/Liverpool’s Sky At Night … Tricia Sullivan

/Community News

Date: 13th December 2018

Liverpool’s Sky At Night … Tricia Sullivan

In the first of a weekly services, we will hear from the people who conduct their research at iC2 and are setting the pace globally. Their research interests are as varied as they are, and so we are delighted to introduced the human faces behind the science, starting with Tricia Sullivan.

Tricia Sullivan is an American-born Irish citizen in the UK. She began studying physics with the Open University as a forty-something mum of small children, moved on to LJMU’s distance learning MSc, and is now a member of LIV.DAT, the Centre for Doctoral Training in data science here in Liverpool. She is also a science fiction novelist—but that’s on pause because a PhD is more than enough work. Her website is triciasullivan.com and she is @InGutterLooking on Twitter.

Black holes are paradoxical beasts. They can’t been seen directly because they are so massive that they curve spacetime and warp the path of light into a singularity; that’s why every photon that gets close to a black hole disappears forever beyond its event horizon. Yet despite being invisible by definition, supermassive black holes in the centres of galaxies are also responsible for some of the most luminous objects in the Universe. This apparent paradox is possible because of the way supermassive black holes devour the inner regions of the galaxies they inhabit. In gas-rich galaxies, as material falls into the galactic centre (or nucleus) it forms a disk that orbits rapidly around the black hole. Close to the centre, this disk gets so hot and turbulent that it shines at high energies and can produce magnetic field lines that extend to great distances. The field lines often regulate powerful outflows of hot, luminous gas belched out by the black hole as it feeds.

Optical telescopes find thousands of these ‘active galactic nuclei’ (AGN); they can outshine their own galaxies and may look as bright as stars in our sky, although they are often billions of light years away. But unlike most stars, AGN don’t shine steadily. They flicker erratically. The relationship between variability amplitude, wavelength, and timing in AGN can tell us about the physical characteristics of the black hole and its accretion disk. But there are many challenges in assembling this information; for one thing, up to ten years of well-sampled data may be needed to fully capture the variability. The Large Synoptic Survey Telescope (LSST) is due to survey the entire southern sky every few days, generating about 20 terabytes of data every night. Over time, LSST will enable us to study many more AGN than ever before; however, the sheer volume of data requires us to develop new methods of analysis.

My PhD with Professor Iain A. Steele at the Astrophysics Research Institute is about developing software to process AGN signals in batches and so establish relationships between variability and known physical characteristics. Eventually I’ll be testing some machine learning techniques to do this, but at the moment I’m generating simulated data to find out how typical sampling patterns of telescopes affect the statistical properties of the models that astrophysicists use. Unlike most variable stars that change in predictable ways, AGN luminosity changes stochastically; i.e., its fluctuations are essentially unpredictable. However, if telescopes go offline for maintenance at the same time every year for several years, this sampling pattern can imprint itself on the signal and create a false impression of structure in the model. It’s important for me to get to grips with these effects before analysing survey data, or the conclusions I draw could well be wrong. Luckily, AGN behaviour is stable over many thousands of years, so the signals will still be there when I eventually get round to looking at some real data.

The Astrophysics Research Institute (ARI) is part of Liverpool John Moores University and based in the IC2 building at the Liverpool Science Park. Comprised of nearly seventy research staff and forty graduate students, the work of the ARI encompasses a range of observational and theoretical research: Star Formation and Stellar Populations, Time Domain Astrophysics (focussing on rapidly changing astrophysical phenomena such as supernovae), Galaxy Formation and Evolution, Astronomical Instrumentation, and Computational Cosmology.
Additionally, the ARI works with the University of Liverpool to deliver Bachelor and Master’s courses in astronomy, and also provides a range of distance learning courses. Through its operation of the world’s largest robotic telescope, the National Schools’ Observatory provides data and telescope time to schools around the UK, helping to make professional astronomy accessible to the next generation