Re: Bolometric Magnitude of non-Main Sequence Stars

Crown-Horned Snorkack wrote:

On 28 sept, 03:24, Erik Max Francis <m...@xxxxxxxxxxx> wrote:

Lang gives the absolute visual (not bolometric) magnitude of white
dwarfs as 12.13 +- 1.54 magnitudes.

Um, far too narrow.

Well, you can look up your own figure then. That was for a prototypical white dwarf.

Unlike a main sequence star, which fuses protium at a sustained steady
rate for a long time, both white dwarfs and neutron stars are devoid
of internal energy source. They cool by radiating away their heat
capacity.

The age for which white dwarfs and neutron stars have cooled ranges
from 12-13 milliards of years to far below this.

White dwarfs haven't been around for this long. The first generation of stars were all supermassive stars that went supernovae; they left no white dwarfs.

White dwarfs only became possible when the interstellar medium was enriched enough to create second-generation stars. The Sun is somewhere between a second- and third-generation star. So the average age of a white dwarf you see today is not nearly as old as you seem to think.

So... do we have a clue as to how fast white dwarfs and neutron stars
cool?

Very slowly. They can only lose heat by radiation, and they have very small surface areas, so the blackbody power law says that they are very inefficient at releasing their heat. (Same goes for neutron stars, but with even more of a vengeance.) The timescale is on the order of a few billions of years (Shapiro, Tuekolsky).

--
Erik Max Francis && max@xxxxxxxxxxx && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM, Y!M erikmaxfrancis
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-- Lamya
.

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