Warming White Dwarfs with Dark Matter

Two recent arXiv preprints discuss capture of Dark Matter and limits on its self-annihilation inside white dwarfs…

Capture of Inelastic Dark Matter in White Dwarves

Inelastic Dark Matter As An Efficient Fuel For Compact Stars

…the first discusses limits for inelastic Dark Matter capture inside the white dwarfs of globular cluster M4, while the second discusses capture in general. PhysicsWorld.com has a commentary news-piece on the limits and the putative inelastic DM signal from the DAMA/LIBRA experiment… Warm white dwarfs could reveal ‘inelastic’ dark matter …and mentions white dwarfs maintaining an even 7000 K temperature, rather than cooling towards ~3000 K (what the coolest WDs radiate at.)

What does that mean, in the long term, I wondered? Consider the average white dwarf, which is about 0.7 solar masses and about 0.0093 solar radii. Call it 0.01 size of the Sun. At 7000 K each square metre is radiating x2.15 times the Sun’s 5780 K, thus the white dwarf is putting out about 0.0002 Solar luminosities – i.e. about 5000 white dwarfs would equal the Sun. Since the galaxy is expected to evolve to a state of being either white dwarfs or brown, then there will be about ~20 million solar luminosities worth of Dark Matter annihilation energy radiating from them until the Dark Matter runs out some time between 10¹⁹ – 10²⁰ years from now.

The SETI implications are interesting – does it imply that civilizations with an extremely long-view will ultimately move into residence around white dwarfs? Such would live ~1-10 million times longer than red-dwarf based societies, which is quite impressive. Of course a mere 10²⁰ years is nothing compared to eternity…