Professors David Roberts and John Wardle are involved in observational astronomy and cosmology at wavelengths covering the entire electromagnetic spectrum, but especially at radio wavelengths. They are particularly interested in cores of “active galaxies”— Seyfert galaxies, powerful radio galaxies, quasars and BL Lacertae objects.
Making use of the radio telescopes of the National Radio Astronomy Observatory and the international Very Long Baseline Interferometry (VLBI) Network, they are studying the angular structure and polarization of extragalactic radio sources in detail at resolutions ranging from arcminutes down to milliarcseconds.
Recent 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 is about to yield an entirely new value for the Hubble constant, which determines the scale and age of the universe. 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.
The Brandeis astrophysics group has pioneered the technique of making linear polarization maps at milliarcsecond resolution using VLBI. These experiments are revealing for the first time the magnetic field structure in compact radio sources (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.