Talk:Stellar evolution/Archive 1

Text from 2001

Really good article. Would it be better if some of the topics were split in to separate entries - eg. Neutron star seems to work in isolation okay. --sodium

The Caption of the Crab Nebula

It states that the supernova occurred about 1000 years ago. However, the Crab Nebula is 6300 light years away. It seems like it should be written as the supernova occurring about 7000 years ago, unless this is just convention to use time of observation. 66.251.24.251 21:57, 16 March 2007 (UTC)

• It is indeed the convention to use the time of observation, since in astronomy distances aren't always well known. --Etacar11 23:45, 16 March 2007 (UTC)

Random Question

Random question from a reader, regarding the second paragraph of "Birth" talking about Giant Molecular Clouds, which reads: "The cloud is stable as its constituent molecules are too widely spaced apart for gravity to draw them closer." This doesn't really make sense, since gravity doesn't "cut off" at any distance. In contrast, the page actually *about* Giant Molecular Clouds, (at the bottom of the third paragraph in "General Information"), gives a different explanation: "The clouds have an internal magnetic field that provides support against their own gravity."

Of course that explanation doesn't cover (a) what would cause such a magnetic field and (b) how a magnetic field manages to keep a molecular cloud from collapsing since electrically neutral particles wouldn't be affected by magnetism -- but at any rate we have two pages linked to each other offering different explanations about what holds a molecular cloud apart. Anyone who actually understands astrophysics want to correct one or the other?

(Jan 8, 2005 -- It appears the "Birth" section has radically changed since this comment was posted and no longer contains the statement about particles being too far apart. Hence this comment is obsolete.)

White dwarfs

Updated first location where stability mechanism for white dwarfs is mentioned to link to degeneracy pressure. Although this entry does not yet exist a number of other astronomical entries link to it. It seems to have fallen down the cracks between the contributing astrophysicists and contributing quantum mechanics.

- Alan Peakall

Removed

Removed:

The ball, now a star, begins to shine.

The ball was already a star fusing hydrogen. Rednblu 11:02 20 Jul 2003 (UTC)

This text was replaced.

fusing iron does not liberate energy - because of the vast pressure and temperature, iron is actually forced to fuse. The supernova explosion is less than a fraction of a second away. Iron takes in energy when it fuses, it also takes in electrons. This energy and those electrons had been helping to support the star against it's own gravity. Now, with the support gone, the envelope of the star comes crashing down onto the core at a fine fraction of the speed of light. The implosion rebounds into a shock wave going through the star.

As the shock encounters material in the star's outer layers, the material is heated to billions of degrees, fusing to form the heavier elements. Indeed, all elements heavier than iron-56 are formed in supernovae explosions. In one of the most spectacular events in the Universe, the shock propels the material away from the star in a tremendous explosion called a supernova. The material spews off into interstellar space -- perhaps to collide with other cosmic debris and form new stars, perhaps to form planets and moons, perhaps to act as the seeds for an infinite variety of living things. Rednblu 11:57 20 Jul 2003 (UTC)

1st and 2nd Generation Stars

looking for more info about 1st generation and 2nd generation stars, and what times these have existed. particularly, our sun is 2nd generation; how does its age compare with other 2nd generation stars? is it one of the older? or one of the younger of such stars?

I woudn't call our Sun second generation, but it's recycled material. The life time of stars strongly depends on their age. The more massive ones burn out rapidly, the lighter ones have very long life times (much longer than the age of the universe). There is an entire population of old stars in the globular clusters, which form a spherical halo around what one usually thinks of as the galaxy, namely the central bulge and the surrounding disc. These could be called first generation stars, I guess. Stars form permanently out of the galactic gas, which is (also permanently) being replenished by supernova explosions. The latter occur when massive (and thus short-lived) stars reach the end of their life time, or in binary stars with mass flow between the components. The Sun's age is about 4.5 billion years, which is half its expected life span and one third the age of the universe. Gas from supernova explosions contains more heavy elements (like iron) than the galactic gas contains on average (because supernovae is where those elements are created). Therefore, the gas out of which the stars form becomes more and more enriched with heavy elemnents as the galaxy ages. The stars that form today contain more heavy elements than our Sun, which, in turn, is more metal-rich than the stars in the globular clusters.

Yeah, but that's precisely the question *e's asking, even if *e doesn't know the correct terminology. *I* don't know the terminology either, but I'm also looking for the same information. After the big bang, you'd have lots of hydrogen, which could form into stars, go thru fusion, and make stuff up to iron via reactions. You don't get any heavier elements in the universe until those "1st generation" stars go supernova. When they do go supernova, you get trace amounts of heavier elements due to the supernova reaction. Those elements are then available in clouds which can form stellar systems which can now have planets which consist of more than just carbon, silicon, iron, and oxygen, hydrogen and a few other light elements.

So, how long would it take for the fastest stars first created to go supernova, their results turned into clouds, and first set of "2nd generation" suns (which we are? or are we a third?) to coalesce? Does that make Sol one of the first 2nd generation stars (via age), or middling old for a second generation star?

~ender 2006-12-04 23:02:PM MST

The term you're looking for is stellar population. That term redirects to one titled metallicity, which is unfortunate, but the discussion there is OK. BSVulturis 22:53, 12 January 2007 (UTC)

Removed

i

Removed statement about astronomers objecting to the name evolution. I've never heard any astronomer object, and if there are astronomers who do, they are small enough in number so that statement doesn't belong in the first paragraph. Roadrunner 18:02, 4 Mar 2004 (UTC)

"Stellar Evolution" IS a Misnomer, Though too Late to Change

I am campaigning to make the usage of the term "evolution" more uniform in Wikipedia. I do NOT propose to change usage that is normal in a specialty, such as the use of stellar evolution. I am looking to make sure that what what I see (and hope others will see) as non-standard use of the term evolution is flagged in some way in every article the term is used, not just in a disambiguation page.

I suspect that use of the word "evolution" in "stellar evolution" is confusing to an encyclopedia reader. I am afraid that the biologists control the main use of the term. I hope that we can generalize from their use of the term to be able to use it in many disciplines in ways that will make it easier for discipline specialists to learn by analogy from other disciplines.

I note that before March 2004, the article contained language indicating that some astronomers did not favor the term "evolution", preferring something like "stellar development".

I believe that the term evolution in a scientific context refers to a process with four characteristics:

1. It refers to a change process in a population of relatively homogeneous individuals, not to the change of an individual member of that population.

2. It includes a process of replication of individuals in which the characteristics of the "ancestor" have a strong inflence on the characteristics of the replicate.

3. The process of replication involves significant variation.

4. The process involves some kind of selection that changes the relative frequency of the varieties of replicates.

I believe that "stellar evolution" fails the test. It seems to fail the first test in that it is largely (exclusively?) concerned with the development cycle of individual stars. I also do not see any replication process. The material of stars may be recycled but there doesn't seem to be much trace of the identity or characteristics of the previous stars remaining.

I would like some simple statement that the use of the term "evolution" in "stellar evolution" is distinct from its use in the life and human sciences. I am also applying this line of reasoning in the field of chemical evolution, which, however, does seem to mostly be about processes that DO fit the definition. Humbly proposed. DCDuring 23:52, 24 August 2007 (UTC)

The word "evolution" is used here to mean gradual development, which is the accepted meaning of the word in a dictionary. We can also talk about evolution of a language, of an idea, etc. The biological use, referring to the process of evolution by natural selection, is different. If you replace "scientific context" by "biological context" then I would agree with what you wrote. But otherwise I disagree. Timb66 10:53, 25 August 2007 (UTC)

Are you also going to complain about this use of the word evolution? —Preceding unsigned comment added by Caco de vidro (talk • contribs) 14:59, 11 November 2007 (UTC)

Biologists do not have a monpoly in the use of the word. Its first use was in a military context in 1616, and biologists were using the term in a different (ordinary English) sense in 1671, long before Darwin's grandparents were born! Dbfirs 21:37, 23 July 2008 (UTC)

Universe's Age

The article makes references to the age of the universe as though we are certain of it, but shouldn't it say that "it is believed that the universe is about 13 billion years old" and "The universe is not believed old enough for black dwarves to exist"?

We may not know the age of the universe for certain, but it's certain for all practical purposes (as certain as we are about anything else) that it's not old enough for black dwarves to exist. Black dwarves take hundreds to thousands of billions of years to come into existence.

As of 2003, we _have been_ certain of the age of the Universe to within 2%, thanks to WMAP data, and the scores of peer-reviewed professional journal publications such as this one detailing the data, its accuracy, confidence intervals, and normalization of its statistics to account for the models being considered. As far as the scientific community is concerned, the debate is over for the value of the age of the Universe. Of course, there are those who ignore scientific observations and data, and then there are the philosophers who can discuss the implications of this but science is science: the data has been taken, and it has been reported. It's up to you whether you accept the data and science, or reject it and believe something else in spite of scientific fact. But to do so would be a disservice to ourselves, and of course the Wiki articles to which we are contributing. Astrobayes 14:03, 20 June 2006 (UTC)

Helium-Carbon Fusion

Edited the statement about helium->carbon fusion lasting only "a few minutes" for a solar-mass star to the more generally accepted 1 billion years.

Heavier than iron

I'm confused with how an iron atom can be fused when being struck by a neutrino in supernova, I mean, wouldn't it break the nuclei apart? How does the additional protons and neutron fuse with the iron nuclei if just a neutrino made impact with it? (Sorry for asking easy questions I haven't studied in college yet)

- Protecter

I'm assuming its something related to neutron capture, just on a more fundamental scale. I mean, neutrons don't break the nucleus either, right? (Plus, they have more mass than a neutrino!) Perhaps the neutrino helps to form bonds or something. -- Natalinasmpf 14:42, 16 Apr 2005 (UTC)

I've changed neutrinos to neutrons in supernova section because neutrinos cannot form/alter nuclei at all and won't probably cause a shock wave compable to one caused by neutrons and photons. This should be reviewed though.

//lodin

• I believe neutrinos is correct here. --Etacar11 04:07, 11 May 2006 (UTC)

This is all quite confused in the article. The collapse of the iron core results in it being converted to chiefly neutrons, creating a core composed of neutronium. The neutron core collapse is halted by neutron degeneracy, which causes the momentum of the collapsing core to rebound, and which in turn causes the infalling stellar envelope (read: the rest of the star) to also rebound. The formation of the neutron core creates a massive amount of neutrinos, which are then emitted after it rebounds from its point of "maximum scrunch." This results in the neutrino pulse -- which is emitted before the electromagnetic event -- and actually contains most of the energy involved in the supernova itself. The rebounding envelope then creates what is traditionally thought of as the supernova, namely the star blowing itself apart. The pressures involved in the rebound, as well as induced reverse beta decay caused by the massive neutrino flux, are what synthesizer the heavier elements. What is left behind is the neutron core, which is called a neutron star. Xihr 06:46, 11 May 2006 (UTC)

• Yes, I think you are right, it might need some reworking, but when the person changed neutrino to neutron, that was incorrect. BTW, be careful about using the word "neutronium"--it is not really used in astronomy. Mainly you see it in science fiction. :) --Etacar11 22:24, 11 May 2006 (UTC)

It's also used by particle physicists, high-energy physicists, and astrophysicists dealing with collapsed stars. Don't believe everything you read in Wikipedia. ... But yes, your correction back to neutrinos was certainly correct. I was making a more general comment about the confusions that were going back and forth. Xihr 01:39, 12 May 2006 (UTC)

• Yeah, I get that. But I have to add: I'm not trying to start a fight, but I AM an astronomer and have NEVER heard one use the term "neutronium" seriously (and ADS finds no papers using it in the title) but hey YMMV (I can't speak for physicists [or all astronomers/astrophysicists] ;) ). --Etacar11 01:47, 12 May 2006 (UTC)

• The supernova article seems to get it right. The neutrinos do cause shock waves, so I was wrong in this part... However, how can neutrinos help creating heavier elements is still beyond my understanding, because you need baryons to do so -- and neutrinos are leptons, no matter what their energy is. //Lodin 2006-05-13 11:01 GMT

• Google "neutrino nucleosynthesis" and you'll find some info/references on it. --Etacar11 14:12, 13 May 2006 (UTC)

I already indicated how; induced reverse beta decay. nu + n --> p + e. Xihr 00:45, 14 May 2006 (UTC)

• Umm, stupid question maybe, but can someone provide actual papers and documentation on this. It seems like all this back and forth violates the WP:OR rules. No original research. If we don't know how it happens, we can't speculate. Either we know, and there's a citable source, or there's not, and don't include it. Maybe I'm misreading. But it seems like nobody ACTUALLY knows what goes on. Sounds like Pathological science to me. Pathological science, and Pseudoscience don't really belong in a good article (unless it's an article specifically about a pseudoscience claim or protoscience claim or religious claim [like Pastafarianism or Scientology]; assuming it's notable). So, if all we're doing is theorizing... Let's not. If it's controversial, it probably shouldn't be in there, or the controversy should be noted with notable resources on all applicable theories. Yeah? My 2c. Granted, I'm not a physicist. But when poeple start speculating, rather than using citable authoritative sources, Wikipedia says that's a 'no-no'... Mgmirkin 00:00, 19 October 2006 (UTC)

This discussion is not very speculative,at least not between physicists. I think this debatte has aroused because some people here tried to think about a supernovae without knowing all important processes. What comes out ist thinks like "oh i think this should be differt, because it can not be caused by the process i am familiar with". The only discussion i know about is whether neutronstar collisions provide a scenario likely to produce these heavy elements as well (or dominantly). Anyway if you want papers just go to google scholar and type "r process" almoust every paper you get (wich is not dealing with neutron stars) will tell you what i just told you. Here just some links:

http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v562n1/53839/53839.text.html http://www.journals.uchicago.edu/cgi-bin/resolve?id=doi:10.1086/174638&erFrom=2467619731031865010Guest http://www.journals.uchicago.edu/cgi-bin/resolve%3Fid%3Ddoi:10.1086/342230 Theo

OK, it goes like this: There is a shockfront of the infalling material, which bounces off the core. This shockwave now travels back, away from the core. Anyway, simulations show that they would not have enough energy and stop at some time. Fortunately the core sends a vast amount of neutrinos, which collide with the material giving it the extra drive to actually go out into space. Anyway, they just give new impulse and might cause some inverse betas. OK, now that the SN finally explodes you have to understand what a heavy nucleus actually is. We can characterize a nucleus by two numbers: number of protons in it (=Z) and total number of protons and neutrons (=A). Only some compositions of these two numbers are stable, others will decay. Roughly one can say you always need a few more neutrons than protons. So A = 2Z. All the incoming neutrinos can do is change neutrons in protons, but that leaves A unaffacted. If you want to create (for instance) lead (Z=82, A=206) you need to bombard Iron (A=56) with many many neutrons. NEUTRINOS WILL NOT DO. Luckily there is a good flux of neutrons appearing in a supernova, so iron catches some neutrons and may create the heavier (bigger Z AND bigger A) elements. So I assure you "neutrons" is correct. I know this because it is my topic of research. You will have noticed English is not my native language, and I am kind of in hurry right now, so feel free to correct anything you think is wrong with my language. Hope I could help you a little. Greetings Theo

Life Cycle

I assume stars have a life cycle, yes? This article seems to cover mainly just the evolution of a star, classifying them on mass, reporting on its death, then touching lightly on that it can later after its death (or becomes a black hole) be fed into new stars sometime later. This is ambiguous though, but I assume there should be some sort of life cycle or we would have run out of stars at the Universe's current age? Also, about blackholes trigerring nebulae as well? -- Natalinasmpf 14:37, 16 Apr 2005 (UTC)

The article should make it clear in the first paragraph that a star is believed to form by a cloud-collapse model in a stellar nursery within a nebula, generates core temperatures high enough for fusion to occur, and then spends most of its life burning hydrogen in the main sequence, after which a number of old age scenarios are possible depending on mass and composition. SamuelRiv 08:49, 4 December 2007 (UTC)

giant molecular cloud

For this phrase, is molecular cloud not better link as dark nebula? -- Harp 10:54, 19 May 2006 (UTC)

• I have a dumb question. Has it ever actually been shown that a giant molecular cloud collapses under its own gravity or whatnot to create a star (I mean have we ever actually seen gas collapse in a vacuum with no force other than gravity)? Or is that just a theory that's accepted as fact despite not ever having actually witnessed it? Just wondering... Never personally seen a cloud condense into a star. So, how do we know it happens? Or is it just in fashion until we figure out it doesn't really work that way, or we do figure out what ACTUALLY happens? If someone could point me to actual experiments showing how gases in a vacuum condense into solid matter (like Earth or the sun; okay, granted the sun's not "solid", but more so than ambient gas/plasma in a vacuum), I'd be interested to know. Just wondering. Mgmirkin 00:06, 19 October 2006 (UTC)

As with much of astronomy, this isn't something that can be tested in a lab since it's impossible to recreate the conditions. Physcis tells us that if a gas cloud has enough mass it will collapse under its own gravity in a free fall time (assuming nothing else slows its collapse). Check out the page on Jeans instability for the related equations. A typical giant molecular cloud, with mass of roughly 1 million solar masses, takes something like one million years to collapse. So, we'll never be able to 'watch' a cloud collapse. We can, however, look at many different moluecular clouds and see the varying stages of collapse and star formation. A good place to read up on the research in regards to star formation is the book "The Origin of Stars and Planetry Systems." Its a collection of papers from a conference a few years back and includes some good summary articles, however, it is written for other astronomers, so depending on your background it may be rather boring to read through.

Brown dwarfs

Brown dwarfs heavier than 13 Jupiter masses ($M_{J}$) do fuse deuterium, and some astronomers prefer to call only these objects brown dwarfs, classifying anything larger than a planet but smaller than this a sub-stellar object.

Could someone clarify this please? Should the latter term read sub-brown dwarf? I was under the impression that brown dwarfs are sub-stellar objects... I'd make changes myself, but I don't actually know enough about brown dwarfs! --Xanthine 08:33, 6 September 2006 (UTC)

I believe there is actually dispute about whether or not brown dwarfs (objects which fuse deuterium but not standard hydrogen) are stars or not, which most scientists disagreeing. However, there isn't such a thing as an object between a planet and a brown dwarf. If its smaller than a brown dwarf and orbits a "star or stellar remnant" its a planet. If its smaller than a brown dwarf and doesn't orbit a "star or stellar remnant its a sub-brown dwarf. This should be fixed. The Enlightened 11:48, 17 April 2007 (UTC)

Its been a while since I've read anything on brown dwarfs, but as far as I know, the dispute is as follows. Anything with a mass of less that about 0.08 solar masses is not a star. Period. A star is an object that fuses (or fused) hydrogen in its core. All objects with masses below this limit are substellar objects. Since substellar objects, in theory, have no lower mass limit, the tricky part is deciding when to call them planets or a brown dwarfs. There are two ways to divide this, by formation mechanism and by mass. The mass argument is that anything above about 12 Jupiter masses (note that Jupiter has a mass of 0.001 solar masses) is a brown dwarf since it can fuse deuterium and anything below this is a planet. Dividing by formation says that brown dwarfs form like stars, through the collapse of a cloud of gas, and planets form via the accretion of material that is in orbit around a star. Regarding the use of 'sub-brown dwarf' in the comment above, a search of the astronomy article database shows 7 papers written by three different authors that use the term 'sub-brown dwarf.' It seems as though this is being used to separate substellar objects above and below 12 Jupiter masses in to brown dwarfs and sub-brown dwarfs, respectively, due to the deuterium burning limit. This term is not common is astronomy, I assume because of the current discussion in defining planet vs. brown dwarf. One other point regarding the above comment. Location of the observed object has only a minor influence in how it is named since brown dwarfs are often found in multiple star systems (the first brown dwarf discovered, Gliese 229b, is in orbit around another star) and planets can easily be kicked out of orbit around their host star. Grochol17 (talk) 20:57, 19 November 2007 (UTC)

Graphics

The "Image:Sun Life.png" is really cool, can someone make a similar diagram for other stars with differing initial mass? --71.3.236.196 15:05, 9 September 2006 (UTC)

Like a comparison between red dwarfs, yellow dwarfs, etc? I would gladly, provided I have the spare time. :)

--Xanthine 16:45, 11 September 2006 (UTC)

Would this illustration be of use in this article?

Image:Stellar evolution L vs T.png

It's similar to, but not the same as, Image:Stellar evolution sun.svg. Thanks. — RJH (talk) 17:32, 20 December 2006 (UTC)

I think that figure's superb. BSVulturis 20:36, 17 January 2007 (UTC)

The image "The onion-like layers of a massive, evolved star just prior to core collapse" is very nice. However, on it the Neon-layer and the Oxygen-layer should swap. This is because the Neon is heavier then the Oxygen. —Preceding unsigned comment added by 161.209.206.1 (talk) 22:43, 18 March 2008 (UTC)

Data dump

From here Red Giant Branch stars: the theoretical framework to here:

< 0.075	⇒ brown dwarf
0.075 ... 0.4 M☉	⇒ red dwarf ⇒ black dwarf ??
0.4 ... 2.0 M☉	⇒ A, F, G, K, M core burners
	⇒ SGB subgiant	¹)
	⇒ SGB subgiant	²)
	⇒ first dredge-up	³)
	⇒ SGB subgiant	⁴)
	⇒ RGB giant	⁵)
	⇒ RGB-bump	⁶)
	⇒ RGB giant	⁷)
	⇒ TRGB/He-flash	⁸)
	⇒ ZAHB	⁹)
	⇒ HB (Red Clump)
	⇒ AGB giant
2.0 ... 4 M☉	⇒ B, A

¹)	thick H-shell burning, inert He-rich core, convective surface progressively deepening,
²)	the H-shell progressively narrowing, convective surface continually deepening,
³)	the convective surface reaches the inert He-rich core, and so mixes this with the atmosphere, the star instantaneously changes spectral profile, increased He and N:C proportions increases to CNO cycle equilibrium,
⁴)	convection deepens to base of RGB, then recedes
⁵)	thin H-shell burning and moving outwards, core degeneracy
⁶)	the H-shell reaches the base of the maximum convection extent, which is a chemical discontinuity, much richer H-fuel becomes available, and the star temporarily stops climbing the RGB,
⁷)	thin H-shell burning, core degeneracy, accelerating mass loss about 0.2 M☉,
⁸)	the He-core ignites and the He-flash thermal runaway ensues, the core expands and the degeneracy is diminished, sudden core convection sets in.
	★ neutrino losses from the degenerate core puts the max core temperature outside the centre, so the He-flash starts in a sphere, (my guess: inflating the core like a ballon)
	★ In some very metal poor stars, the He-flash may mix the core with the envelope, resulting in a H-flash, and a sudden enrichment of the atmosphere with He and C.
⁹)	Zero Age Horizontal Branch

Said: Rursus ☻ 10:56, 15 August 2007 (UTC)

redirected from

Not sure how to or I would do it myself, but when a person searches wiki for Stellar Remnant. As one might when taking an astronomy class. It should take them here. If someone knows how please share with me so I can learn. Viperix 03:16, 19 September 2007 (UTC)

Redirecting is fairly simple.

• First, you type the phrase into the search engine.
• You'll get a page saying that Wikipedia doesn't have a page about it.
• But there will be a redlink asking you to "create this page"
• So click it.
• On that page write REDIRECT# and then the link to the article. If you want to link to a section (as you would here) write "Article name#Section name."
• That should do it.
• However, in this case, it seems Stellar remnant already has a redirect, to compact star.

Serendi^podous 05:20, 19 September 2007 (UTC)

Thanks, I actually figured it out and came here to do it, but your right, it is redirected already. Viperix 07:53, 2 October 2007 (UTC)

So which is it?

The article says that the lifespan depends on the mass of the star. Uhh, well then say which is which. Will it live longer if it's more massive or less massive? Malamockq (talk) 23:49, 16 January 2008 (UTC)

Very roughly speaking, the lifespan of a star is proportional to the inverse-cube of the mass; which is to say, a star twice as massive will live 1/8 as long. Fig (talk) 15:14, 17 January 2008 (UTC)

I think it might be useful for the article to include something on this, along with some rough timescales ("A star of n solar masses would live for around x Myr"). Anyone else agree? Olaf Davis | Talk 11:34, 7 April 2008 (UTC)

Everybody agree. ... said: Rursus (^mbork³) 21:25, 14 December 2009 (UTC)

Stellar Remnants--A Fourth Possibility?

The "Stellar Remnants" section lists three possibilities for the end of a star: white dwarf, neutron star, or black hole. But isn't there a fourth possibility, namely, nothing? Frank Shu's textbook "The Physical Universe: An Introduction to Astronomy" [University Science Books, Mill Valley, CA, pp. 125-6, 1982—yes, I know this is old] says, "if the final explosion [of a star] is sufficiently violent, all the matter may be dispersed effectively into interstellar space." Thus, Shu lists four possibilities. JKW (talk) 01:53, 26 March 2008 (UTC)

• Sure, it is believed that Type 1a supernovae don't leave any compact remnants behind... --Etacar11 02:41, 26 March 2008 (UTC)

Hydrogen Supply

I haven't been able to find how much of a star's hydrogen is normally consumed before it's availability isn't large enough to make the PPI chain probable. Everywhere authors make statemets (like this article) that the hydrogen supply "runs out" but it obviously doesn't mean that there's no more hydrogen, it's simply not as available to make the chain probable since (for example) our Sun is a second generation star, meaning that a previous (or several previous) star(s) "consumed" their hydrogen supply before expelling their mass out into space, but still left plenty hydrogen for our beloved sun to still form and fuse Hydrogen. Can anyone please point me to how much hydrogen is left (percentage-wise if possible) when a star (like our own if necessary) "exhausts it's hydrogen supply"?. If possible email me about it (I don't know if I'll be able to watch this page) JunCTionS 05:16, 10 April 2008 (UTC)

Important to remember is that for all but the lowest-mass stars, the star is not well mixed. Consequently the hydrogen fraction is a function of radius in the star. What matters most for evolution is what the hydrogen fraction is at those areas which are hot enough for PPI (and other hydrogen-burning reactions) to operate. "Running out of hydrogen" means the hydrogen has been reduced to zero or near-zero abundance in the core, where the density & temperature are high enough for hydrogen fusion. The hydrogen content of the envelope is largely unchanged at the end of the main sequence, and the envelope is a larger mass fraction than the core, so a relatively small portion of the star's initial hydrogen mass has been consumed. The fraction which is consumed depends on initial mass, composition, rotation, etc. There are some diagrams in the technical literature of the internal composition at various times for a few sample cases, and from those diagrams you could do the sums and add up how much of hydrogen is consumed, but in terms of overall hydrogen consumed, I don't know that that is presented by itself anywhere. I'll try to run down references for you. BSVulturis (talk) 15:48, 20 May 2008 (UTC)

Also worth pointing out that although the sun is a "2nd generation" star (with high metallicity) it could still have been born from a molecular cloud of largely primordial hydrogen; but where the cloud itself has been enriched by secondary gas with high metallicity content. Fig (talk) 12:25, 22 May 2008 (UTC)

Though ... since there is no process now that creates hydrogen on a large scale ... it is generally true that all hydrogen is primordial, unprocessed since the Big Bang. BSVulturis (talk) 16:05, 16 June 2008 (UTC)

The replies had gone unnoticed until now. Thanks for your answers, quite clarifying. Have you had luck finding some sources?. Also, is there such a difference between core and envelope in which material (particulary hydrogen) isn't commonly exchanged?. Does the fact that hydrogen is the lightest ion here play a significant role in this?(I imagine the fluid mechanics here are quite different from the day-to-day where the denser materials sink, but it's a possibility) JunCTionS 23:35, 5 July 2008 (UTC)

Page Formatting

This page has quite a bit of useful information on it but it can be a bit difficult to distinguish the different stages of stellar evolution. Currently the main sequence is combined with end stages of a stars life cycle and the main sequence is barely mentioned at all. I propose that star formation, main sequence and late stages should be put under their own individual headings and some estimates of the length of each of each of these stages for different sized stars to give the reader a better overview of the cycle from start to finish.Coffeeassured (talk) 06:01, 15 April 2008 (UTC)

About the Star Birth Section

I think it should be mentioned whether this (the birth of a star) has been witnessed or not. And if indeed the birth of a star has been witnessed an example should be given. It would be a bit more complete that way, I think. KeshethEl (talk) 11:18, 10 May 2008 (UTC)

The Validity of this Article's Assumptions

I see many assumptions of this article, and I would like the author to argue for the validity of the article. This is my opening argument: How and Why do we think that there are stars forming?69.23.146.251 (talk) 22:48, 20 June 2008 (UTC)Westivoja

Across the galaxy, we find many stars in different stages of their life cycle, from just after birth to advanced old age and after death. There are a number of methods for determining the ages of stars, and younger stars tend to behave in a certain way, and older stars tend to behave in a different way. As for dead stars, we lucked out in 1054. In that year a supernova was recorded by the Chinese, and its precise location in the sky was given in charts. Today, that location houses the crab nebula and has a rapidly rotating pulsar at its centre. Serendi^podous 07:10, 21 June 2008 (UTC)

Just because we see them change doesn't mean that they evolved. Ever heared of Boil's Gas Law?69.23.146.251 (talk) 16:26, 21 June 2008 (UTC)Westivoja

The claim that stars don't evolve is wildly outside mainstream physics and astronomy; any introductory astronomy textbook discusses the widely accepted stellar evolution models in detail. A different point of view would require a number of reliable sources. ASHill (talk | contribs) 17:05, 23 June 2008 (UTC)

• Something about this anon's comments screams "Young Earth Creationist" to me. Apologies to him/her if I'm jumping to the wrong conclusion... --Etacar11 17:48, 23 June 2008 (UTC)

I'm dissapointed you did not answer the question. Please tell me how to overcome Boil's Gas Law, a 100% scientific law. Please tell me how to overcome a LAW. 69.23.144.2 (talk) 21:02, 23 July 2008 (UTC) Westivoja—Preceding unsigned comment added by 69.23.144.2 (talk) 20:59, 23 July 2008 (UTC) By the way, I am a Young Universe Creationist. Please visit http://www.geocities.com/paulindab/evocreo for info on that. But we are discussing Stellar Evolution, the third stage of evolution.69.23.144.2 (talk) 21:06, 23 July 2008 (UTC)Westivoja

If you want to be taken seriously, you should learn to spell correctly. It is "Boyle's Law", not "Boil's Law". Also, this talk page is to be used only for discussing improvements to the article. Wikipedia is not a forum. If you want to argue about the merits of evolution vs creationism, please do so at another venue. J.delanoy^gabs_adds 21:10, 23 July 2008 (UTC)

Thank You for correcting me on the spelling. But, did I ever say we were discussing creation, and evolutionism?69.23.144.2 (talk) 22:09, 23 July 2008 (UTC)Westivoja

Scientific "laws" are just observations about what always happens under certain conditions. Boyle's law applies only to a gas at a fixed temperature, not to the universe.
The word "evolution" means "a process of gradual change" (OED) and is observed in inferred from observations of stars. This has no direct connection with "evolutionism". Dbfirs 22:25, 23 July 2008 (UTC)

And when trying to squeeze gas together to make a star their would be a fixed tempeture therefore driving the gas away from each other. As for evolutionism and creationism thing you were talking about, I don't think it's something worth arguing about.69.23.144.2 (talk) 16:28, 24 July 2008 (UTC)Westivoja

As User:J.delanoy mentioned, Wikipedia is not a place to debate the science; we should only discuss verifiable improvements to the article. —Alex (ASHill | talk | contribs) 16:43, 24 July 2008 (UTC)

Well, then we should conclude stellar evolution is unscientific. Thank you for discussing it with me.69.23.144.2 (talk) 17:48, 24 July 2008 (UTC)Westivoja

Cloud of gas to star ... constant temperature? Have you read the article? Dbfirs 07:02, 5 August 2008 (UTC)

User 69.23.144.2 shouldn't discuss the validity of science in this talk page. This talk page is dedicated to whether the article stellar evolution is well written or not, according to science, whether valid or not. When making post here, one have to assume or imagine that the underlying science is correct. Discussing it here is wasting bandwidth. ... said: Rursus (^mbork³) 21:35, 14 December 2009 (UTC)

Link dump

• Low-mass stars: pre-main sequence evolution and nucleosynthesis by Forestini, M.

... said: Rursus (^mbork³) 21:35, 14 December 2009 (UTC)

References

This page has almost no references to back up most of the information presented (only 13 references with over 35 paragraphs, most of which introduce new data/concepts). Without the references, this may as well be classed as original research. 203.219.66.57 (talk) 14:16, 10 January 2010 (UTC)

Stellar Evolution is not science

This article which shows evolution of stars ,their life cycle and death is mere imagination.There is not scientifically proven theory to what is being explained.The explanation is a mere process which has no science in it.They just seem to discribe what they have seen in the images of stars.It is just a discription.This discription does not follow laws of Light travelling through the space neither it gives any scientific reasoning to what causes such an immense gravity that a star keeps shrinking.And how can anything explode that so perfectly leaving a good circular hole in the centre.There is no such theory which can prove that when an explosion takes place the outer part remains intact.What kind of Stellar evolution and what kind of scientific theory are they talking about.Its just not science! --Wizziwizard (talk) 14:55, 22 January 2010 (UTC)

Well, the people who came up with these theories and spend their lives improving them would disagree. If you've read their work and believe you can prove it wrong, I suggest contacting an appropriate astronomical journal and seeking publication. However, Wikipedia is a 'tertiary source' which means that we report on and summarise the current scientific consensus. It's not our job to decide whether the experts are right or wrong but to report what they say, so a discussion of such is not really suited to this talk page. Olaf Davis (talk) 15:50, 22 January 2010 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Stellar evolution/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Well written article, but it needs more citations. However, it may already qualify as a good article. ==Quantitative timeline data missing== A glaring omission, in an article on this subject, is the complete and total lack of quantitative data on stellar lifetimes. There is a picture of the Sun's life cycle, marked off in billions of years--and that's it. As a minimum, I would expect a diagram of lifetime vs. mass for main sequence stars. How long does a class A star stay on the main sequence? A class F? A class K? This is the article that ought to address such questions, but it does not. Freederick (talk) 15:04, 20 July 2010 (UTC)

Last edited at 15:04, 20 July 2010 (UTC). Substituted at 15:52, 1 May 2016 (UTC)