Also, in the accretion disks dominated by magnetic pressure what is the order of this magnetic pressure in cgs units? Also what is the order of the magentic field in Gauss?
And finally are the magnetic fields in any way important in the collapsar model as well?
Answer by Indrani Banerjee, IISC Bangalore. I am just posting her comments from her e-mail.
There is no fixed magnitude of gas or radiation pressure for a particular disk. Both the pressues vary with distance from the black hole.
The gas pressure in collapsar accretion disks is given by P_gas = rho k_B
T/m_N, and the radiation pressure P_rad =(1/3) a T^4, where rho is the
density, k_B is Boltzmann's constant, T is temperature, m_N is mass of
nucleon, and a is radiation density constant. You have to know the
temperature and the density profile in order to estimate their magnitude.
You can find the temperature and density profile of collapsar I accretion
disk in Chen & Beloborodov 2007 (ApJ 657, 383) and collapsar II accretion
disk in our RAA paper.
As far as 'The Standard Disk' (Shakura-Sunyaev disk) is concerned the
outer and the middle region of the disk is dominated by gas pressure, i.e,
the total pressure is almost equal to the gas pressure while the inner
disk is radiation pressure dominated. The expressions for gas and
radiation pressure are same as above. The temperature and density profiles
for Shakura-Sunyaev/Novikov-Thorne disk is given in Abramowicz & Fragile
2013 (Living Review in Relativity, 16,1). So, once you know the
temperature and density profiles you can easily estimate the magnitudes of
the gas and radiation pressures.
Moving on to your last question, magnetic fields are important in
collapsar accretion disks as they often help in driving jets and outflows
from the disk.
- Badges
- Science topic