Talk:Red giant/Archive 1

Archive 1

Question

Is it that all stars go through the 'red giant' stage, and then branch off into white dwarfs, black holes, and neutron stars due to their masses? Or is it that the red giant stage is specific to white dwarfs?

Ahh... I see... after some research, I understand that the red giant stage is indeed a common state for all stars, and the branch off is after this, as to which final state they end in (depending on their masses).

That's how I understand it, too. The red giant stage is a branch point, and then, for example, our Sun will specifically branch to white dwarf (bigger mass stars will branch differently). FriendlyRiverOtter 06:20, 8 April 2007 (UTC)

This makes no sense (re: The sun as a red giant)

"It is calculated that the Sun will become sufficiently large to engulf the current orbits of the solar system's inner planets, up to Earth, and its radius will expand to a minimum of 200 times its current value."

The earth's orbit is more than 1,000 times the radius of the sun. How would the Earth's orbit be engulfed by a Sun which is only 200 times its current radius? —Preceding unsigned comment added by 74.95.93.253 (talk) 22:35, 19 May 2011 (UTC)

I question this part...

"As Earth's Sun is of one solar mass, it is expected to become a red giant in about six billion years. It will become sufficiently large to engulf the current orbits of the solar system's inner planets, including Earth. However, because the gravitional pull of the sun will have weakened, it is unlikely that the planets themselves will be engulfed."

Why would the gravitational pull weaken? The same amount of mass will exist as there was before, so as long as the planet isn't actually enveloped, it feels the same strength of gravity... is there something I'm not accounting for here?

The Sun will have lost a bit of mass during the next few billion years; if nothing else, due to its energy expenditure, and the solar wind. Ben Standeven 20:28, 12 Jun 2005 (UTC)

When the Sun is about 12 billion years old stronger solar winds will begin to blow, and over a period of a few million years the Sun will shed about 28% of its total mass by losing the outer parts of its envelope to this wind. The lower mass of the Sun will result in less central gravity in the Solar System, and the planets will move slowly outwards in their orbit: the Earth will move out to about 1.4 AU. See The Once and Future Sun Eroica 10:07, 7 November 2005 (UTC)

Why does the sun expand to beome a red giant why does it expand especially when the core contracts.

Why the Sun expands

I am not an astrophysicist, but I believe the sequence goes as follows:

When you see the visible surface of the sun, you're not seeing the actual place where fusion is happening -- the light you see actually originated in the core. Think of the Sun as like a common frosted light bulb -- although the round glass surface of the light bulb appears to glow, the light really originates from the filament deep within. The filament is very hot; the glass surface (while hot to the touch) is nowhere near the same temperature.

The outer layers of the Sun contain hydrogen, just like the core does, but it's too cool to undergo fusion. Yet.

The core of the Sun is a place of two opposing forces: gravity causes the mass of the outer layers to push inward, and the explosive fusion reaction is constantly pushing outward. But when the available hydrogen in the core begins to run out, there's less of a reaction happening to counteract the Sun's own gravity. The Sun begins to contract a little, squeezing the core tighter.

But that squeezing increases the pressure at the core, pushing the atoms closer together and driving the temperature up -- that's what happens when you squeeze gas into a smaller volume. At some point, the temperature gets hot enough to fuse the waste helium that was produced from fusing hydrogen. So now the core is burning very hot: not only hot enough to push back against the weight of the outer layers, but also hot enough to cause those layers to ignite.

These outer layers are not under the same immense pressure as the core (since they don't have the weight of the entire Sun on top of them), so they are more free to expand. It's like setting off a bomb on the surface of the Earth as opposed to setting one off which is encased in solid rock a mile down: the first bomb will displace a lot of the surrounding atmosphere, while the second one will displace only a small amount of rock.

So the Sun expands. A lot. I think that the ultimate radius is under dispute -- some people seem to think it will swallow the Earth, some think it won't -- but regardless it'll kill off anything on the surface.

Eventually the hydrogen in the outer layers will burn up and, lacking the explosive outward pressure, they'll gradually succumb to the Sun's gravity again. The Sun will contract, only this time there's simply not enough mass to make enough pressure in the core to drive the temperature up high enough to start another cycle of fusing heavier elements. The Sun keeps contracting, growing redder and fainter, like a dying ember.

Yes. Except the story is too long, and contains too many similes that deviates from the basic connections.

The basic mechanism boils down to the following: a high-concentration energy production implies a vast difference between the zero energy production outside the star, a difference that needs to be "bridged" by some energy transport mechanism, namely radiation transport ("wandering photons") or convection ("boiling"). The more concentrated energy production, the larger and redder the star, and conversely the more "diluted" energy production, the smaller and bluer the star. Rursus dixit. (^mbork³!) 09:43, 5 August 2011 (UTC)

Color doesn't appear red

As I understand it, Red giant stars don't look red. They are red because they are cool. They are called red giants because the main electomagnetic output is infrared radiation. To the eye, they still look white. My reference is from the magazine Analog dated 2-5 months ago, but I don't have it here and can't look it up. --Djfeldman 14:10, 26 July 2006 (UTC)

A red giant would indeed look white, if viewed close enough because its intense light of saturates cone cells. However, viewed from a distance red giants look orangish. For example Betelgeuse looks clearly orange compared to other stars in Orion. But you're right in that red giants (or other class M stars) never look red. There's exception, the carbon stars, which are deep red.--JyriL ^talk 14:49, 26 July 2006 (UTC)

How Fast

Once this Red Giant phase starts, how much time does it take to complete? I read years ago, that it bloats to Red Giant in a matter of hours. Now that astro-science is more developed is that still the theory?

Fiction

*Within the Dune Universe, The Sun is in its Red Giant phase during the events that take place in The Butlerian Jihad. The book being the first of three prequel Novels. Written by Brian Herbert and Kevin J. Anderson. Current estimates require 4.5 billion years for the sun to reach its red giant phase.

The author makes a confusion between the star of the stronghold of the machines, the planet Corrin (indeed a Red Gigant), and Earth. Butlerian Jihad takes places more or less 3000 AD.

--57.68.24.50 09:06, 16 November 2006 (UTC)

I re-added the bit about the Dune universe because, as you mentioned, a Red Giant is a part of it. Could you fix it up to reflect the concerns you stated above? Thanks! --benwildeboer^{(talk - contribs)} 12:11, 16 November 2006 (UTC)

I fail to see how it is beneficial to the understanding of Red Giants to list every single mention of red giants in fiction in this article. Such trivia sections are little better then internal linkspam promoting other articles which are barely related, if at all. Removing. -00:31, 25 February 2007 (UTC)

I'm a strong proponent of removing trivia from articles, but I don't think this fits. It's hardly every single mention of Red giants in fiction, but rather three very influential examples of how this stellar phenomena has influenced culture. Superman wouldn't be Superman without a red star. CovenantD 00:45, 25 February 2007 (UTC)

The section as it exists hardly qualifies as an explaination of the cultural influnce of red giants. Currently all that section contains is a bunch of disjointed facts that just happen to involve a red giant in some sense. There is no explaination for why the red giant is significant. Does it signify some cultural theme? Strength? Age? Death? (See FBI portrayal in the media for an example of a good "in popular culture" article). If all that the trivia section is going to contain is a random list of trivia then we're better off without it since all it's going to do is encourage every fanboy/fangirl out there to start injecting their own favored novel/anime/game in there. -Loren 00:54, 25 February 2007 (UTC)

Suspiciously precise

"They are stars of 0.4 - 10,515,478 times the mass of the Sun"

Where does the second number come from that it is justified in being given to 8 significant digits?

Timeline of Earth may be incorrect

I would like someone to review this for correctness:

Earth's biosphere will be destroyed as the Sun gets brighter while its hydrogen supply becomes depleted. The extra solar energy will cause the oceans to evaporate to space, causing Earth's atmosphere to become temporarily similar to that of Venus, before the atmosphere is also lost.

I understand that the Earth will lose its oceans and biosphere before the Sun becomes a red giant. The Sun is slowly brightening while on the Main Sequence at a rate of about 10% every billion years. By the time the Sun nears the end of its life on the Main Sequence, its increased luminosity will long since have boiled the oceans and destroyed the biosphere. When the Sun becomes a red giant, it won't boil the oceans at that time. Instead, it will become hot enough to melt the rocks. --B.d.mills 04:30, 6 June 2007 (UTC)

You may well be correct. Someone has probably written a paper on this. Finding it would mean scanning the ADS

That show on top is right. You probably got the info from website still uses the old calculations.

Answers about Earth timeline

Some people may still rely on Planetary nebula and Future of our solar system. They still mention what early calculations. They thought sun will expand 100 times current size swallowing Mercury and Venus and maybe even Earth, even if not; Earth would be hot enough to melt rocks. The previous calculation shows sun would penetrate 90 percent to Earth orbit they suggest the gravitation pull might tuck in the Earth orbit causing the Earth orbit to decay perhaps due to orbiting sun's outer atmosphere.

Venus' Sun

[1] The new calculation shows all planets but Mercury will escape to a wider orbit. It would be large enough to penetrate Venus orbit but in 5 Gyrs, but it's decide that Venus will not be swallowed up. It will first reach 0.8 AU just slightly past Venus orbit. Because it's loss of mass and gravity Venus will escape to 1.0 AU by then. Instead Venus will just be a hot enough to melt rocks making the surface semi-molten, and it's greenhouse atmosphere will long been gone, and viewing from it's surface you will see sun at daytime filling the whole sky, sunrise and sunset you will see 75 percent of huge sun and nigthtime sun will fill 40 percent of sky. Mercury will completely be incorporate in the sun's inner layer structure for envelopment and it will get eliminated and engulfed, and destroyed. Earth will just be scorch cinder it won't be that hot just oceans and atmosphere will be escape off into space. Yes' it's ocean will evaporate, biosphere will certainly be destroyed, Venus will still be alive since it will escape to a wider orbit. Earth will be slightly cooler but not much. That is a good news Venus will not be swallowed up when sun dies, but the chance to support life is much more impossible. The link regarding to the new calculation I show you it the blue title above. Freewayguy 01:11, 27 July 2007 (UTC)HPShu789194

Definition of Red Giant!

The text says (11:01, 11 August 2007 (UTC)):

According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. Examples include Aldebaran, in the constellation Taurus, and Arcturus.

This is ... no good! (politely said). A red giant burns helium to carbon. Said: Rursus ☻ 11:01, 11 August 2007 (UTC)

That was wrong too! Red Giants are swelled-up stars that burns H in a shell, and increases its core pressure and temperature. When fereretrerererere (sorry) ... when the helium core burning starts the star is now a horizontal branch giant. I'll fix it as soon as I'm able to, if nobody is faster than me. Said: Rursus ☻ 13:28, 11 August 2007 (UTC)

Now fixed by enhancing this red giant:ing to also include such swelling shell H-burners. With reservations for errors and ambiguous meanings of "Red Giant". Said: Rursus ☻ 14:54, 11 August 2007 (UTC)

It is not that simple. Stars with solar mass become red giants twice, once burning hydrogen in a shell (the RGB) and again (after a period of core helium burning on the so-called horizontal branch) burning helium in a shell (the AGB). The defining features of a red giant are low effective temperature (they are red!) and a large radius (they are giants!) Timb66 22:56, 11 August 2007 (UTC)

Good note, we'll see how we can include that information. That Red Giants come in RGB, AGB and Horizontal Branch (Red (?) Giant) is something it would be nice to pinpoint, but it starts to become a little complicated there, so maybe that should be second sentence, or some such... ? Said: Rursus ☻ 08:37, 13 August 2007 (UTC)

I'll take a tour reading some before "messing" any more with the text. One problem is the "redness", below what T_eff is the star "red"? Are there ambiguous definitions around? Etc. ... the usual encyclopedian linguistic questions. Said: Rursus ☻ 09:03, 13 August 2007 (UTC)

My usual mumbling, here:

• Definition of a Red Giant Star – NASA, don't take ad notam, a survey on sci articles are needed to determine a proper "definition";
• Red Giants - just a nice edu link;
• David Darling: red giant – An evolved giant star [!!!] with a surface temperature of 2,500 to 3,500 °C, a spectral type of M or K, and a diameter between 10 and 100 times times that of the Sun, that's a definition, actually!
• The Columbia Encyclopedia, 6ed red giant – haahumm!
• Dr. Sten Odenwald: Red giant – a concise and good one – not actually defining anything (definitions cause troubles)
• Pulsing red giant glimpses at Sun's future – perfectly irrelevant but might deserve an article on WP.
• Red Giant Star – hard-to-read technical explanation that (AFAIK) seems to be accurate and very usable for further development of the article.
• [2] and [3] two term using texts!! This is what I'm after!! Just read the 1st one:

RGB stars are objects with masses lower than ∼2.0 M⊙ (the precise value depends on the initial chemical composition), which develop electron degenerate He-cores after the end of central H-burning, surrounded by a thick H-burning shell (thickness of the order of 0.1 M⊙ ) and a convective envelope whose chemical composition is the initial one. The envelope temperature gradient is to a large extent adiabatic, apart from the most external layers, where it becomes superadiabatic, and must be treated according to some prescribed convection theory.

This is a concise definition, but it is for RGB stars: in essence:

1. the mass is < 2 Msun,
2. the core is degenerate He,
3. a H-shell contributes energy,
4. the envelope (atmosphere) boils like boiling water (but gas of course).

One slight correction to what you written here: stars on the horizontal branch (which is basically the main sequence for core helium burning) are not red giants. The HB phase of a star comes in between the two red giant stages. Timb66 10:26, 13 August 2007 (UTC)

That sounds reasonable, and that was one of my main troubles, the other ones being:

1. Is red giant ever "defined", or discussed by a "prototype" consensus, the latter being the usual case in a language.
2. If the temperature limits are 2,500 to 3,500 °C, as from David Darling, then what to do about early C-R who matches late G-stars?
3. Only the carbon stars are actually red, the rest being orange or maybe yellow, what to do about the S-stars?
4. Some pair of colliding wd:s are theorized to become a red giant, what to do about them?

The solution would be to go back to the discoverer, then whome of Hertsprung or Russell? Or maybe Cannon or someone else? Said: Rursus ☻ 13:27, 13 August 2007 (UTC)

It's like the definition of planet – it is straightforward until you have to actually do it. Said: Rursus ☻ 13:29, 13 August 2007 (UTC)

OK, doing a few hours survey on Hertzsprung, Russel, red giant descriptions and so on, the best we can do for now is to skip an outright definition of "Red Giant" (which might be a bad thing): instead,

A "prototypic" "red" giant is very inflated and has a low surface temperature, while at the same time a high luminosity. (Yellow orange to red in color). That's some kind of universal theme of all texts writing about "red giant stars". (There are no strict limits of definition for "red giants"). To this category of stars are generally regarded stars of K and M spectral types, the rare S class stars, and also the carbon stars, of the spectral types C-R and C-N. The inflatedness is due to the electron degenerate cores.

To the red giants belongs stars in the Red Giant Branch (RGB) that have ceased "burning" hydrogen in the core, and now instead "burns" hydrogen in a shell. Red giant stars belonging to the category Asymptotic Giant Branch (AGB) instead have ceased burning "helium" in the core, and so burns it in a similar shell. RGB and AGB stars occupy almost the same place in the HR diagram, the AGB diminutively above the RGB:s. There are theories about other astrophysical mechanisms for some red giant types, for example the R CrB stars .........

Soon... Said: Rursus ☻ 18:04, 13 August 2007 (UTC)

Done. Please criticize as fitting. Said: Rursus ☻ 18:41, 13 August 2007 (UTC)

More to do on article

More todo:

1. some more about different red giant types, AGB, RGB, possible wd merger cases, variability, Barium stars (not!) and other unnatural critters, with links to their respective article,
2. examples of red giants, luminosity class shall be III (so not the superdupergiant Betelgeuse!),
3. rewrite the rest of the article – there's something odd written about Horizontal Branch vs. Red Giant, which was certainly correctly thought up, but is so garbled that it's hard to see the logic...
4. add a HR diagram, built from Image:HR-diag-no-text-2.svg, making a ring around the area of typical red giants.
5. planet munching, masers and suspected sub-photosphere giantplanets
6. restructure and rename the so called overview section, (since the first 3 §s are the true overview), it's not that far from good, but it's some little unclear, and may profit from sentence polishing, so that it makes a coherent whole message,
7. stress that horiz branch giants aren't red giants, but what about the red clump?

Said: Rursus ☻ 20:21, 13 August 2007 (UTC)

For high schools?

This article needs a complete re-write if it's to be used as a high school reference text. The writing isn't even at newspaper level. Example: "Red giants evolve from main sequence stars with masses in the range from about 0.5 solar masses to somewhere between 4 and 6 solar masses." Does anyone else find this wordy and redundant? 68Kustom (talk) 02:25, 10 February 2008 (UTC)

I agree that it is a bit wordy and redndant and that it needs to be proofread a bit to be considered a "high school reference text" 11341134a (talk) 00:35, 19 March 2008 (UTC)

Sun as a red giant

A new paper has been published: "Distant future of the Sun and Earth revisited" by K.-P. Schröder and Robert Connon Smith [http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2966.2008.13022.x] and also available on astrop-ph: [4]. Somebody might like to include this info (sorry, I don't have time). Timb66 (talk) 01:17, 29 April 2008 (UTC)

I have went through article and fix the informations. When sun turns yellow-orange, Earth would have evolve with runaway greenhouse effect.--Freewayguy ^{Talk Contribs} 00:33, 4 June 2008 (UTC)

First sentence

"...with nuclear fusion going on inside a shell inside the core but not in the core itself." If nuclear fusion is happening inside a shell inside the core, then nuclear fusion is happening inside the core (Transitive relation). Have I misunderstood? Is this (confusing) detail even necessary in the first sentence of the article? At this point in the article, I don't know what's meant by "shell" or "core", so the point is lost anyway.--Jmjanzen (talk) 19:43, 30 May 2008 (UTC)

It was wrong. I have removed from the lead. In fact, red giants have a core of helium (formed from earlier fusion of hydrogen) that is surrounded by a shell of mostly hydrogen in which fusion is occurring. In some red giants (AGB stars), the helium core is also undergoing fusion (into carbon). Timb66 (talk) 12:45, 4 June 2008 (UTC)

Sun's fate

Can sun actually get as big as Mars orbit?This size say sun's expansion can get up to 200 to 700 factors would be 1 and 1.7 AU. Mercury will be swallow up for sure; Venus can survive; but 80% chance no. Earth can survive; but 60% chance of Earth not to survive, Mars might survive about 80% and 20% chance of no. Few entries say Mars will be engulf but unlikely.--Freewayguy ^{Call? Fish} 23:39, 9 July 2008 (UTC)

Red and orange giants

I recall from my books as a kid that we called K-class biggies orange giants (?) has this changed? Cheers, Casliber (talk · contribs) 02:55, 16 July 2008 (UTC)

I've never heard the term orange giants, and all the astronomers I know call both K and M-class giants "red giants." That certainly doesn't mean the term "orange giants" isn't used elsewhere, but an Astrophysics Data System search for "orange giant" turns up 3 hits, while "red giant" turns up over 7000 . —Alex (ASHill | talk | contribs) 12:57, 21 July 2008 (UTC)

fair enough. I recalled it from books when I was a kid. Cheers, Casliber (talk · contribs) 13:16, 21 July 2008 (UTC)

Fwiw, Pollux is a giant with an orange hue, too hot (4500+) to fit the (2500-3500) temperature interval and vaguely smaller (8.8) than the (10-100) size interval... Wouldn't that fit into an "orange giant" category? -- Jokes Free4Me (talk) 18:36, 5 August 2012 (UTC)

Continual changes and reverts

This page has gone over number of changes and reverts. Venus earlier said it can also escpae to a wider orbit. Venus fate is not quite clear yet. We do have a few evidence of saying Venus will actually survive over sun's white dwarf but possibly not. So forget about tidal interaction then Venus orbit will roughly get to 1.3 AU. The older calcualtion is not actually wrong, just newer studies shows Earth will actually get pull in by Sun because of tidal interaction just like the fate, just make Venus less likely to survive.--Freewayguy ^{Call? Fish} 04:04, 18 July 2008 (UTC)

weird redefinition

There was some above discussion to the effect that red giant stars do not need to burn helium. I suggest whoever wants to argue such a point take a closer look at the article Red Giant Branch stars: the theoretical framework, which oddly was referenced above in favor of that point. In particular, note that dwarf stars can have degenerate He cores, which is the condition that results in a helium flash. In particular, if red giant stars can burn hydrogen alone, what do you propose fuels the dramatic expansion? Potatoswatter (talk) 05:18, 21 July 2008 (UTC)

I'm afraid you're mistaken. It's the gravitational collapse of the core, leading to increasing fusion rates in the shell, that causes the expansion of the outer layers. It's a bit subtle, so I'll just summarize the standard stellar evolution sequence for a solar mass star. (I get it from Zeilik & Gregory p. 320-322, which I added to the lead as a reference, but any astronomy textbook, the Sackmann et al paper referenced further down, or the Wikipedia stellar evolution#Mid-sized stars article has the same essential model.)

1. Hydrogen exhausted in the core. Core no longer supported by fusion against collapse, and collapses. This heats a shell of material around the core, which causes hydrogen burning in that shell to accelerate, which causes the outer layers of the star to expand into a red giant. The core is still not hot enough to begin helium burning; this phase of the star's evolution is called the red giant branch (RGB).
2. Core stops contracting when it becomes a degenerate gas (tip of the RGB, or TRGB). Continues heating until it's hot enough to burn fusion. Then helium flash occurs, and the star becomes a horizontal branch star (no longer a red giant -- "main sequence-like" helium burning phase).
3. When the helium in the core is exhausted, the star again becomes a red giant, this time on the asymptotic giant branch (AGB). Now helium burning occurs in an inner shell, while shell hydrogen burning (which has continued all along) continues in an outer shell. This is the only red giant phase when any helium burning occurs.

Dwarf stars do not have degenerate He cores; Solar mass dwarf stars will have degenerate He cores at the end of their RGB phase. Hope this helps. —Alex (ASHill | talk | contribs) 13:11, 21 July 2008 (UTC)

Thanks... I should check an astronomy book from the library, given how much time I spend reading WP and the internet... what confused me is that the term "core" refers only to the very center of the star. To go from "hydrogen burns in the core" to "hydrogen is depleted in the core" is misleading: in the first instance the core refers to the entire region of H burning and in the second the core refers to any He pit where H is not burning. Would it also be accurate to say that

1. In a dwarf star, H and He are mixed. The He concentration in the site of fusion, the core, gradually increases.
2. Eventually, enough He accumulates that it precipitates against fusion-powered mixing forces (convection, diffusion?) into a homogeneous mass, displacing hydrogen from the center of the core.
3. This alters the star's geometry such that the inert He mass is now the spherical core, and the fusing H mass is a surrounding shell.
4. From now on, additional work is extracted from the weight of infalling "exhaust" helium, boosting efficiency and output. (Is this a better description than "the core experiences gravitational collapse"?) This results in positive feedback as power rises with temperature. Especially at the onset of the red giant phase, there is much accumulated helium which all collapses at once.
5. A shell of depth X has greater volume than a sphere of radius X, so a greater volume participates in fusion?

Hope this helps improve & clarify. The language in most "accessible" webpages, and even giant star, really makes it seem like 1. H runs out 2. He flash 3. Red giant. Thx again, Potatoswatter (talk) 09:10, 23 July 2008 (UTC)

1 is accurate; 2–5 partially so, but I'll try to do the explanation in the article rather than the talk page. I've been meaning to work on stellar evolution (particularly stellar evolution#Mid-sized stars) for a while; that article has most of the right content, but it's not terribly well organized. I'll try to use this discussion as an impetus to actually get to work. My favorite textbook is Zeilik & Gregory (1998); stellar evolution is nicely summarized around p. 320. —Alex (ASHill | talk | contribs) 14:18, 23 July 2008 (UTC)

Rewrite/to do

I rewrote a large portion of the article, with a longish description of the evolution of a red giant, hopefully clarifying some of the points above. (diff)

Still to do (off the top of my head): the characteristics section could use expansion to discuss the internal structure of a red giant (convection, mostly) and the RGB/AGB stellar wind. A discussion of tip of the red giant branch and red clump stars as distance indicators would also help. The precise numbers for the masses at which behavior changes could be better referenced. (The numbers are somewhat uncertain and depend on metallicity, I think.) —Alex (ASHill | talk | contribs) 15:23, 23 July 2008 (UTC)

I could not find a source say the giant star is 2.57 the solar mass.--Freewayguy ^{Call? Fish} 21:26, 24 July 2008 (UTC)

Photosphere of RGs

do RGs have a defined photosphere like Sol ? HH 15:33 (CEST) 30 July 2008 —Preceding unsigned comment added by 145.254.95.134 (talk) 13:32, 30 July 2008 (UTC)

Giant (star)

Nothing in the section hdgs hints at a reason for Giant (star) Rdr'g to the accompanying article Red giant rather to the logical target Giant star. I'm changing the Rdr, and -- if needed -- relying on regular perusers of this page to repair the damage, and explain the need, in this section.
--Jerzy•t 07:56, 31 October 2009 (UTC)

• FWIW, the Rdr has been there since 2003 -- with edit summary "REDIRECT red giant ???" -- and the accompanying article became more than a Rdr to that Rdr to Red Giant (yes, an illegit dbl Rdr) only 2 years & some later! Case closed, i think.
  --Jerzy•t 08:06, 31 October 2009 (UTC)
  

Merge and redirect Red supergiant to Red giant

I think there is not enough unique information at Red supergiant for it not to be better treated as a section here. --SmokeyJoe (talk) 17:07, 4 May 2010 (UTC)

I think that instead of merging and redirecting, this article needs to be expanded. Red supergiants are very different conceptually from red giants due to occurring only with high-mass stars, i.e. ones that will eventually explode as supernovae, so having a separate article on these seems appropriate. Perhaps more can be added concerning the internal structure, shape, stellar winds, etc. and to highlight the distinguishing characteristics of these properties. --Jbuczyna (talk) 03:38, 25 April 2011 (UTC)

I agree with Jbuczyna that a merger is not appropriate. Our Sun can become a red giant, but our Sun can never become a red supergiant. -- Kheider (talk) 11:58, 7 June 2011 (UTC)

Epochal analyses

NASA’s Kepler Mission Helps Reveal the Inner Secrets of Giant Stars for the First Time contains astroseismological analyses that unambiguously determines whether a red biggie fuses hydrogen in a shell or helium in the core. Which means that red giants can be sorted into hydrogen burners and helium burners. Rursus dixit. (^mbork³!) 09:53, 5 August 2011 (UTC)

And this one (CoRoT) too! PDF freely available. Rursus dixit. (^mbork³!) 10:05, 5 August 2011 (UTC)

Needs of edits

An editor went through and messed up alot of the informations to the article. I was trying to read the information about Earth's fate and one editor just distorted the section completely. The previous context were fine until an user just screwed it up.

Did anybody payed attention? It consumed alot of time for me, the rest of the article body, I don't want to go through it and try to figure out which informations are right, that is why i just revert the whole thing to the way it were fine previously. Do anybody know why editors are so careless now a days. When users screw up the article on any subject they just left it messy and don't bother to fix it. I am getting tired of repairing the mess from careless editors. This is getting ridiculous. --69.226.39.147 (talk) 00:48, 26 February 2013 (UTC)

The editor who screw up the article is [5]. I noticed it when I was trying to read the information about future of sun.--69.226.39.147 (talk) 00:55, 26 February 2013 (UTC)

I was about to revert the recent edits (to something written in readable English) and then adjust the data as needed to match the more recent reference. However it occurs to me that this may not be the correct location for this section at all. There is a short section in Sun about this, then a long section in Formation_and_evolution_of_the_Solar_System, some information in Stellar evolution, then an entire article Future of the Earth. None of these currently describe the situation in quite so much detail with quite such recent references, but perhaps it is one of those articles that should be edited and the section here dropped. Or at least reduced to a quick summary and some links. Pending other thoughts, I'll do nothing for now. Lithopsian (talk) 11:51, 26 February 2013 (UTC)

The problem is you removed the information that was properly cited about Earth's fate (2008 by Smith and Schroeder) which was the most recent updated academic paper which was properly stated. Please do not change it again. I think we should just leave it alone.--69.226.39.147 (talk) 00:48, 27 February 2013 (UTC)

That isn't going to happen. The current version is grammatically awful and still contains contradictory and confusing information, so I am going to edit it one way or another. Calm down for a second, read what I wrote here, and help to decide whether the whole thing ends up in a different article or whether it stays here and gets corrected. Since yesterday, I'm even more convinced that this is the wrong place for a detailed explanation of this. Maybe a short paragraph and a link to the full detail. We don't need a blow by blow account of the future fate of the Earth in every article about a type of star that the sun might one day become. Lithopsian (talk) 13:54, 27 February 2013 (UTC)

I went through and fixed the section. I just linked an article attachment See also Formation and evolution of the solar system and Future of the Earth. I did simplify the informations about Earth's fate since recent studies shows Earth is likely to get swallowed up.--69.226.39.147 (talk) 00:37, 1 March 2013 (UTC)

I'll take that as agreement that the main detail belongs elsewhere. I have chosen Sun#Life_phases. I have expanded that section to contain the information from here, slightly rearranged but hopefully reflecting the latest research. Take a look, it will no doubt still need some tweaks. If that seems satisfactory, I will reduce the section here to a short paragraph and reference Sun#Life_phases for the detail. Lithopsian (talk) 22:16, 1 March 2013 (UTC)

Yes, it looks good at Sun#Life_phases expect when sun reaches tip of RGB it is 7.59 billion years in the future. Sun will leave main sequence in 5.4 billions years, it will expand only gradually every half a billion years until 7.59 billion years is when sun will expand suddenly. Yes, you may decrease the section here to short paragraph since you chose to move all the details to Sun#Life_phases.--69.226.39.147 (talk) 05:40, 5 March 2013 (UTC)

I think it would be very useful if we could provide the article with the graph which illustrates how fast the star will expand during the red giant phase and how fast it will contract to horizontal branch star. I wonder if somewhere there is data we could use. --Artman40 (talk) 10:34, 29 May 2013 (UTC)

Expansion rate

According to a habitable zone simulator, based on the data from University of Nebraska, the Sun does not contract before entering red giant stage (the star needs to be >2 solar masses to contract shortly before entering red giant stage). The significant mass loss for a solar mass star occurs mainly in 2 points: at the end of a red giant branch stage and at the end of the asymptotic giant branch stage. Sun also spends a fraction of a red giant branch being larger than 10 solar radii (less than 100 million years). --Artman40 (talk) 23:04, 29 June 2013 (UTC)

size

"Red-giant-branch stars have [...] diameters about 20–100 times the Sun (R☉)."

Do they have diameters 20-100 times the diameter or the radius of the sun (R☉)? — Preceding unsigned comment added by Darsie42 (talk • contribs) 17:33, 12 October 2014 (UTC)

Diameters are/should never compared with radii. I think there was slight case of mix-up: someone started talking about diameters and comparing that to the Sun and then also added the symbol for radius (or possibly someone else). I've fixed this. Thanks for noticing. --JorisvS (talk) 08:37, 13 October 2014 (UTC)

degenerate

In this set of articles could someone please explain the word 'degenerate'. Those in the know understand the meaning in this context but amateurs associate the word more with human attributes. I'm sure a supernova does not have peodophiles in it's core lol! Robotics1 — Preceding unsigned comment added by Robotics1 (talk • contribs) 11:04, 22 February 2015 (UTC)

It refers to the condition of degenerate matter. I've added a wikilink in the body of the text (it was already added to the lead section), so that readers there can also find it to find the explanation. That should be sufficient. --JorisvS (talk) 16:32, 22 February 2015 (UTC)

Lede

In the lede, it says "The appearance of the red giant is from yellow-orange to red, including the spectral types K and M, but also class S stars and most carbon stars." However, the Hertzsprung-Russell diagram to the right doesn't show a "Class S" star. If it's not on the H-R diagram but is correctly referenced in the lede, we should identify / describe a Class S star somewhere in the article.

Unfortunately, I'm too ignorant a layperson to do it reliably, and too busy right now to do the necessary research. I hope someone else will have the appropriate skills.

*Septegram*Talk*Contributions* 17:53, 26 April 2016 (UTC)

I've linked the lead to the article on S stars, which explains what they are. Lithopsian (talk) 18:02, 26 April 2016 (UTC)

Any recent studies?

Chances are that Milky Way & Andromeda are likely to collide each other in the next 3 billion years, thus increasing the chance to let sun swallow earth in the next 7.5 billion years and increasing the chance to let universe be in big rip in the next 22 billion years.

I see that the accelerating and expanding universe will be a commonplace so phantom energy will increase the chances of collision of Andromeda and Milky Way and Sun swallowing the earth and Big Rip. 124.106.137.86 (talk) 13:13, 30 April 2016 (UTC)

"The appearance of the red giant"

   The 5-sent (lead) sect is divided between 2 'graphs, the first of which closes with this muddy sent:

The appearance of the red giant is from yellow-orange to red, including the spectral types K and M, but also class S stars and most carbon stars.

My most plausible explanation of its intent would be this rewrite:

Red giants appear (at apparent brightnesses above the threshold for color vision) to the human eye as yellow-orange to red in color. They are most notably of spectral types K and M, but also include class S stars and most carbon stars.

My strongest concern is that the article is about this being a star type, of whose members only a finite number (and thus literally infinitesimal share) are inside the visible universe. (And my WAG would be that all but a figuratively infinitesimal (i.e., mentally incomprehensibly tiny) share of even those finite and relatively insignificant few will remain undetectable, to human senses and tech, for the next 50 to 1000 years.) For the time being, i'll wait in the hope someone better informed will be in the position to do an edit along those lines, without having to draw on more BOLDness than i currently care to.
--Jerzy•t 02:55, 17 May 2016 (UTC)

"Critique of Red Giant"

 The introduction is not informative enough

 Unclear to the common reader

 Diagram does not directly pertain to the Red Giant

 Impressed that it had 21 sources

 For 21 sources, the presentation should be better

 Even though the topic is hard to grasp, the writer of the page gives the reader

key words to be able to follow up with

The information presented in the page Red Giant is not geared for the common

reader to be able to actually understand the topic after reading the full page.

Understanding what the page is talking about would require having background

information on astronomy and the other topics being discussed. However, if

someone does have background knowledge on astronomy, this is an informative

page. It is clear that the authors of the article thoroughly researched the topic and

put a lot of work into it. It would be helpful if the article was simplified, and then

built up gradually to the more complex aspects of the Red Giant. MiriamShmueli (talk) 00:24, 8 November 2016 (UTC)