Accretion Disc - Science topic

Draw.io is a good choice for the diagrams, but may be too general.

Also, I use GeoGebra for illustrating ideas in a geometrical sense.

The Boltzmann interpretation of temperature is that it is related to particle velocity. Considering that many of the particles in an accretion disk are expected to be electrically charged the magnetic field would be expected to cause a geometrically anisotropic distribution of temperature and associated thermal effects. This obviously complicates analysis of the thermal profile.

https://science.sciencemag.org/content/358/6368/1299

Their study shows that B is around for 33 G for V404 Cygni

Snigdha Das I will send you a direct message

It's against the mainstream, but there is a reason why the strength of gravity might decrease for masses with mass/radius ratio approaching c^2/G. If incoming matter approaching the centre of a galaxy reaches this limit the gravity reduces and the pressure forces an ejection perpendicular to the disc.

http://vixra.org/abs/1802.0167 Appendix B3. After the ejection the mass/radius ratio is reduced and so the ejections only happen periodically, that's why only a few galaxies appear to have AGNs.

A lot.

mostly non-thermal mechanisms should be considered.

The Rayleigh criterion, relies on fluid elements retaining their angular momenta.

Following Rayleigh, suppose we interchange the fluid in two rings, of equal masses, at radii r1 and r2 . So the fluid initially at r1 is moved to r2 , conserving its angular momentum L1 . Similarly the fluid initially at r2 is moved to r1 , conserving its angular momentum L2 . Then,

change in KE ∼ (L2^2 − L1^2 )(r1^-2 - r2^-2)

Now a system always wants to go to the lowest energy state. If angular momentum is a increasing function of r, then the swapping of fluid parcels is going to cost the system to increase its energy, so the system will not try to do it and the system is stable to this perturbation.

However in case when angular momentum is a decreasing function of r, then the system can release its energy by swapping of fluid parcels and the system will try to do so, so the system is unstable to this perturbation.

So we can say that when the angular momentum is a increasing function of r in an accretion disk, the disk is Rayleigh stable.

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.

Dear Martin,

I like very much your gedanken speculations, which demonstrate high level of your knowledge and creative power. Thank you.

Unfortunately, in this specific case the question is in, perhaps, different conditions in disc and halo for Li7 origin, due to different type of stars (and, therefore, different abundances of elements), different fluxes of ancient and contemporary cosmic rays, etc.

In old white dwarfs of halo Li7 is considered to be cosmological one. In which processes has its abundance grown in order of magnitude, observed in contemporary stars of disc, if Li7 is disturbed in thermonuclear reactions?

In the middle of the last century W. Fowler suggest a hypothesis on LiBeB origin in spallation reactions. I succeeded in arguing it, considering spallation reactions with shock wave accelerated particles (there are many references of my works in RG). I would like concretize this process in various galactic circumstances. I need to know, at least, the difference in types of stars in disc and halo.