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Astrophysics Luncheon Seminar

The Migrating Embryo Model of Protostellar Disk Evolution and Planet Formation
Presented by Shantanu Basu
Department of Physics and Astronomy, Western University, Ontario, Canada

Monday, November 2, 2015
12:00 noon in 169-336

Abstract
I present numerical simulations that follow the collapse of a cloud core down to the formation of a protostellar disk. A burst mode of accretion begins upon the formation of a centrifugally balanced disk around a newly formed protostar. It is comprised of prolonged quiescent periods of low accretion rate (typically less than about 10^{-7} solar mass per year) which are punctuated by intense bursts of accretion (typically greater than about 10^{-4} solar mass per year, with duration less than about 100 years) during which most of the protostellar mass is accumulated. The accretion bursts are associated with the formation of dense protostellar/protoplanetary embryos, which are generally driven onto the protostar by the gravitational torques that develop in the disk. We conclude that most (if not all) protostars undergo a burst mode of evolution during their early accretion history, as inferred empirically from observations of FU Orionis variables. Migrating embryos can also sometimes create a gap in the disk and settle into stable orbit as a companion to the central star. In other cases they can be ejected from the system as protostars, proto-brown dwarfs, or protoplanets. During the quiescent phase between the bursts and in the late accretion phase when the bursts have subsided, the sustained action of gravitational torques due to nonaxisymmetric perturbations drives a low-level accretion that agrees with observed values in T Tauri disks and enforces a surface density distribution proportional to r^{-3/2}.

JPL Contact: Walid Majid (4-6621)


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