Astronomy & Physics
UC Berkeley Astronomy Department
601 Campbell Hall
Berkeley, CA 94720-3411
Compact Objects, Instabilities, MHD, Plasma Physics, Relativistic Outflows.
I am a professor of theoretical astrophysics and plasma physics in the Astronomy Department and the Physics Department at UC Berkeley. I am also a member of the Theoretical Astrophysics Center. Aside from my professional life as a teacher and researcher in Astrophysics and Plasma Physics, I enjoy cooking and playing the ‘cello.
I was born in Philadelphia, Pennsylvania on August 16, 1943, and lived there for 18 years; I received my B.A. in Physics from Williams College in 1965 and my Ph. D. in Astronomy from Harvard University in 1970. I was a postdoctoral Fellow at the Princeton University Observatory and the Institute for Advanced Study for 2 years before coming to Berkeley in 1972.
I am fascinated by the physics of compact astrophysical objects, especially neutron stars. I am intrigued by the bizarre behavior of fully ionized plasmas, which mix long range electromagnetic forces with kinetic particle behavior. I merge these interests by studying the magnetospheres of neutron stars and their interactions with their environs, and their role in the acceleration of the highest energy cosmic rays. I also have interests in the magnetized accretion disks around black holes, whose physics has similarities to that of the outflows from rotation powered pulsars.
Time Dependent Structure of Relativistic Shocks:
Theory and simulation of relativistic collisionless shock wave structure, with application to the termination shocks of the pulsars’ winds in the Crab Nebula and in other pulsar driven nebulae, and in jets emerging from the disks around black holes, including Gamma Ray Bursts. Recent and current projects include a) a hybrid (MHD electrons and positrons, kinetic high energy ions) theory of the shock structure terminating the wind in the Crab Nebula – a Chandra image of the Crab showing the inner X-ray ring whose time dependent properites are similar to the hybrid model, is shown on the left, the wave strudture in the hybrid model is in the middle; an image of the magnetic structure of a shoick wave of the kind found in Gamma Ray Bursts appears on the right. b) A calculation of the nonthermal particle spectrum generated in these shock structures of this type. c) Coherent radiation emitted by these shocks.
|Crab Nebula in X-Rays||Hybrid Theory of Spherical Shock Structure –
Magnetically Reflected Ions with Resulting Compressions and Brightness Enhancements
|Magnetic Structure of a Collisionless Shock,
from a large Particle-in-Cell simulation
Structure and Instability of Current Sheets, with application to Relativstic Outflows and to Accretion Disks
Pulsars’ winds and jets from black holes contain wound up magnetic fields. Fields of opposite polarity are separated by intense sheets of electric current. Such current sheets are subject to dissipative processes, which result in the conversion of magnetic eneregy in heat (including particles with nonthermal energy spectra) and large scale plasma motion. Both effects are central to an outstanding puzzle raised by observations of relativstic outflows, the disappearance of magnetic energy and its reappearance as outflowing kinetic energy in. I am studying a novel mechanism through which this conversion can occur, through the conversion of the energy contained in the current sheets into intense, quasi-coherent electromagnetic radiation, whose absorption gives rise to the plasma acceleration. I am also engaged in studying current sheets in turbulent magnetic flow, with application to plasma heating and particle acceleration in accretion disks around black holes.
My astrophysical publications can be found on the web astro-ph website or at the Astrophysics Data System (ADS) website.
My plasma physics publications can be found in pdf format here
My curriculum vitae and complete publications are available in pdf format here.