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NASA award enables astrophysicist to study mysterious quasars

Ohad Shemmer, Assistant Professor of Physics; photo by Jonathan ReynoldsOhad Shemmer, right, assistant professor of physics, has earned a National Aeronautics and Space Administration (NASA) General Observer award to continue his study of a group of mysterious quasars in the distant universe. Shemmer’s observations have been made using the European X-­ray satellite, XMM-­Newton.

“The entire community of astronomers wants half a day or even an hour with that satellite – it’s very competitive,” Shemmer said. “So if you can get two of these observations, you are very lucky.”   

Shemmer is an astronomer who uses multi-­wavelength observations to assess the properties of black holes found in the nucleus of nearly every galaxy - supermassive black holes that can range in mass from a million to more than a billion solar masses. By observing the full spectrum of light emissions such as the ultraviolet, optical, infrared, and X-­ray bands, he is able to determine the properties of these supermassive black holes, especially in active galactic nuclei (AGN), where they are actively growing by gas accretion.  

Since 2005, Shemmer has turned his attention to a group of quasars – or extremely powerful AGNs – that emit curiously weak emission lines. Quasars are some of the most powerful astrophysical sources, and distant quasars that show high redshifts in their spectra can reveal information about the environment in the early universe. Why these particular quasars display contradictory characteristics is a question of debate among observers and well worth his attention.

His project, “Weak Line Quasars at High Redshift: Extremely High Accretion Rate Sources?,” will focus on the accretion rates of these quasars as one possible explanation to solve the mystery behind their extremely weak emission lines.  

The XMM images will augment Shemmer’s prior observations from ground-­based telescopes in Hawaii and Chile. “The idea is to gather data from the optical, infrared, and from the X-­rays on these mysterious quasars and combine the knowledge to learn something new about the quasar population as a whole,” Shemmer said.

— Amelia Jaycen, publications intern, Office of Research and Economic Development


Posted on: Tue 12 February 2013

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