Mariko T. Kato, Masaki Fujimoto, Shigeru Ida
We have studied formation of planetesimals at a radial pressure bump in a
protoplanetary disk created by radially inhomogeneous magnetorotational
instability (MRI), through three-dimensional resistive MHD simulations
including dust particles. In our previous papers, we showed that the
inhomogeneous MRI developing in non-uniform structure of magnetic field or
magnetic resistivity can transform the local gas flow in the disk to a
quasi-steady state with local rigid rotation that is no more unstable against
the MRI. Since the outer part of the rigid rotation is super-Keplerian flow, a
quasi-static pressure bump is created and dust concentration is expected there.
In this paper, we perform simulations of the same systems, adding dust
particles that suffer gas drag and modulate gas flow via the back-reaction of
the gas drag (dust drag). We use O(10^7) super-particles, each of which
represents many dust particles with sizes of centimeter to meter. We have found
that the dust drag suppresses turbulent motion to decrease the velocity
dispersion of the dust particles while it broadens the dust concentrated
regions to limit peaky dust concentration, compared with the simulation without
the dust drag. We found that reduction in the velocity dispersion) is dominated
over the suppression in particle concentration. For meter-size particles with
the friction time ~1/Omega, where Omega is Keplerian frequency, the
gravitational instability of the dust particles that may lead to planetesimal
formation is expected. For such a situation, we further introduced the
self-gravity of dust particles to the simulation to demonstrate that several
gravitationally bound clumps are actually formed. Through analytical arguments,
we found that the planetesimal formation from meter-sized dust particles can be
possible at ~5AU, if dust spatial density is a few times larger than that in
the minimum mass solar nebula.
View original:
http://arxiv.org/abs/1112.5264
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