Talk:Red dwarf

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Metallicity[edit]

It seems to me that if we have not observed any red dwarf stars with zero metal content, then we have indeed observed red dwarf stars that have moved off the main sequence and we are still left with the puzzle of determining the precise age of the universe. About all we can say for certain is that the universe should be much older than the estimates that are popular at the moment.

Red dwarf stars are so common that we haven't even bothered to study most of the ones we've discovered. If we haven't discovered a red dwarf of Population III, it's probably because we haven't looked hard enough. If low-mass stars formed during that age of the Universe, then both red and orange dwarfs with no metals should exist. No star of less than 80 percent of the mass of the Sun has evolved off the main sequence yet. user:Jsc1973

The reason I bring this up is because I cannot imagine how you find a red dwarf that has gone cold. It seems unlikely that they would become white dwarfs harboring degenerate matter. This is a case of an absence of something indicating a condition we have failed to properly conisider.

Giant dwarfs[edit]

I disagree with this statement:

Red giants, at least as expected with Sun-like stars, occur before the initiation of helium fusion, with shell hydrogen fusion. Although it might take more-then-the-current-age-of-the-Universe for red dwarfs to reach the point of having an inert helium core, I could imagine this state of affairs, at least with the bigger end of red dwarfs. Does anyone have any better information? Joffan 19:02, 16 September 2005 (UTC)

IIRC, red dwarves have convection cells going all the way down to the core, so there is no shell hydrogen fusion. One of the reasons they live so long is that most of the hydrogen in them reaches the core at some point, so the core is never "inert" until they die. Linguofreak 04:42, 10 April 2006 (UTC)


At the begining of the Main Sequence red dwarfs are fully convective. As a red dwarf ages the hydrogen to helium ratio decreases throughout the star. This forces the temperature of the core up to maintain the rate of fusion. At some point this causes a radiative shell to develop between a convective core and a convective exterior. The hydrogen outside the core is no longer available for fusion and the evolution proceeds rapidly. What happens next depends upon mass.

For masses greater than about 0.25 to 0.20 solar masses, fusion in the core proceeds until the hydrogen is exhausted. The core contracts, heats up and the star turns off the main sequence. It becomes a red giant under-going hydrogen shell burning around an inert helium core. However the star does not reach a core temperatures sufficient to undergo the helium flash, fusion slows and ultimately ends.
For lower masses the core of the star is already partially supported by degenerate electron pressure. As a result of this, there is a limit to the amount the core can contract to maintain the fusion rate. So that as hydrogen is exhausted in the core fusion throughout the star slows and dies. The low mass M-dwarf never becomes a red giant.

Disclaimer, much of what I have said above occurs on timescales greater than the age of the Universe, so is completely untestable. Thus this is more speculation than rigorous science. --Ealdian 14:26, 17 August 2006 (UTC)

Population III stars.[edit]

Stars of extremely high mass that burned out quickly, by cosmological standards, and thereby created all the metals needed for the current crop of Population II and Population I stars. Shouldn't this have left us with a very high number of neutron stars, magnetars, and black holes? Wouldn't the consequences of having a large number of such objects around be rather serious?

Here, I am not criticizing Wikipedia as this seems to be an accurate exposition of current theory. Nevertheless, I do have serious misgivings about the theory. Granted, Astronomers, Astrophysicists, and Comologists need a theory to work with and from, but they seem terribly cocksure at times.

Quoting the article on Pop III stars here, because I cannot get the talk tab to work on that article:

"If these stars were able to form properly, their lifespan would be extremely short, certainly less than one million years. As they can no longer form today, viewing one would require us to look to the very edges of the observable universe. (Since the time it takes light to reach Earth from great distances is extremely long, it is possile to see "back in time" by looking farther away.) Seeing this distance while still being able to resolve a star could prove difficult even for the James Webb Space Telescope."

If the theory concerning these putative stars is in any way correct, then JWST should be able to view entire galaxies of such stars, yes? The spectra of nearly all the stars should all be very nearly the same, depending upon the age of the putative galaxies of Pop III stars. In fact I would expect the spectra of such young galaxies to fall into "bins" according to their ages. A galaxy only one million years old should be easily distinguishable from one that is slightly older than one million years and so on until all the Pop III stars have had time to burn out. Metalicity galaxy wide should increase with age in almost stair-step fashion.

It amazes me, by the way, that something around one percent or less of elements heavier than helium can have such profound effects on stellar size. Current counts suggest that the overwhelming majority of Pop II and Pop I stars are K to M class dwarfs. Why the anticipated paucity of such stars in Pop III? Simply because we have not found any such stars that have turned off the main sequence?

Personally, I think it is more likely that we have not found them because they are dim and we have not devoted enough instrument time to look for them. But, then again, perhaps the black holes gobbled them up.

70.116.68.198 06:56, 1 January 2006 (UTC)Don Granberry.

Maybe red dwarfs are population llll stars(Population lll stars with carbon) —Preceding unsigned comment added by Alexrybak (talkcontribs) 17:16, 22 May 2011 (UTC)

More on Population III Stars[edit]

Here is a very useful link:

http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v540n1/50350/50350.html

Somewhere along the way, their simulation runs must have butted heads with Xeno of Elea. They assume the existence of "dark matter" and a considerably less than homogenous cloud structure in the "early universe."

There is no suggestion that any non-linear, self-iterative processes were considered. Such large clouds of gasses would necessarily be affected by such processes. Quoting the above linked article:

"What will be the fate of the collapsing core? Within the core the number densities increase from 105 to 108 cm-3. For densities ≳108 cm-3, however, three-body formation of H2 will become the dominant formation mechanism, transforming all hydrogen into its molecular form (Palla et al. 1983). Our chemical reaction network does not include this reaction, and the solution cannot be correct at r ≲ 0.1 pc. The most interesting effect of the three-body reaction is that it will increase the cooling rate by a factor of ∼103, leading to a further dramatic density enhancement within the core. This will decrease the dynamical timescales to ≪100 yr, effectively decoupling the evolution of the fragment from the evolution of its host primordial molecular cloud. Therefore, it is a firm conclusion that only the gas within these cores can participate in Population III star formation."

The model used relies non-local thermodynamic equilibrium and this can be problematic.

http://www.physics.usyd.edu.au/astron/iau189/toc-posters.ps


Also, the one description of the nucleosynthesis process in Population III stars that I could access assumes that the stars are not rotating.

http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v567n1/54373/54373.text.html?erFrom=-7768877433592011253Guest


The upshot is that we appear to be placing a wee bit too much faith in a computing model limited by computing resources, particularly when it is claimed that only very large stars (30 to 1000 solar masses) were made during this period of cosmological history and that none of those stars were in rotation.

While this IS a good working theory on which to foot further investigations, the investigators seem to be entirely too eager to comply with pre-conceived notions. In court they would be accused of "assuming facts not in evidence." Rather than being an effort to discover the nature of stars that formed during the early periods of the universe, assuming the universe had an "early period", this seems to be an attempt to shore up a problem ridden model of the universe.

The current cosmological model may one day be shown to be correct, but dogmatic adherence to it prior to such a demonstration strikes me as being a very poor procedure. While a sincere search for very old red dwarfs or K stars of Population III origin would be arduous, it should nevertheless be carried out.

70.116.68.198 17:29, 1 January 2006 (UTC)Don Granberry

Carbon[edit]

Do Red Dwarfs have any carbon within them? Zachorious 05:09, 31 July 2006 (UTC)

All observed red dwarfs contain carbon. Carbon is in the top 5 most abundant elements in the Universe. It is likely that the only red dwarfs which contain no carbon belong to Population III. If such stars still exist they are may have accreated material from the interstellar medium or a companion star and so contain at least a tiny amount of carbon. You may be interested in the extremely iron deficient star HE 1327-2326, which has an iron to hydrogen ratio of 1/250000 of the solar value.

Carbon?Aha!Carbon in outer layers,NOT IN THE CORE! —Preceding unsigned comment added by Alexrybak (talkcontribs) 17:08, 22 May 2011 (UTC)

Nucleosynthysis[edit]

This statement does not seem right to me

I assume 'fuses hydrogen in the presence of metals' refers to the carbon-nitrogen-oxygen (CNO) cycle in which fusion is catalysed by C,N and O. However, the CNO cycle does not become efficient until temperatures in excess of around 16 million Kelvin are reached. On the Main Sequence, such temperatures are only reached in stars of greater than about 1 solar mass. For low mass stars (and the Sun) the main fusion reactions which occur are those of the proton-proton (PP) chains. The PP-chains do not require the presence of metals, so Population III red dwarfs can exist.

The British TV programme[edit]

I believe it was a children's television programme. I suggest we change the link to say: "For the British children's television programme from the 1980s..." - — Preceding unsigned comment added by 138.37.7.247 (talk)

Erm, no, we shouldn't, as it wasn't. --Neo 22:11, 1 February 2007 (UTC)
Okay, but I can't find anywhere that states it's not a children's programme. Could we please then highlight that it's an adult programme, and provide some kind of reference to support this detail? Thanks. —The preceding unsigned comment was added by 138.37.107.212 (talk) 20:00, 4 February 2007 (UTC).
I think we shouldn't because I'm not confident that you are acting in good faith here. Given the time the programme was shown (I'm guessing you are British given the way you've spelt programme) was post watershed, and the content was quite clearly adult themed I don't see how anyone could mistake the show for a children's programme. --Neo 20:50, 11 February 2007 (UTC)
The shows on DVD are certificate 12. Definitely NOT a children's programme which are all certificate PG or U. QuiteUnusual 22:21, 11 February 2007 (UTC)
The main Red Dwarf television page now emphasises that Red Dwarf was adult-oriented, to avoid confusion. Somebody may decide to make the same change here, but I'm not going to suggest either way. —The preceding unsigned comment was added by 86.142.211.223 (talk) 20:48, 12 February 2007 (UTC).
Further to this comment I notice that this issue is considered "resolved" by the article for the television programme (see the discussion page), so we may as well put "adult-oriented" here too. I have made the change - hope this keeps everyone happy.
While I wasn't the person who removed the 'adult oriented' line, I must say that I agree with it having been removed - this is not a page about the show; in fact we don't need to say anything about the show here! I suggest we replace the whole thing with "For the adult-oriented British comedy series from the 1980s and 1990stelevision programme, see Red Dwarf." - this is akin to links on the page 'White dwarf' which lists
And indeed the Red Dwarf page which has simply 'For the type of star, see Red dwarf.'
In fact, I'm going to be bold and just make the change myself. -- Neo 20:17, 25 February 2007 (UTC)
Following that, should the RD TV article/link perhaps be "Red Dwarf (TV show)"? Right now all that separates this page from that one is the capitalisation of "d/Dwarf", which I can't help but think of as very bad practice. 193.63.174.10 (talk) 11:49, 21 September 2009 (UTC)
I think the tv show was actually for adults that acted like children, hence the confusion. Rich.lewis 01:18, 25 April 2007 (UTC)
In opposition, I prefer to apply Hanlon's Razor... 193.63.174.10 (talk) 11:49, 21 September 2009 (UTC)

Life on red dwarf planet[edit]

Is life probable on planet that revolves around a red dwarf ? —The preceding unsigned comment was added by 64.18.179.229 (talk) 20:17, 2 March 2007 (UTC).

There is a renewed interest in the possibility of habitable planets of red dwarf stars. Several papers on the subject appear in a new special issue of Astrobiology. Vegasprof 07:43, 9 April 2007 (UTC)
The article assumes plant life (and photosynthesis). On Earth, there's life that lives deep under the sea at thermal vents, that doesn't depend on any sunlight. http://en.wikipedia.org/wiki/Deep_sea_vents#Biological_communities It seems tidal heating could keep thermal vents active http://en.wikipedia.org/wiki/Io_(moon)#Orbit_and_rotation
Interestingly, does this mean that a non-star could still support life? (cool!) lionfish0 (talk) 18:06, 31 August 2009 (UTC) (lionfish0)

I am probably doing this wrong as I have never done anything to a Wiki, but I was curious in this article how it is mentioned that one of the difficulties in supporting life around a Red Dwarf was due to the fact that little to no UV radiation was emitted by such a star. However in this article from Space.com "Can Life Thrive Around A Red Dwarf Star" http://www.space.com/scienceastronomy/090409-sm-reddwarf-life.html It states that the difficulty is that UV radiation can be 100-10,000 more than normal. Well, if there were little to no UV radiation than 10,000 times more than almost none shouldn't necessarily be so big a concern. I feel like this entire article is full of factual errors, just based on scanning this discussion page and reading articles from more reputable sources. This is a much more glaring error than say the artist rendition error mentioned above. Someone who knows more should really fix this before misinformation can confuse too many people. —Preceding unsigned comment added by 184.56.26.53 (talk) 14:53, 10 December 2010 (UTC)

link color?[edit]

Why are the links to other articles in this page red? 140.198.172.119 17:52, 10 May 2007 (UTC)

I can only see one red link in the article - maybe it was the computer you were using having odd internet settings? --Neo 18:00, 10 May 2007 (UTC)

When they leave the main sequence[edit]

Hi, what happens when a red dwarf runs out of hydrogen? Are they massive enough to swich to helium fusion and become red giants, as the sun will in 5 thousand million years (sorry, still reluctant to adopt the short scale)? Yeah, I know no the universe is too young for a red dwarf to have run out of fuel anyway, but I am just curious... Steinbach (fka Caesarion) 15:21, 12 May 2007 (UTC)

The article on stellar evolution states that 'A star of less than about 0.5 solar mass will never be able to fuse helium even after the core ceases hydrogen fusion' however apparently if the core is not fully convective - i.e. if there are stratified layers inside the star then 'it will develop into a red giant ... but never fuse helium as they do; otherwise, it will simply contract until electron degeneracy pressure halts its collapse, thus directly turning into a white dwarf.' --Neo 21:18, 12 May 2007 (UTC)

Steller Evolution[edit]

I thought that the White dwarf stars gradually cool to become Red dwarf stars, on their way to evolving into Black dwarf stars... is that true, or are these completely separate stars, like Brown dwarf and Sub-brown dwarf stars? (i'm asking becuase i was taught that stars go from white to red to black in grade 5, but i was always skeptical of that. RingtailedFoxTalkStalk 17:18, 12 May 2007 (UTC)

Yes and no - Yes, white dwarves will cool and emit radiation in the red region - see here, bt they're still called white dwarves, not red dwarves to avoid confusion with the stars presumably. --Neo 21:18, 12 May 2007 (UTC)
White dwarves are partially collapsed stars comprised of degenerate matter (not neutronium however) - they are the final stage after (elderly) red giants of roughly the same mass as our sun. A red dwarf masses much less and never collapses because its mass can be supported by interatomic forces. Although white dwarves will eventually cool and radiate longer wavelengths, the universe isn't old enough for white dwarves to have turned red yet! When that time comes, two stars of these types might have roughly the same size, color, and temperature, but would still be totally different. (Apparently all kinds of strange ideas are taught in elementary and secondary science classes in America these days. It was not always so... ) The different kinds of star are mostly determined by mass. The larger, the brighter and shorter-lived, and the more likely to turn into a bizarre object. The smaller, the darker and longer-lived. Please read up on this if you are interested.Vendrov 07:53, 21 September 2007 (UTC)

Planets[edit]

SOmeone more knowledgeable than me needs to re-add the Planets section. I just blanked it because other than the heading Planets the section was empty except for the words, "Eat anus." Basejumper2 12:54, 25 October 2007 (UTC)

I changed the section marked "Detection" to "Planets", because the section actually discussed only detecting plants (or rather, listed recently detected planets) rather than detecting Red Dwarfs. --Noclevername (talk) 01:24, 5 March 2008 (UTC)

I’m fine with this change. It’s correct since the detecting went mostly for plants. --DavidD4scnrt (talk) 06:59, 10 April 2008 (UTC)

The planets here are only the new ones from 2005 and later. There are several planets orbiting red dwarfs, so I think we should create an article called: List of red dwarf planetary systems or something. I'll try to gather up enough info for it. --UltimateDarkloid (talk) 12:23, 15 September 2008 (UTC)

Gliese 370 b is mentioned at the end of the planets section but Gliese 370 isn't an M dwarf, or even a late k dwarf, it's a K5V and so doesn't that make Gliese 370 an orange dwarf star? Perhaps, if you want to mention it anywhere it should maybe be put into the K-type main-sequence star article. — Preceding unsigned comment added by 86.128.86.65 (talk) 03:00, 24 March 2012 (UTC)

I removed the paragraph on Gl. 370 from this article. Thanks for the catch. Regards, RJH (talk) 21:30, 16 April 2012 (UTC)

WikiProject class rating[edit]

This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 10:02, 10 November 2007 (UTC)

Too red, too red[edit]

That "artist's conception" of a red dwarf is simply far too red. An ordinary incandescent tungsten light bulb radiates at about half the temperature of a red dwarf. Its light is a soft yellow-orange-white against daylight and comparatively nearly white at night. Red dwarf stars just aren't that ... red. 68Kustom (talk) 15:39, 5 September 2008 (UTC)

Depends on the Spectral type and mass of the Red Dwarf. There are those that are dim and look almost like Brown Dwarfs and those that are slightly orangish, --UltimateDarkloid (talk) 12:23, 15 September 2008 (UTC)

They'd still be bright yellow-orange-white, not dark ember/ruby red as depicted on this page. But it's part of one of the most far-reaching misconceptions in stellar astronomy: the actual colour of stars. I mean, try to argue that Procyon isn't yellow-white (it's bluish-white) ... heck, the latest Astronomy mag has pictures of Capella (white) and Betelgeuse (yellow). —Preceding unsigned comment added by 68Kustom (talkcontribs) 05:05, 31 December 2008 (UTC)
I agree with your point. The red coloration is primarily based upon how the human eye perceives the hue of a point light sources at night. This article has a good discussion on the topic, while here is a table of star colors based upon their blackbody temperature. As an example, I attempted to provide a more realistic appearance of a red dwarf in the File:Alpha centauri size.png image, with base colors based on temperature and luminosity showing greater saturation toward the center of the star (the opposite of limb darkening, I suppose). :-) The File:Mira 1997.jpg image shows something comparable for an M7 class star, although I'm not sure if the colors have been adjusted.—RJH (talk) 20:52, 12 November 2009 (UTC)
1. You all know: "artists conception",
2. 68Kustom, the misconception comes from the 19th century studies of star colors without spectroscopy before color photography: my private experience with trying to observe the colors of the stars by naked eye and binoculars indicate that the names describe a weak nuance deviation from clean white, so that stars that are actually orangeish pink (fex Betelgeuze) are called "red" and stars that are actually bluish white (fex Rigel) are called "blue". So "red" should be translated to "pink" or "orangeish pink". Rursus dixit. (mbork3!) 08:40, 20 November 2010 (UTC)
3. The image is PD, so remixing it to a realistic color would be acceptable and desired. Rursus dixit. (mbork3!) 08:49, 20 November 2010 (UTC)

What is a red dwarf?[edit]

I think the general conception of the noun phrase "red dwarf star" gives the impression that "red dwarf stars" are stars that are very tiny and red. Not so. I believe "red dwarf star" are low mass stars that are fully convective and not giants, i.e. only fusing hydrogen to helium, not helium to carbon (nor oxygen). They're residing on the lower "red" end of the Hertzsprung-Russell diagram, which is the lower red extension of the main sequence. They're pinkish and orangeish because of low surface temperature, which translates to "red" in astronomy jargon. Rursus dixit. (mbork3!) 08:49, 20 November 2010 (UTC)

Grammar in the lead[edit]

From Earth, no red dwarfs are visible to the naked eye.

Let's replace the subject "no red dwarfs" with "none"

From Earth, none are visible to the naked eye.

None is not simply a singular combination of "no one". It can act as a plural for "not any". In this context, the subject (red dwarfs) is plural, and appears as plural in the sentence directly preceding. Therefore, the proper usage is "none are" which is plural. The user asked me to look it up, and I did before they told me and found several sites: [1] [2] [3] [4] The first time I read that sentence I knew it didn't sound right, and I was correct. "None is" is used for singular subject (Not one red dwarf IS visible to the naked eye) but in this case the preceding used plural, therefore it is No red dwarfs ARE visible to the naked eye. Cadiomals (talk) 15:33, 28 September 2012 (UTC)

The question is not whether "none are" can be correct; the question is whether the sentence is correct as it was written and intended. You cited purely tendentiously; none of those sources are authoritative and you failed to cite any of the many in support of the present syntax and you also failed to acknowledge the allowance for the present syntax even in what you cited. It’s at the writer’s discretion. See, for example, [5]. “Not one is visible to the naked eye.” Is there some reason you hate that? The right thing to do here is to change the sentence to something that isn’t going to cause this sort of dreary edit churn. Strebe (talk) 20:32, 28 September 2012 (UTC)
I was not arguing that the use of "none is" is incorrect. I was arguing that the use of "none are" is just more fitting in this context. Maybe none of my sources were very authoritative but they all had a common consensus that "none are" is used with a plural, and I could find ten more.
The pair of sentences is: "However, due to their low luminosity, individual red dwarfs cannot easily be observed. From Earth, none is visible to the naked eye." In the first sentence, the plural "red dwarfs" is used, and the second sentence is directly connected to the first. This lead me to believe "none are" is more fitting here. It is not incorrect, but it lacked fluidity and never sounded right to me the moment I read it, and I was afraid it would bother other readers. But since I don't want to be debating such small details any longer, I will settle for the use of "not one" as a reasonable compromise even though it sounds too sharp to me. Cadiomals (talk) 21:37, 28 September 2012 (UTC)
By your reasoning, it would never be proper to write "none is" because the context is always a group. That’s what “none” does: It excludes the group. It never excludes the singular. The context you need to examine is the syntax within the sentence, not what’s going on in sentences around it. In the simplest case, “None is a friend,” vs. “None are friends.” English wants to distinguish between singular and plural, but it forgot about nongular (and it is equally awkward with collective nouns). To try to cope with that, we de facto transfer the subject to “friend” or “friends” and away from “none”. Strictly speaking, that shouldn’t be allowed, but that’s how English has evolved to (more or less) deal with its omission. In sentences like the one in question, there is no syntactical resolution; either way is equally reasonable and hence we are obliged to defer to the original writer. The “sounds wrong” argument doesn’t work. It sounds right to plenty of people. Strebe (talk) 01:38, 29 September 2012 (UTC)

Reconciliation between minimum mass for self-sustaining fusion and red dwarf minimum?[edit]

In the article on STARS, it is stated that low metallicity protostars with a mass of 87 x Jupiter's is the lower bound for star formation. Here, the lower bound is 0.075 x Sun's mass which is about a factor of 7 lower. I think this seeming discrepancy needs explanation.216.96.76.236 (talk) 22:23, 20 June 2013 (UTC)

Your "factor of 7" is the only discrepancy here. Strebe (talk) 09:32, 21 June 2013 (UTC)

update[edit]

The section "planets" ought be updated after the discovery of Kepler 186f187.59.103.179 (talk) 19:49, 19 April 2014 (UTC)