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Our group has pioneered the techniques of making linear polarization images at milliarcsecond resolution using VLBI. Recently, we have extended our techniques to measure the circularly polarized signals that originate from compact radio sources. These experiments are revealing for the first time the magnetic field structure in these compact objects (where apparent motions in excess of the speed of light are often observed), and the nature of the plasma surrounding the massive black hole thought to exist at the center of these sources.
Early programs using the
Very Large
Array (VLA) in New Mexico include a
detailed radio study of the famous gravitationally-lensed double quasar
0957+561. Continuing monitoring of this quasar provides a measurement of
the Hubble constant that is completely independent of traditional
techniques (
Roberts,Lehar, Hewitt, & Burke, Nature, 352, 43
(1991)). The VLA has also been used to make extremely high quality
maps of the radio "jets" in many quasars, in order to understand the
mechanism by which enormous amounts of energy are transported from the
cores to the outer radio lobes.
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The Brandeis Radio Astronomy Group conducts research in extragalactic
astrophysics and cosmology at wavelengths covering the entire
electromagnetic spectrum, but especially at radio wavelengths. We are
particularly interested in cores of "active galaxies" or "blazars" -
powerful radio galaxies, quasars, BL Lacertae objects, and Seyfert
galaxies. Making use of the