Talk:White dwarf

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.

I am reviewing this article as part of WP:URFA/2020, an initiative to evaluate older featured articles to ensure that they still meet the FA criteria. I have some concerns with this article:

• There are numerous uncited passages, including whole sections at the end of the article.
• The gallery at the end of the article should be evaluated. Can these been used in other sections of the article instead, or perhaps removed?
• There are references that need to be properly formatted, especially the last three. Has anyone checked to ensure that they are high-quality sources?

Is anyone intersted in fixing up the article? If not, I will nominate this to WP:FAR in a couple of weeks. Z1720 (talk) 15:10, 26 January 2024 (UTC)Reply

In revisiting this article, I see that some of the problems have been fixed, while other concerns still remain. There are some sections that are uncited and the gallery is still present even though Wikipedia is not a gallery. Is anyone willing to address these issues or should this go to WP:FAR? Z1720 (talk) 23:39, 16 November 2024 (UTC)Reply

The paragraph says that radiative heat transfer is low "because any absorption of a photon requires that an electron must transition to a higher empty state, which may not be possible as the energy of the photon may not be a match for the possible quantum states available to that electron" I don't think the lack of absorption is important, but the lack of emission is. If thermal radiation wouldbe emitted, the thermal energy would go somewhere. It would probably be absorbed in the outer layers, or be emitted, leading to fast cooling of the core. But I think in the same way as the lack of empty states prevents absorption, it is also preventing thermal excitation of electrons to energy levels from where they could emit radiation. Emilo Alberto (talk) 11:21, 8 March 2024 (UTC)Reply

The article on SN 1181 says:

With a temperature near 200,000 K, WD J005311 is among the hottest stars known. The extreme properties of the central star are being powered by the residual radioactive decay of ⁵⁶Ni, where the usual half-life of 6.0 days from electron capture is increased to many centuries due to the nickel being completely ionized.

This contradicts the present article, whose lead paragraph twice states that a white dwarf "has no source of energy"; the article doesn't mention that white dwarfs may be powered by radioactive decay. Joriki (talk) 07:55, 25 October 2024 (UTC)Reply

These entries in Further reading seem to be sources that did not make the cut to be included in the article, rather than deep sources for readers:

Variability

• Winget, D.E. (1998). "Asteroseismology of white dwarf stars". Journal of Physics: Condensed Matter. 10 (49): 11247–11261. Bibcode:1998JPCM...1011247W. doi:10.1088/0953-8984/10/49/014. S2CID 250749380.

Magnetic field

• Wickramasinghe, D. T.; Ferrario, Lilia (2000). "Magnetism in Isolated and Binary White Dwarfs". Publications of the Astronomical Society of the Pacific. 112 (773): 873–924. Bibcode:2000PASP..112..873W. doi:10.1086/316593.

Frequency

• Gibson, B. K.; Flynn, C (2001). "White Dwarfs and Dark Matter". Science. 292 (5525): 2211a. arXiv:astro-ph/0104255. doi:10.1126/science.292.5525.2211a. PMID 11423620. S2CID 14080941.

Observational

• Provencal, J. L.; Shipman, H. L.; Hog, Erik; Thejll, P. (1998). "Testing the White Dwarf Mass-Radius Relation with Hipparcos". The Astrophysical Journal. 494 (2): 759–767. Bibcode:1998ApJ...494..759P. doi:10.1086/305238.
• Gates, Evalyn; Gyuk, Geza; Harris, Hugh C.; Subbarao, Mark; Anderson, Scott; Kleinman, S. J.; Liebert, James; Brewington, Howard; et al. (2004). "Discovery of New Ultracool White Dwarfs in the Sloan Digital Sky Survey". The Astrophysical Journal. 612 (2): L129. arXiv:astro-ph/0405566. Bibcode:2004ApJ...612L.129G. doi:10.1086/424568. S2CID 7570539.
• McCook, G.P.; Sion, E.M., eds. (9 September 2013). "White Dwarf Catalogue WD". Villanova University. Archived from the original on 6 July 2024.
• Dufour, P.; Liebert, James; Fontaine, G.; Behara, N. (2007). "White dwarf stars with carbon atmospheres". Nature. 450 (7169): 522–4. arXiv:0711.3227. Bibcode:2007Natur.450..522D. doi:10.1038/nature06318. PMID 18033290. S2CID 4398697.

Johnjbarton (talk) 23:20, 27 November 2024 (UTC)Reply

My opinion is that articles should not have "Further reading" sections. If it can't be used as an inline citation, it shouldn't be in the article, and these can be removed. Z1720 (talk) 01:22, 28 November 2024 (UTC)Reply

I have nothing against "Further reading" sections in principle. On scientific topics, I can easily imagine reasonable use cases. For example, the text itself should be based on secondary sources (textbooks, review articles, etc.), but having ready access to the original, foundational publications is also helpful. So, it could happen that the footnotes are to secondary sources, and we supplement them with a short list of primary sources in another section. It's really no different than the Albert Einstein article having a § Publications list; ditto for J. Robert Oppenheimer (a GA and an FA respectively). We shouldn't be using those as inline citations, for the most part, but we should be listing them. It can also be the case that a source is too influential and noteworthy to omit completely, but it's also not suitable for the article as written — maybe it's written at too high a level of mathematical sophistication. That's quintessential "further reading", i.e., reading that carries the subject further than the article does. MTW or Jackson or Peres could each play this role, for example, depending on the subject.

As for this specific "Further reading" list, eh, I could take it or leave it. I don't think it's harmful. It's too short to be an egregious linkfarm. It doesn't exactly strike me as a list of historical classics, either, though. XOR'easter (talk) 03:32, 28 November 2024 (UTC)Reply