Jodrell Bank Centre for Astrophysics

Our Research

Research

Cartoon showing AGN model

The title of my thesis is "Multiwavelength Studies of Radio-Loud Active Galactic Nuclei in the Fermi Era". This basically means that I am taking observations across the entire electromagnetic spectrum of galaxies with very bright centres to try to understand the physics that drives them. The "in the Fermi era" part is because my project was partially motivated by the launch of the Fermi Gamma-ray Space Telescope in 2008.

Active Galactic Nuclei (AGN) are galaxies that appear to be emitting far more energy from their centres than can be explained by their stars. There are many types of extragalactic object that can be classified as AGN including quasars, Seyfert galaxies, blazars and radio galaxies. The problem is that while each group of object will have some properties in common with another group, there is not one single set of observational properties that describe all AGN.

Theories proposed to explain the different properties seen in AGN are called 'unified models'. The most widely accepted of these says that there is a central supermassive black hole surrounded by an accretion disk with clouds of gas further out, radio jets emitting from the poles, and a ring or torus of dust enclosing the inner structure. The cartoon to the right illustrates this model. The radio jets are responsible for the extended radio structure seen in a lot of AGN, the clouds of gas emit the broad and narrow optical emission lines seen in most AGN, the material in the accretion disk emits in the UV and X-ray as it spirals into the black hole. By changing the angle at which we look at this system, we can explain, for example, why some AGN don't have broad emission lines (obscured by the dusty torus) or why we only see one sided radio structure in other AGN (one jet directed away from us).

The AGN that I am interested in are those where one of the radio jets is directed towards us. These objects are known as 'blazars'. Because the jet is pointed towards us and travelling at relativistic speeds, the emission is Doppler boosted. This means that blazars appear to be some of the most extreme objects in the Universe (and have even been dubbed "Nature's Death-Ray Gun" in one article!).