Christian Knigge

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Professor Christian Knigge
Astronomy Group
Physics & Astronomy
University of Southampton
Southampton SO17 1BJ
United Kingdom
tel: +44-(0)2380-593-955

My Research

I have quite a broad range of research interests, including accretion onto compact objects, binary evolution, stellar exotica in globular clusters, type Ia supernovae and their progenitors, (astro-)statistics, and the physics of accretion and outflows in quasars.

You can get a complete list of my publications from either the ADS or the arXiv.

If you are interested in doing a PhD with me, check out the list of projects here and/or feel free to contact me.

Recent Highlights

  • Accretion onto Compact Objects: Most of my work in this area so far has centered on accreting white dwarfs, although I am also interested in neutron stars and black holes. In fact, I am particularly fascinated by the apparent universality of the accretion process. For example, we have recently discovered that accreting white dwarfs produce radio jets, just like neutron stars and black holes; that they exhibit the same hysteretic behaviour during their dwarf nova eruptions as do black holes and neutron stars during their X-ray outbursts; and that they even display the same non-linear stochastic variability -- the so-called rms-flux relation -- as neutron stars and black holes.

  • Binary Evolution: The formation and evolution of compact binary stars remains very poorly understood. This  matters, because it prevents us from obtaining a reliable census of many astrophysically important objects (such as type Ia supernovae, novae, ultracompact binaries that may be detectable gravitatational wave sources, etc, etc). My recent efforts here have included the construction of a comprehensive semi-empirical donor sequence for accreting white dwarf binaries and, building on this, the reconstruction of the secular evolution path of these compact binaries. Retha Pretorius and I have also recently measured the space density and X-ray luminosity function of accreting white dwarfs, which are two of the most fundamental observables that can be used to test theoretical models.

  • Stellar Exotica in Globular Clusters: Globular clusters are old, gravitationally-bound stellar systems that  contain up to a million stars. Their cores are extremely dense, so that collisions and near misses between clusters members can be quite frequent. These interactions can produce a wide range of interesting and exotic objects, which can in turn control the evolution of their host clusters. Recent highlights include a spectroscopic survey of stellar exotica in the proto-typical cluster 47 Tucanae, the discovery/confirmation of ultra-compact X-ray binaries in M15 and NGC 1851, and the discovery of a correlation between blue straggler numbers and cluster core mass that hints at a binary origin for the mysterious blue straggler stars.

  • Accretion and Outflows in Active Galactic Nuclei and Quasars: The central engines of quasars and AGN are accreting supermassive black holes, and it is becoming increasingly clear that the universality of the accretion process extends even to these objects. For example, in a recent key study led by my Southampton colleague Ian McHardy, we established that we can really think of active galactic nuclei as scaled-up stellar mass black holes. I am also interested in the connection between accretion and outflows -- specifically disk winds -- in quasars. These outflows represent a critical form of feedback, by which the black hole can influence its galactic environment. The clearest observational tracer of these disk winds are broad absorption lines, so we have used the Sloan Digital Sky Survey to estimate the intrinsic incidence of these wind-formed features in quasars. We are now trying model these outflows in detail, in an effort to uncover their geometry and kinematics, as well as their mass and energy budget. Thanks to the similarity of the accretion process on all scales, we are able to do this by building on a code originally developed for modelling accreting white dwarfs (mainly by our collaborator Knox Long).
  • Galactic Plane Surveys: I am involved in several ongoing efforts to map the plane of our Galaxy -- the Milky Way -- with modern CCD detectors in a variety of wavelengths. The umbrella organization for these efforts is EGAPS (European Galactic Plane Surveys), which, in the northern hemisphere, includes IPHAS (an Hα survey) and UVEX (a UV-excess survey), and, in the southern hemisphere, VPHAS+ (a combined Hα and UV-excess survey). One key contribution Southampton has already made to these efforts is the construction of the IPHAS emission line source catalogue.

  • X-ray Pulsars and Supernovae: My Southampton colleague Malcolm Coe is responsible for getting me interested in X-ray pulsars and their connection to Type II supernovae. In particular, we discovered evidence for two distinct populations of X-ray pulsars in the neutron star spin period distribution of the so-called Be/X-ray binaries, the most common class of X-ray pulsars.

Interested in talking to me about research? Contact Me!

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