View source for Talk:White dwarf

{{ArticleHistory
|action1=GAN
|action1date=03:10, 22 June 2007
|action1result=listed
|action1oldid=139814207

|action2=FAC
|action2date=17:10, 24 September 2007
|action2link=Wikipedia:Featured article candidates/White dwarf
|action2result=promoted
|action2oldid=159635883

|maindate=June 25, 2009
|maindate2=June 24, 2025
|currentstatus=FA
|topic=Natsci
|action3 = FAR
|action3date = 2025-01-25
|action3link = Wikipedia:Featured article review/White dwarf/archive1
|action3result = kept
|action3oldid = 1271696658
}}
{{Talkheader}}
{{WikiProject banner shell|class=FA|vital=yes|1=
{{WikiProject Physics|importance=High}}
{{WikiProject Astronomy|object=yes|importance=top}}
}}
{{annual readership}}
{{Archive box|auto=long|age=90|bot=Lowercase sigmabot III}}
{{User:MiszaBot/config
|archiveheader = {{talkarchivenav|noredlinks=y}}
|maxarchivesize = 100K
|counter = 1
|algo = old(90d)
|archive = Talk:White dwarf/Archive %(counter)d
}}

== Computational relations for white dwarfs ==

Given a mass (M/M๏) and an effective temperature (T), it is possible to determine the radius (R/R๏), the luminosity (L/L๏), and the age (t) for a carbon-oxygen core white dwarf.

The two quadratic equations and the line below comprise a good curve-fit for the white dwarf mass-radius relation from 0.25 to 1.41 solar masses.

If 0.25 ≤ M/M๏ < 0.45, then

R/R๏ = 0.07279307 (M/M๏)² − 0.0752974 (M/M๏) + 0.03327478

If 0.45 ≤ M/M๏ ≤ 1.2, then

R/R๏ = −0.010421 (M/M๏) + 0.018821

If 1.2 < M/M๏ ≤ 1.41, then

R/R๏ = −0.0814246 (M/M๏)² + 0.1899852 (M/M๏) − 0.1044496

Next, the luminosity of the white dwarf is found from the Stefan-Boltzmann law.

T๏ = 5784K

L/L๏ = (R/R๏)² (T/T๏)⁴

Finally, the age of the white dwarf, t, in years.

t = 10^[6.7 − (5/7) log(L/L๏)]

Observed white dwarf color temperatures are slightly affected by the gravitational red shift, which can be corrected spectroscopically. Also, if the apparent magnitude and the parallax (distance) of the white dwarf are accurately determined, the luminosity can be calculated without reference to the temperature.

It has been asked whether white dwarfs could be used as suns for artificial colonies in space. The answer is yes, barely. The problem is that the distance at which an orbiting space station would receive the same intensity of radiation that the Earth gets from the sun is usually very close to, or even within, the Roche limit of the white dwarf with respect to the space station (nominally assumed to have an average density of 100 kg m⁻³).

Beginning with the Stefan-Boltzman law again, and making the necessary substitutions, while assuming a subsolar temperature equal to that of Earth (393.6K), we find the nominal distance of the habitable zone:

rᵤ = 48977 t^(−0.7)

And for the Roche limit:

rᵥ = (5.22495e-12 AU/m) (M/ρᵥ)^(1/3)

where ρᵥ is the effective density of the space station, in kg m⁻³. M is the white dwarf's mass in kilograms. However, rᵥ and rᵤ are both returned in astronomical units.

An 0.5 solar mass white dwarf having an effective temperature of 6000K will have a radius of 0.0136105 solar radii, a luminosity of 2.1451e-4 L๏, and an age of 2.0912 billion years. It's habitable radius will be 0.014646 AU. It's Roche limit with respect to a (ρᵥ = 100 kg m⁻³) space station will be 0.011236 AU.

Most white dwarfs will be too massive or too old (i.e., too cool) for the habitable zone to exist in the conventional sense because it would occur inside the Roche limit.

== Coronae ==

A new section was added called "Coronae". The content is based on an uncited 2024 primary reference. My summary of this content is "No  coronae have been found."  This is not knowledge but a non-progress report.
 
In my opinion the reference and the content fall below the bar for a Featured Article. I would like to hear why this content should be added.
@[[User:Termynaytor|Termynaytor]] can you help me understand your reasoning? [[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 01:55, 21 December 2024 (UTC)

: The lack of this feature is still of interest, at least to me. But the section is a stub and I think it should be merged into the "Atmosphere and spectra" section. Cf. [[WP:OVERSECTION]]. [[User:Praemonitus|Praemonitus]] ([[User talk:Praemonitus|talk]]) 03:46, 21 December 2024 (UTC)
::+1. I don't see a need for a coronae section. <span style="font-family:Times New Roman;font-size:100%;color:#00008B;background-color:transparent;;CSS">[[User:Zzzs|<sub>Z</sub>Z<sup>Z</sup>]][[User talk:Zzzs|'S]]</span> 04:07, 21 December 2024 (UTC)

:I think it is a perfectly good and valid piece of information to add to the article.[[User:Termynaytor|Termynaytor]] ([[User talk:Termynaytor|talk]]) 07:20, 21 December 2024 (UTC)
::Do you have a reason? <span style="font-family:Times New Roman;font-size:100%;color:#00008B;background-color:transparent;;CSS">[[User:Zzzs|<sub>Z</sub>Z<sup>Z</sup>]][[User talk:Zzzs|'S]]</span> 14:23, 21 December 2024 (UTC)
::: There are several studies on the subject.[https://ui.adsabs.harvard.edu/abs/1976A%26A....50..319H/abstract][https://ui.adsabs.harvard.edu/abs/2007ApJ...657.1026W/abstract][https://ui.adsabs.harvard.edu/abs/2004ARep...48..121Z/abstract][https://ui.adsabs.harvard.edu/abs/2005ApJ...625..973D/abstract] The topic appears notable and I think it should be mentioned in this article. [[User:Praemonitus|Praemonitus]] ([[User talk:Praemonitus|talk]]) 16:01, 21 December 2024 (UTC)
::::I misinterpreted their question to be supportive of an independent section just of the coronae. I'm completely fine with the inclusion of the information, just not in its own section. <span style="font-family:Times New Roman;font-size:100%;color:#00008B;background-color:transparent;;CSS">[[User:Zzzs|<sub>Z</sub>Z<sup>Z</sup>]][[User talk:Zzzs|'S]]</span> 16:00, 21 December 2024 (UTC)
::::@[[User:Praemonitus|Praemonitus]] I have no principle objection to content based on such sources. I only object to the actual content added and its reference. [[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 17:15, 21 December 2024 (UTC)
:Sorry I guess my wording created confusion. I have no objection to reliably sourced content about coronae, either in a section or not. I object to adding this marginally sourced content about non-observation to an FA article.  According to the content:
:* "so far, searches for white dwarf coronae at X-ray and radio wavelengths, where coronae are most easily detected, have failed to detect any."
:This is not encyclopedic knowledge. The coronae are not a linchpin in an important theory. In fact only one non-notable person claims they might exist according to the content. They might be found by looking elsewhere or by other means. The content and the ref are below the bar. [[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 17:13, 21 December 2024 (UTC)
:: Okay. Well the inability to detect something predicted can be in and of itself interesting and notable. Just look at dark matter. There have been searches for white dwarf coronae and those failures are meaningful. "Several theorists (e.g., Zheleznyakov & Litvinchuk 1984; Serber 1990; Thomas et al. 1995) have suggested that single, cool, magnetic white dwarfs might have coronae."[https://iopscience.iop.org/article/10.1086/510776/pdf] [[User:Praemonitus|Praemonitus]] ([[User talk:Praemonitus|talk]]) 18:02, 21 December 2024 (UTC)
:::I changed the content using the ref you provided. [[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 20:18, 21 December 2024 (UTC)
: Sure, I can add some background.  Firstly, it is unfortunate that the revision has degraded the information presented.  It may come as a surprise to many that a class of stars appears to lack coronae, which are otherwise commonplace among stars.  This has implications for the transmission of energy from the convective envelope (where they exist among white dwarfs).  By the way, the topic about the absence or presence of convection in envelopes of white dwarfs is missing from the structure content and should be added.  Secondly, information pointing readers to the theoretical basis for coronae and their energetics among white dwarfs was deleted by one Johnjbarton.  This is a non-trivial topic, although it was assumed to be by some editors.  I recommend that the special section on coronae be restored in light of these considerations- and as I pointed out, unless someone is willing to add a subsection on convection in WD atmospheres and envelopes, perhaps leave it alone until they know something more?  Thirdly, we should also add subsections on recent theoretical work on dynamos in white dwarfs.  Thanks.[[User:TOSStheProtoss|TOSStheProtoss]] ([[User talk:TOSStheProtoss|talk]]) 03:25, 22 December 2024 (UTC)
::Re Firstly: the original content said "It is unknown whether white dwarfs have hot outermost layer of plasma called [[Stellar_corona|coronae]] like other classes of stars." but it was unsourced and nothing was said about implications. If you have sources on this and you think can be included go for it.
::Re Secondly: The original content said "Based on theoretical work conducted in the 1980s, Z. E. Musielak argued that some types of white dwarfs may have corona." and the current content says "While theoretical work suggests that some types of white dwarfs may have stellar corona," The claim about the 1980s was not in the source cited and other names were used. Thus I would claim that the current content is more correct according the source and nothing was deleted.
::I strongly support more well sourced content on white dwarf coronae! [[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 04:18, 22 December 2024 (UTC)
::: My suggestion is to add a few paragraphs on this subject to the "[[Stellar_corona#Stellar_coronae|Stellar coronae]]" section of the Stellar corona article. Once that is properly developed, it can be fed back into this article summary style. [[User:Praemonitus|Praemonitus]] ([[User talk:Praemonitus|talk]]) 15:16, 23 December 2024 (UTC)

== Mass–radius relationship ==

The section on "Mass–radius relationship" cites http://www.sciencebits.com/StellarEquipartition, but there is no equation like the first one in the wiki page on that site. The equation on the site is similar to the one on page 25 in {{cite book
 |last1=Kawaler |first1=S. D.
 |chapter=White Dwarf Stars
 |editor1-last=Kawaler |editor1-first=S. D.
 |editor2-last=Novikov |editor2-first=I.
 |editor3-last=Srinivasan |editor3-first=G.
 |date=1997
 |title=Stellar remnants
 |publisher=1997
 |isbn=978-3-540-61520-0
}} 
I will convert to the Kawaler form. [[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 20:38, 14 January 2025 (UTC)

== H-R Diagram Jargon ==
[[File:ESO - Hertzsprung-Russell Diagram (by).jpg|right|thumb|upright=1.8]]
The "Hertzprung-Russel Diagram" in the article has axes labled with unexplained jargon. I can't guess their relation (if any) to a normal H-R diagram's axes of absolute magnitude and temperature. I'm not even sure this ''is'' a Hertzprung Russel diagram. With jargon like that, the axes might as well not be labeled at all. Please either explain them clearly, in English words, or delete the useless diagram. [[Special:Contributions/2601:441:5000:13E0:2CDD:AF61:295A:17B1|2601:441:5000:13E0:2CDD:AF61:295A:17B1]] ([[User talk:2601:441:5000:13E0:2CDD:AF61:295A:17B1|talk]]) 02:56, 24 January 2025 (UTC)
:I worded that too harshly, sorry. But please, would someone who understands these equations please provide an English explanation in the caption? It's not necessary or fair to make physics articles on Wikipedia incomprehensible to non-doctorates. [[Special:Contributions/2601:441:5000:13E0:2CDD:AF61:295A:17B1|2601:441:5000:13E0:2CDD:AF61:295A:17B1]] ([[User talk:2601:441:5000:13E0:2CDD:AF61:295A:17B1|talk]]) 03:39, 24 January 2025 (UTC)
:: The labels are linked to articles on the terminology. I suppose it could use temperature and luminosity instead. [[User:Praemonitus|Praemonitus]] ([[User talk:Praemonitus|talk]]) 15:20, 24 January 2025 (UTC)
:::I think the OP is referring to a different diagram: see where the clarification needed tag is.  I'll add something in the caption that explains.  [[User:Lithopsian|Lithopsian]] ([[User talk:Lithopsian|talk]]) 15:27, 24 January 2025 (UTC)
:::: Mmm, the OP seems to be referring to a label printed on the chart, so I'm not so sure. The OP will need to clarify. Thanks. [[User:Praemonitus|Praemonitus]] ([[User talk:Praemonitus|talk]]) 15:44, 24 January 2025 (UTC)
:::: Thank you very much for explaining the axes, and for linking to G-Band and color index, Lithopsian. Now it's possible to tell how it relates to stellar HR diagrams. [[Special:Contributions/2601:441:5000:13E0:0:0:0:932F|2601:441:5000:13E0:0:0:0:932F]] ([[User talk:2601:441:5000:13E0:0:0:0:932F|talk]]) 03:16, 15 March 2025 (UTC)

== Delayed helium-core flash on the white-dwarf cooling curve ==

Apparently it is possible for some stars to undergo a delayed helium-core flash while a white dwarf. These stars undergo rapid mass loss, leaving the RGB to become white dwarfs that later flash ignite.[https://ui.adsabs.harvard.edu/abs/2004ApJ...602..342L/abstract] In this case, the first white dwarf stage doesn't represent the end of their evolution. [[User:Praemonitus|Praemonitus]] ([[User talk:Praemonitus|talk]]) 19:47, 24 January 2025 (UTC)
:White dwarf mergers are also thought to sometimes produce stars undergoing fusion.  R CrB variables and some HdC stars are candidates for the results of such mergers.  And obviously, mergers are possible progenitors of type Ia supernovae, not that those would be considered much of an ongoing life.  [[User:Lithopsian|Lithopsian]] ([[User talk:Lithopsian|talk]]) 20:35, 24 January 2025 (UTC)
:: I think these scenarios suggest that the 'Fate' section needs an update. The double degenerate scenario for Type Ia supernovae is already covered. [[User:Praemonitus|Praemonitus]] ([[User talk:Praemonitus|talk]]) 15:11, 26 January 2025 (UTC)
:: P.S. it looks like the topic is covered by the [[Extreme helium star]] article. [[User:Praemonitus|Praemonitus]] ([[User talk:Praemonitus|talk]])

== Neon-22 distillation ==

Here's another topic that probably should be covered by this article:
*{{cite journal
 | title=<sup>22</sup>Ne Phase Separation as a Solution to the Ultramassive White Dwarf Cooling Anomaly
 | last1=Blouin | first1=Simon | last2=Daligault | first2=Jérôme | last3=Saumon | first3=Didier 
 | journal=The Astrophysical Journal Letters
 | volume=911 | issue=1 | at=id. L5 | date=April 2021
 | doi=10.3847/2041-8213/abf14b | arxiv=2103.12892 
 | bibcode=2021ApJ...911L...5B }}
There are a number of papers available on Neon-22 Distillation, so the topic appears notable. [[User:Praemonitus|Praemonitus]] ([[User talk:Praemonitus|talk]]) 00:36, 4 February 2025 (UTC)
: Okay, I found the section where the white dwarf cooling anomaly is discussed. Never mind... [[User:Praemonitus|Praemonitus]] ([[User talk:Praemonitus|talk]]) 14:27, 5 February 2025 (UTC)