Institute for Astronomy

Active Galactic Nuclei PhD Projects

Research projects on offer in our Active Galactic Nuclei group

Assembly of the most massive black holes in the universe

James Aird

Video: Aird
PhD Project 2022

Supermassive black holes, with millions to billions of times the mass of the Sun, are found at the centres of most galaxies and may play a fundamental role in shaping the structure and evolution of the galaxies they lie. In the nearby universe, we are able to track the motion of stars and gas in the very centres of some galaxies, allowing us to measure the masses of their black holes. The most massive black holes, with up to 10 billion solar masses, are found at the centres of massive, red elliptical galaxies in the nearby universe. This PhD project will focus on understanding how and when these extreme black holes assembled their mass. Prior studies have tended to focus on the assembly of more typical supermassive black holes, finding that these black holes grow through periods of accretion when they are seen as Active Galactic Nuclei (AGN) and that this mechanism proceeds in tandem with the growth of the bulk of galaxies through star formation. We will instead focus on these more extreme monsters to understand when and how they grew over cosmic time. We will start by considering their host galaxies, diagnosing how these galaxies have evolved and identifying their progenitors in the more distant universe. We will then use deep X-ray survey data to assess when such galaxies hosted luminous AGN and track the growth of their black holes back in time. The student will also have the exciting opportunity to engage in the new `black hole mapper' programme - part of the fifth generation of the international Sloan Digital Sky Survey (SDSS-V) project - which is providing optical spectroscopic follow-up of X-ray AGN that have been found across the sky with the recently launched eROSITA X-ray telescope. We will use the incoming SDSS-V data to directly identify the most massive black holes over cosmic time as they grow, constrain their incidence, extract the properties of their host galaxies, and thus determine how such objects can produce the massive black holes in the nearby universe.

Extreme variability in AGN

Andy Lawrence

Video: Extreme variables in AGN
Extreme variables in AGN

All Active Galactic Nuclei (AGN) are erratically variable to some extent. Light curves can give us information on size scales no other technique can reach. Recently however we have come to realise that a significant minority of AGN undergo dramatic changes - either long slow outbursts over many years, or appearing out of nowhere over days and then fading over months. Possible explanations include accretion instabilities, tidal disruption of stars, and microlensing caused by an intervening object. A new generation of telescopes - especially PanSTARRS, ZTF and soon LSST - are systematically scanning the sky trying to spot such outbursts, and projects such as PESSTO are aimed at getting their spectra  as rapidly as possible. Three projects are possible in this area:

  • Spectra: Joining the PESSTO consortium, collecting and analysing spectra of rapid transients - suspected total disruption events and “changing look” quasars.
  • Data Mining: Collating a database of tens of thousands of AGN, their properties, and their light curves; looking for correlations, and critically testing theoretical predictions.
  • Machine Learning and Forecasting (CDT project): Developing novel algorithms to test whether we can forecast which AGN are about to undergo outburst; using this to get critical pre-outburst spectra.