occasional meanderings in physics' brave new world

Name:
Location: New Zealand

Marni D. Sheppeard

## Saturday, October 24, 2009

### White Dwarfs

A Kiwi astronomer has been telling me about his work on white dwarf stars, which are the end states of around 99% of all stars. In theory, white dwarfs cool quickly due to neutrino emission from the core in a photon decay process

$\gamma \mapsto \nu + \overline{\nu}$

from photons that acquire an effective mass due to the plasma medium. This mass depends on the core density of the star. One aims to measure cooling rates for such stars by observing changes in the periods of their pulsation.

A Mt John result focuses on the fairly stable pulsating hot dwarf star EC20058-5234, which is about $0.55$ the mass of the sun. This is the only known stable white dwarf of DBV type. For such a hot star, plasmon neutrino cooling should be far more important than photon emission from surface processes. However, constraints on plasmon neutrino emission for this star, in terms of period decay, currently lie around $10^{-13} s s^{-1}$.

Some authors have also considered novel cooling processes for white dwarfs, such as axion emission.

CarlBrannen said...

These are interesting reactions because they are essentially impossible to detect in earthbound detectors due to their rarity.

My intuition says that if there's something here, it will have to do with very parallel decay products. Wish I had time to think about it more.

P.S. Never rely on astrophysicists to draw your Feynman diagrams; they're confused with their neutrino arrows. Ah, what can you expect for people who think that oxygen is a metal?

October 27, 2009 4:40 PM
CarlBrannen said...

You should read this fascinating article on the weirdness in quasi stellar objects (QSOs).

October 27, 2009 8:37 PM