

A study have determined that stars larger than 150 solar masses in R136 were created through the collision and merger of massive stars in close binary systems, providing a way to sidestep the 150 solar mass limit.

-- 76.65.128.252 (talk) 07:48, 24 August 2012 (UTC)

Done. Thank you, RJH (talk) 14:20, 24 August 2012 (UTC)

Lead image

Which version? I prefer the larger version since it gives more context. If there is an awkward strip of text beneath one or the other when you see it in the article, that formatting is may due to the width of your browser window rather than being the "fault" of either image.

Smaller

Larger

Does anyone else have a preference? I prefer the larger version. Pine^✉ 07:40, 6 October 2012 (UTC)

I prefer the smaller one because the larger one seems a bit too tall, and ends up pushing the text into narrower area which doesn't look good to me, not to mention it does leave a strip of text underneath for most modern screen resolutions. If you could somehow find an intermediate between those two maybe that would be better. Cadiomals (talk) 14:28, 6 October 2012 (UTC)

Age Does Not Specify Type of Billion

The article notes the age of stars as "1 to 10 billion years", but does not specify if it is a US billion (thousand million) or a European billion (million million). As this is a significant difference, it would be very helpful if the article listed the age as a fully-written number in order to more clearly specify units. I'd edit it myself, but the citations don't seem to clarify, either.