Talk:Red dwarf

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[edit] This article is completely and obviously stolen from an astronomy book. It is astonishing that someone made sections for a clear case of not only copyright infringement, but something they never intended to improve.

The information in this article is out of date and this problem has not been addressed because evil morons are reaching for the shelf. Please defer to accepted astronomy and behave like newspaper reporters rather than people who cheat in school.

[edit] Metallicity

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.

[edit] Giant dwarfs

I disagree with this statement:

Red dwarfs never initiate helium fusion and so cannot become red giants

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)

[edit] Population III stars.

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.

[edit] More on Population III Stars

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

[edit] Carbon

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.

[edit] Nucleosynthysis

This statement does not seem right to me

Since a low mass star fuses hydrogen in the presence of metals, then an early protostar of such a low mass devoid of metals would not 'go nuclear', it would simply sit around as a clump of gas until more material came along.

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.

[edit] The British TV programme

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
  • For the magazine, see White Dwarf (magazine).
  • For the song "White Dwarf" by a-ha, see ppAnalogue]].
  • For the movie "White Dwarf", see White Dwarf (movie).
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)
I think the tv show was actually for adults that acted like children, hence the confusion. Rich.lewis 01:18, 25 April 2007 (UTC)

[edit] Life on red dwarf planet

Is life probable on planet that revolve 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)

[edit] link color?

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)

[edit] When they leave the main sequence

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)

[edit] Steller Evolution

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. RingtailedFox • Talk • Stalk 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)

[edit] Planets

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)

[edit] WikiProject class rating

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)