Talk:Chandrasekhar limit/Archive 1

Archive 1

Origin of Mass limit

While known as Chandrasekhar limit, there is work on white dwarf mass limits that predates Chandrasekhar, namely Wilhelm Anderson of Tartu University and Edmund Clifton Stoner of Leeds University - see also NATURE|Vol 440|9 March 2006 p148: "Giants of physics found white-dwarf mass limits"

Usage of a phrase

"The limit was first discovered and calculated by the Indian physicist Subrahmanyan Chandrasekhar in 1930, during his maiden voyage to Britain from India."

I've never seen the term "maiden voyage" applied to anything but a boat/ship; certainly not a person (or a male, for that matter!) Anyone have direct or specific knowledge regarding the usage of this phrase?

Heat or radiation?

"The heat generated by a star pushes the atmosphere of the star out." I always thought it was mainly radiation that supports stars?

Technically it is radiation pressure* that prevents a star from collapsing under gravity but I think 'heat' is being used here as thermal radiation. *Radiation pressure being the actual pressure exerted outwards by the photons generated during the nuclear fusion. Joanna Goodger 15:04, 24 January 2006 (UTC)

this is only partly correct. What stops a star collapsing under gravity is when the rate of change of total pressure with respect to radius exactly balances the density times the gravitational force - the equation of hydrostatic equilibrium (see stellar structure). The radiation pressure is only one part of the total pressure. It's important in really big stars but for instance in the sun's core the radiation pressure only makes a tiny contribution to the total pressure. The other major contribution is from the ideal gas pressure, which itself is related to the temperature, which is affected by the energy generated by nuclear reactions. I believe this provides most of the pressure gradient; without the fusion process going on there wouldn't be hydrostatic equilibrium, the star would just be contracting with an acceleration term given by the difference between the pressure gradient and the gravity times density. There are other contributions to the pressure in more sophisticated stellar models, such as the electron degeneracy pressure. Of course, fusion changes the chemical composition of the star so it isn't in perfect equilibrium, but it slows the collapse by a big factor. For instance the sun would collapse in about 10 million (10⁷) years without the core hydrogen fusion contributing to the pressure gradient, but happily for us its core hydrogen-burning lifetime is about 10 billion (10¹⁰) years. Thus fusion slows the contraction down by a factor of about one thousand. Puzl bustr (talk) 21:12, 29 October 2009 (UTC)

The reference for my discussion above is An Introduction to Modern Stellar Astrophysics, 2nd ed, by Dale A. Ostlie and Bradley W. Carrol. To clarify, the fusion processes are modelled with another equation, the luminosity gradient equation, saying the luminosity gradient is 4 pi times the radius squared times the density times epsilon, where epsilon is the total energy released per second by all nuclear reactions and by gravity. Again see stellar structure. The reason the radiation pressure is so small in the sun's core is that the temperature is relatively low, yet the energy of the photons released by hydrogen fusion, as in the previous comment, is very high. In other words, the radiation pressure is due to the thermal energy, where the photons are relatively low energy, but the photons produced by fusion are high energy. It's just that the way the physics is modelled, the fusion gets treated in the luminosity gradient equation. Its a bit mind-bending, but remember that most of these variables, like pressure, temperature and density, are all related, not independent.Puzl bustr (talk) 21:49, 29 October 2009 (UTC)

"ergs"?? "dynes"?? As a product of 1960's and 1970's Mechanical Engineering education at the Universities of Illinois and Florida, having turned to Nuclear Physics in the 1980's at FSU, and now being a teacher of Physics....I have come to appreciate the SI system (the modern version of the metric system, now used by most countries in the world)....please use it in your documents! Thanks!198.146.57.2 14:51, 27 July 2006 (UTC)

Misconceptions regarding white dwarf collapse

I have corrected several misconceptions regarding white dwarf collapse, namely:

The old idea that white dwarfs which have reached the Chandrasekhar limit and started to collapse are the progenitors of Type Ia supernovae, was superseded in the 1960s by the theory that runaway nuclear fusion is triggered by increasing interior density in carbon-oxygen white dwarfs prior to their attaining this limit.

The hypothesis that white dwarfs collapse into neutron stars during the course of a Type Ia supernova explosion is now regarded as being incorrect; neutron stars can be formed in Types Ib, Ic, or II supernovae (whose progenitors are far more massive than white dwarfs - over about 12 solar masses: they are called "massive stars" whereas the white dwarfs whose lives end in type 1a supernovae are about 1.4 solar masses), but most astrophysists now believe that in a Ia supernova the white dwarf is obliterated, leaving nothing behind except the plasma and radiation of the supernova remnant.

This is probably true, but it (and everything else on Wikipedia) needs a citation added. Also, please sign your postings to the talk page by adding ~~~~ to the end of your post. Richard B 18:55, 4 November 2006 (UTC)

Controversy on Chandrasekhar - Eddington relations

In a review of Arthurs I. Miller's biography of Subrahmanyan Chandrasekhar published in Physics Today (feb 2006, p.53) Kameshwar Wali shows sharp disagreement with the point of view expressed by Miller as regards the relations between Chandra and Eddington, and the attitude of the later and other Oxbridge astrophysicists towards Chandra's white dwarf theory, based on his own numerous and extensive conversations with Chandrasekhar that furnished him with the material for Chandra's biography that Wali himself wrote about fifteen years ago. To a collegue in India that he wanted to persuade to come and visit Cambridge, Chandra wrote, among other: " In Cambridge I get the utmost sympathy and encouragement for my work. Fowler, Eddington and Dirac are all extremely kind and encouraging and even spend quite considerable time to clear up some difficulties that I may come across." So the least that can be said is that the case needs further study before being filed in the catalogue of histories about sectarist, not to say racist, attitudes of european scientists towards an indian colleague in those times.—Preceding unsigned comment added by 134.158.154.30 (talk • contribs) 13:12, 26 September 2006

Jayen's comment
What would one expect a guy to say?
Havent we heard of the Stockholm syndrome, where the victim begins to "forcibly like" the perpetrators? His career would be at stake if even a single word got out about "cribbing" or "protest"!
Come on!!
defenders of racism are always plenty! Some even propagating the view that negroes loved being exploited by the europeans, the american indians wanted white guys to throw them out of their own lands and that they never amounted to anything anyway!!
But actions speak louder than words!
The fact that he got a well deserved Nobel prize SO LATE speaks volumes for European/white attitude?

Try imagining a british/french/scandinavian (oh so white and propah) guy coming up with Chandra's ideas?
He would have been feted round the world and even if he WAS mad and dangerous, (beautiful mind), have got a nobel promptly.
Why! there would even have been a movie or two to boot!
Just so the "rest of the world" got to know how beautiful & wonderful the "white mind" was!!
Jayen —Preceding unsigned comment added by 195.229.115.202 (talk • contribs) 08:04, 11 June 2008

Wrong formula

Surely it can't be correct to express the limiting mass as the sum of the Sun's mass and the formula. The only way something like that could arise would be as a part of an expansion around the solar mass, which there is no indiaction of here. Is the "+" supposed to be multiplication instead? The article itself makes use of the +, though, using it to derive a limiting mass for a neutron white dwarf of one solar mass. It is hard to see how a star with no electrons could be supported by electron degenerace pressure. I don't have the correct formula at hand, but this needs to be fixed. Oh, and the "definition" given as an approximate equation in the beginning should also be fixed. Amaurea 15:48, 20 November 2006 (UTC)

I'm having trouble figuring out why this formula is considered important, as it applies to an object likely to be nearly non-existent - a non-rotating white dwarf. When's the last time we saw a non-rotating star? Jamey Fletcher 74.178.120.235 (talk) 20:38, 23 March 2010 (UTC)

For me its is important because it provides the G-dependence of the Chandrasekhar Mass Limit. In the Hypergeometrical Universe Theory Gravitation is epoch-dependent and velocity-dependent.

This means that type 1A Supernova becomes epoch dependent in HU. correcting the photometrically derived SN1a distances in SN1a Survey Union 2.1 leads to perfect HU parameterless predictions:

Parameterless predictions of SN1a Supernovae distances

— Preceding unsigned comment added by Ny2292000 (talk • contribs) 15:40, 11 November 2017 (UTC)

Value given

The mass value is given in this article as "about 1.4 solar masses" but is given in the Supernova article as "roughly 1.38 times the mass of the sun" and the IK Pegasi article as "1.44 solar masses". I know there may be controversy over the value, but it might be best to settle on a single figure (or approximation) and a citation and give it consistently throughout these articles. Kantokano (talk) 10:15, 17 October 2008 (UTC)

That would be nice - and wrong. As long as we haven't observed even one single SN Ia progenitor we have no certain knowledge of their composition - average wd or special - or whether there is a range or one single value for their mass. The actual limit is guided solely by the proportion of protons to neutrons. John.St (talk) 05:36, 29 December 2008 (UTC)

How does the exclusion principle actually fail?

If the Pauli exclusion principle is a law of nature, why does it fail above a certain mass? So multiple neutrons cannot occupy the same quantum state... unless you push them really hard together. I'm not educated in this domain, but I don't understand how this is possible. —Preceding unsigned comment added by 91.176.240.6 (talk) 16:33, 4 October 2009 (UTC)

It doesn't fail. There just happens to be a maximum mass for which the core could be supported by electron degeneracy pressure, because this pressure has a maximum value, as indicated in the article. If the mass goes beyond this value, the gravity due to the mass is too powerful for the electron degeneracy pressure (strictly, the rate of change of total pressure with respect to the radius) to counterbalance it and keep the core in hydrostatic equilibrium. Chandra showed that there was a maximum mass for a white dwarf. What happens at a greater mass is simply that the core collapses further under gravity. The electrons being as closely packed as they could be already, the only way for this to be possible, which I agree is confusing on first glance, is for the electrons to cease to be free and instead combine with the protons in the nuclei to make neutrons, plus neutrinos, by a process called inverse beta decay, as described in core-collapse supernova. Getting rid of the electrons this way then allows the core to continue to collapse to nuclear densities. The point is that one can no longer talk about a white dwarf when this happens as a white dwarf has a free electron plasma. The Pauli principle no longer applies to the electrons because they have gone!! This doesn't violate any laws of physics since the neutrinos escaped from the core - they were the electron counterparts but since they interact so weakly with matter and travel at virtually the speed of light they speed right out of the core usually without a single interaction. OK, later on in the collapse, as the core approaches nuclear densities, any neutrinos may have an interaction or two before escaping, but that's another question. The Pauli principle applies to fermions, including electrons, protons and neutrons, but it so happens that the protons and neutrons aren't yet degenerate at the density when the electrons are degenerate, so getting rid of the electrons is all that is needed. In fact, the Pauli principle become important again at even higher densities, when this time it applies to the neutrons (the protons having also gone by being combined with the electrons). The neutron degeneracy pressure may be able to stop the core collapse, resulting in a supernova and a neutron star, or if the mass is still too great, you get the really whacky stuff - formation of a black hole, which I'm not going to try to explain:). Except that, by analogy with what I said above for the electrons, to get around the neutron degeneracy pressure you'd just not have to have neutrons any more. One theory about that is that you can get a quark plasma, where the quarks are the constituents of the neutrons. So effectively you've broken the neutrons apart into quarks, which presumably allows even further collapse and maybe quark degeneracy pressure (OK, I admit this is beginning to sound like turtles all the way down :)). Each successive collapse is raising the temperature and density to incredible (astronomical is now too weak a term;)) levels; with enough energy just about any particles can be broken apart. Puzl bustr (talk) 20:44, 29 October 2009 (UTC)

Maybe the article should mention the inverse beta decay? But leave out the turtles... Puzl bustr (talk) 20:51, 29 October 2009 (UTC)

My mistake. The article does mention the protons turning to neutrons in the Applications section, without explicitly mentioning inverse beta decay, so I put that in.Puzl bustr (talk) 21:23, 29 October 2009 (UTC)

de-linked David R. Branch

Not able to find anything more notable about David R. Branch online than that he is 'an astronomer at the University of Oklahoma'. I removed the red link to his name, instead simply describing him as indicated. If someone wants to write a biography article about him, they can overturn this edit.Puzl bustr (talk) 20:04, 29 October 2009 (UTC)

Jargon

I made an attempt at clearing up the jargon in the introductory section. I liked what it had to say, but I rewrote some of it to emphasize the connection to white dwarfs and to try to make it a little clearer to readers without an astronomy background. The short paragraph on stellar evolution I moved to the beginning of the Physics section as I thought it might be more appropriate there. In the interest of neatness I created bullet points to describe the variables in Chandrasekhar's equation. I removed a short line of algebra below, which I thought was a little redundant. In my rewrite I left out the emphasis on non-rotation, although I admit it is an assumption made in the derivation with possible physical consequences as mentioned in the Champagne Supernova section. It's not perfect but I hope it is a step in the right direction.--Braincricket (talk) 04:41, 25 January 2011 (UTC)