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2005 ASP Annual Award Recipients

Robert J. Trumpler Award
Siming Liu
Ph.D. granted by University of Arizona, Department of Physics (now at Stanford University, USA)

The Trumpler award is shared this year by two promising young astronomers, Jennifer Scott and Siming Liu. Siming Liu received his Ph.D. degree from the University of Arizona in September 2002. For his thesis work, Liu carried out theoretical modeling of accretion processes around the closest supermassive black hole candidate, Sgr A*. The study of accretion flow reveals properties of the spacetime geometry near the event horizon and, therefore, reveals properties of the black hole itself. Supermassive black holes are particularly good subjects for study because their large mass allows them to capture efficiently plasma from the interstellar medium. This plasma is then compressed and accelerated, producing strong radiation.

Liu’s models span a broad range of the electromagnetic spectrum and were employed to constrain the nature of radio emission in the spectrum of Sagittarius A* at the Galactic center. His research suggests that a sub-millimeter hump in the radio spectrum arises from hot magnitized gas orbiting within about ten Schwarzschild radii of the black hole. His models have also been applied to M31* in the center of the Andromeda galaxy; M31* is more than ten times as massive than Sgr A*. Interestingly, although the x-ray luminosity of M31* is thousands of times greater than that of Sgr A*, its radio luminosity is lower than Sgr A* by a factor of three. Liu’s multi-wavelength models for these two supermassive black holes show that Sgr A* is smaller and hotter with a low accretion rate, while M31* is big, cold, and accretes very rapidly.

Liu’s thesis work demonstrates an unusual level of creativity and scientific rigor. As a graduate student, he established himself as a prolific researcher, publishing five papers in the Astrophysical Journal in just over a year. Liu is currently a postdoctoral scholar at Stanford University.