[Physics-grads-open] PASS talk on Stellar Accretion Disks

[Pooyan Goodarzi]

Hi all,


We will have a PASS talk by Morgan on *Monday, March 2nd*. Please join
us at noon (*from 12:00 to 1:00 pm*) in the *Conference Room* (PHYS 3051).


*Morgan Ohana, PhD Student*
 Monday, 12:00 pm, Conference Room (PHYS 3051)

*Simulations of Eccentricity Growth in Compact Binary Accretion Disks with
Magnetohydrodynamic Turbulence*
We present the results of four magnetohydrodynamic simulations and one
alpha-disk simulation of accretion disks in a compact binary system,
neglecting vertical stratification and assuming a locally isothermal
equation of state. We demonstrate that in the presence of a net vertical
field, disks that extend out to the 3:1 mean-motion resonance grow
eccentricity in full MHD in much the same way as in hydrodynamical disks.
Hence, turbulence due to the magnetorotational instability (MRI) does not
impede the tidally driven growth of eccentricity in any meaningful way.
However, we find two important differences with alpha-disk theory. First,
in MHD, eccentricity builds up in the inner disk with a series of episodes
of radial disk-breaking into two misaligned eccentric disks, separated by a
region of circular orbits. Standing eccentric waves are often present in
the inner eccentric disk. Second, the successful spreading of an accretion
disk with MRI turbulence out to the resonant radius is nontrivial—and much
harder than spreading an alpha disk. This is due to the tendency to develop
overdense rings in which tidal torques overwhelm MRI transport and truncate
the disk too early. We believe that the inability to spread the disk
sufficiently was the reason why our previous attempt to excite eccentricity
via the 3:1 mean-motion resonance with MHD failed. Exactly how MHD disks
successfully spread outward in compact binary systems is an important
problem that has not yet been understood.



*If you’re interested in sharing your work as a speaker, please feel free
to add your name to this spreadsheet [Google Sheet
<https://docs.google.com/spreadsheets/d/1N3ncf43jdB6aHYHhyWmyHMycxDg4_phHZXLkQvviO0o/edit?usp=sharing>].
Recordings of all the previous talks are available on our website:
https://ucrpass.arxiv.social <https://ucrpass.arxiv.social/>*


Best,
Pooyan
Physics and Astronomy Student Seminar (PASS)
https://ucrpass.arxiv.social
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