Talk:White dwarf

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.

Neon-22 distillation

Here's another topic that probably should be covered by this article:

• Blouin, Simon; Daligault, Jérôme; Saumon, Didier (April 2021). "²²Ne Phase Separation as a Solution to the Ultramassive White Dwarf Cooling Anomaly". The Astrophysical Journal Letters. 911 (1). id. L5. arXiv:2103.12892. Bibcode:2021ApJ...911L...5B. doi:10.3847/2041-8213/abf14b.{{cite journal}}: CS1 maint: unflagged free DOI (link)

There are a number of papers available on Neon-22 Distillation, so the topic appears notable. Praemonitus (talk) 00:36, 4 February 2025 (UTC)

Okay, I found the section where the white dwarf cooling anomaly is discussed. Never mind... Praemonitus (talk) 14:27, 5 February 2025 (UTC)

This is an awesome piece, — Preceding unsigned comment added by JohannaLeblanc (talk • contribs) 00:27, 24 June 2025 (UTC)

Sea of Blue

The lead is a sea of blue. Could we tidy this up a bit? Links to common terms like helium don't need to be in the lead. They can be linked later on. Tayste (edits) 20:23, 24 June 2025 (UTC)

Plural White dwarf star

The plural form of "white dwarf star" is "white dwarf stars" sometimes abbreviated as "white dwarfs" but not "white dwarves". See for examples

• Weidemann, V. (1968). White dwarfs. Annual Review of Astronomy and Astrophysics, vol. 6, p. 351, 6, 351.
• Isern, J., Garcia-Berro, E., Torres, S., & Catalan, S. (2008). Axions and the cooling of white dwarf stars. The Astrophysical Journal, 682(2), L109.
• D'Antona, F., & Mazzitelli, I. (1990). Cooling of white dwarfs. IN: Annual review of astronomy and astrophysics. Vol. 28 (A91-28201 10-90). Palo Alto, CA, Annual Reviews, Inc., 1990, p. 139-181., 28, 139-181.

Johnjbarton (talk) 16:12, 25 June 2025 (UTC)

Unverified content

@Praemonitus You reverted my edit. Did you read the source? Is says nothing about He burning. It's about evidence that low mass white dwarf stars are in binary systems. What is your basis for claiming my version does not make sense? Johnjbarton (talk) 03:09, 4 July 2025 (UTC)

You said that low mass main sequence stars are only in binary systems. Praemonitus (talk) 03:23, 4 July 2025 (UTC)

Ah, I see I was changing the existing text about "white dwarf stars" without noticing that that was not how the sentence started. Thanks for the fix up. Johnjbarton (talk) 21:24, 4 July 2025 (UTC)