# White dwarf accretion

1. Sep 22, 2008

### Sanjay87

Hi,

Let's say we have a white dwarf accreting material from a giant partner. How long would it typically take for the white dwarf to go supernova? Is it of the order of a thousand years? A million? Any references would be much appreciated.

Thanks,
San

2. Sep 23, 2008

### entorm

Townsley and Bildsten (2003) (http://xxx.lanl.gov/abs/astro-ph/0309208) find accretion rates for cataclysmic variables 10^(-11) - 10^(-8) Msun/yr, but I am sure you can find more papers on this (I just did a very short search), and different values depending on the assumptions.

A very rough estimate: the Chandrasekhar limit of 1.38 solar masses could be reached in approximately 3.8 10^7 - 3.8 10^10 years, assuming that you start with a white dwarf of 1 solar mass and accrete at the above rate.

There is a lot of work going on on this subject and the mechanism of type Ia supernovae is still not well understood. I think you would find the existing literature very interesting.

3. Sep 23, 2008

### stevebd1

Out of general interest, do you have any idea what the accretion rate is for a neutron star in a binary system?

4. Sep 23, 2008

### entorm

I don't have a number to give you on neutron stars, but here is a simple way to calculate an accretion rate:
A rough theoretical estimate for the accretion rate on a disk is given by the luminosity of the disk:

L{disk} = G M M{dot} / 2R

where L{disk} the disk luminosity, M{dot} the mass accretion rate and M and R the mass and radius of the accreting object (you find a derivation in 'An Introduction to Modern Astrophysics' by Carroll and Ostlie).

The maximum luminosity an object can have and still stay in hydrostatic equilibrium is given by the Eddington limit:

L{max} / L_sun = 3.8 10^4 (M/M_sun)

Substituting the Eddington limit in the first equation can give you an estimate of the highest possible accretion rate.

I hope this helped! People more relevant to the field could post answers based on current research.