Transcript Accretion disk structure - Mullard Space Science Laboratory

Accretion disk structure
The accretion disk (AD) around a star can be
considered as rings or annuli of blackbody emission.
R* is the star’s radius.
.
R
Dissipation rate, D(R)
0.5

3GMM
M   R*  

 
1  
3
8R   R  
= blackbody flux
 T ( R)
4
Disk temperature
Thus temperature as a function of radius T(R):
.
 3GMM 
 R* 
1   
T ( R)  
3
 8R    R* 
We define the boundary
condition T* at radius R* :
Then when
R  R*
=>
0.5
1/ 4



 

.
 
 3GMM
M
1/ 4

T*  
3
 8R*  
T  T* R / R* 
3 / 4
Disk Luminosity
The total energy available from the accretion of
mass m onto M with radius R is:
Eacc = GMm
R
But not all of this has to be lost (ie radiated
from) the accretion disk – there may be other
processes involved…
Energy losses from the disk
R
Ebind ~ 0
Ebind = GMm
and Lbind = GMM
2R
2R
So the energy
and Ldisk = GMM
E
=
GMm
which has been
disk
2R
2R
lost in the disk by
= ½Lacc
m is: