The first quasars were identified as being extremely powerful objects at vast cosmological distances in 1963, by Maarten Schmidt, because of their strong radio emission. Yet now we know that only a few percent of quasars (also known as QSOs - the names are abbreviations of "quasi-stellar radio source" and "quasi-stellar object") emit so strongly at radio wavelengths. We also know that, among those that are strong radio emitters, there exists a variety of different shapes and sizes of the radio emitting region - in extreme cases we can see radio emission over a region of many Mpc (1Mpc = 1 million parsec = 3.26 million light years).

I have been working on the long standing problem of why some quasars are "radio-loud" - we now know that radio-loud quasars live only in the most massive host galaxies and that they are probably powered only by the most massive black holes, perhaps a billion times the mass of our Sun. Strangely, it seems as though the radio-loud quasars actually form a distinct population from the quasars that are "radio-quiet" - we need to understand this and from that gain a better understanding of how quasars work.

Relevant personal publications

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