Seeing to the Event Horizons of Supermassive Black Holes

Astronomy Colloquium, The Pennsylvania State University (22/09/2021)

Physics Colloquium, Stanford University (28/09/2021)

Colloquium, South African Astronomical Observatory (30/09/2021)

Physics Colloquium, Julius-Maximilians Universität, Würzburg (18/10/2021)

Physics Colloquium, Wayne State University, Detroit, MI (24/02/2022)

Supermassive black holes in the centers of galaxies power some of the brightest objects we see in the Universe; active galactic nuclei (AGN). Much remains unknown, however, about exactly how energy is released from the material falling in through the accretion disk, and from the black hole itself, to power these extreme systems, form a luminous X-ray emitting corona, and launch jets at almost the speed of light.

The X-rays emitted from the corona illuminate the material falling into the black hole and by measuring its reflection, we obtain a unique insight into the processes occurring just outside the event horizon. Most recently, measuring the echoes of X-ray flares emitted by the corona, we have been able to obtain the most detailed map of the structure of the inner accretion disk and corona, and have been able to detect the reverberation of the X-ray flare from material that should classically be hidden behind the shadow of the black hole.

The reverberation of X-ray flares is letting us see the corona evolve in real time and witness the effects of strong gravity and general relativity as the X-rays are bent around the black hole. This gives us important insight into the small-scale processes close to the event horizon that allow black holes to power these extreme objects and play their important feedback role in the formation of structure in the Universe.

Seeing to the Event Horizons of Supermassive Black Holes

• SLAC Colloquium, SLAC National Accelerator Laboratory (10/05/2021)

• Astrophysics Colloquium, Stanford University – 26/06/2020

Supermassive black holes in the centers of galaxies power some of the brightest objects we see in the Universe; active galactic nuclei (AGN). Much remains unknown, however, about exactly how energy is released from the material falling in through the accretion disk, and from the black hole itself, to power these extreme systems, forming a powerful X-ray emitting corona and launching jets at almost the speed of light.

The X-rays emitted from the corona illuminate the material falling into the black hole and by measuring its reflection, we obtain a unique insight into the processes occurring just outside the event horizon. Most recently, measuring echoes of X-ray flares emitted by the corona, and comparing these measurements to the predictions of general relativistic ray tracing simulations, we have been able to obtain the most detailed map of the structure of the inner accretion disk and corona.

The reverberation of X-ray flares is letting us see the corona evolve in real time and witness the effects of strong gravity and general relativity as the X-rays are bent around the black hole. This gives us important insight into the small-scale processes close to the event horizon that allow black holes to power these extreme objects and play their important feedback role in the formation of structure in the Universe.

Mapping the Extreme Environments Around Black Holes

Spitzer Seminars, California State University, East Bay, Hayward, CA (11/10/2018)
Institute of Astronomy Seminars, University of Cambridge (20/06/2018)

Some of the brightest and most extreme objects we see in the Universe are, powered by matter spiralling into a supermassive black hole in the centre of a galaxy. As matter falls into the black hole, intense radiation is released, outshining the stars in these galaxies and many of these black holes are able to launch jets of particles close to the speed of light that span vast distances out of the galaxy. Many of the physical processes by which vast amounts of energy is released and injected into the surroundings remain a mystery.

Detailed observations of supermassive black holes in Seyfert galaxies with the large X-ray observatories XMM-Newton, Suzaku and NuSTAR, have revealed an unprecedented amount. I will discuss, in particular, how the effects of general relativity imprinted upon X-rays that are reflected from the inner regions of the disc of infalling material provide a unique probe of the extreme environment around the black hole. This lets us map out the innermost regions, just outside the event horizon of the black hole and gives us important insight into the processes by which these extreme systems are powered. We are starting to learn how these processes are governed over long timescales as supermassive black holes played their vital role in the formation of structure we see in the Universe today.

Seeing to the Event Horizons of Supermassive Black Holes

INPA Seminars, Lawrence Berkeley National Laboratory, Berkeley, CA (23/02/2018)
Physics Colloquia, University of Notre Dame, South Bend, IN (22/03/2017)

Active galactic nuclei (AGN) are some of the most luminous objects in the Universe, powered by the accretion of matter onto a supermassive black hole in the centre of a galaxy, yet many of the physical processes by which vast amounts of energy is released and injected into the surroundings remain a mystery.

Detailed observations of supermassive black holes in Seyfert galaxies with the large X-ray observatories XMM-Newton, Suzaku and NuSTAR, have revealed an unprecedented amount. I will discuss, in particular, how the effects of general relativity imprinted upon X-rays that reverberate from the inner regions of the disc of accreting material provide a unique probe of the extreme environment around the black hole. 

The reflected X-rays reveal the structure of the powerful X-ray emitting corona and its evolution as the luminosity we observe varies by more than an order of magnitude. This gives us important insight into the processes by which these extreme systems are powered and by which some black holes are able to launch jets of particles at close to the speed of light. We are starting to learn how these processes are governed over cosmic time as supermassive black holes played their vital role in the formation of structure we see in the Universe today.

Revealing the Dynamic X-ray Sources and Jet Launching from Black Holes

CASA/JILA Astrophysics Seminars, University of Colorado, Boulder, CO (06/03/2015)

Active galactic nuclei (AGN) are some of the most luminous objects we see in the Universe, powered by the accretion of matter onto a supermassive black hole in the centre of a galaxy, yet many of the physical processes by which vast amounts of energy is released and injected into the surroundings remain a mystery.

X-rays are emitted from a 'corona' of energetic particles surrounding the black hole and as well as being observed directly, they are seen to be reflected from the accreting disc, producing a number of spectral features including emission lines that are broadened by relativistic effects in the proximity of the black hole. I will discuss how detailed measurement of the reflected X-rays from the accretion disc using the large X-ray observatories, XMM-Newton and Suzaku, can be used to probe the innermost regions of accretion flow and corona, right down to the innermost stable orbit and the event horizon.

Novel spectral analysis techniques allow us to reconstruct, from the observed relativistic X-ray reflection spectrum, the spatially resolved illumination pattern of the accretion disc and I will discuss how comparing this to the results of systematic general relativistic ray tracing simulations, we are able to constrain the location and geometry of the X-ray emitting corona and understand the dramatic changes this corona undergoes, driving extreme variability in the emitted X-rays and potentially driving jets.

I discuss how measurements of the X-ray variability, specifically the reverberation time lags that are observed between variability in the directly observed X-rays from the corona and those reflected from the accretion disc add a further dimension to the study of accreting black holes, letting us not only build up a three dimensional image of the immediate vicinity of the black hole but also to probe mechanisms by which the energy is released from the accretion flow; techniques that will let us exploit not just current instrumentation but future proposed X-ray observatories to really put theories of black holes and accretion to the test and understand such extreme objects and how they shape Universe.

Seeing to the Black Hole Event Horizon in AGN with X-ray Observations

Astrophysics Seminars, University of Notre Dame, South Bend, IN (17/02/2015)
Physics Seminars, St. Francis Xavier University, Antigonish, NS (23/01/2015)
Physics Seminars, Mount Allison University, Sackville, NB (18/09/2014)

Active galactic nuclei (AGN) are some of the most luminous objects we see in the Universe, powered by the accretion of matter onto a supermassive black hole in the centre of a galaxy. Many of the physical processes by which vast amounts of energy are released and injected into the surroundings, however, remain a mystery.

X-rays are emitted from a 'corona' of energetic particles surrounding the black hole and as well as being observed directly, they are seen to be reflected from the disc of material spiralling into the black hole. The reflected X-rays are bent and shifted in energy by the strong gravitational field in the proximity of the black hole.

I will discuss how detailed measurement of the reflected X-rays using the large X-ray observatories, XMM-Newton and Suzaku, can be used to probe the innermost regions of accretion flow and corona, right down to the innermost stable orbit and the event horizon.

By connecting these observations to theoretical predictions and computer simulations, we are able to build up a three dimensional image of the extreme environment around the black hole and understand how such extreme objects are powered and how they shape Universe.

X-ray Reflection as a Probe of Accreting Black Holes

24/02/2014 — CITA National Fellows' Meeting, University of Toronto (24/02/2014)
14/02/2013 — Astrophysics Seminars, University of Bristol, UK (14/02/2013)
11/01/2013 — Astronomy & Physics Colloquia, St. Mary's University, Halifax, NS (11/01/2013)

Active galactic nuclei (AGN) are some of the most luminous objects we see in the Universe, powered by the accretion of matter onto a supermassive black hole in the centre of a galaxy, yet many of the physical processes by which the energy is released and injected into the surroundings remain a mystery.

X-rays are emitted from a 'corona' of energetic particles surrounding the black hole and as well as being observed directly, they are seen to be reflected from the accreting disc, producing a number of spectral features including emission lines that are broadened by relativistic effects in the proximity of the black hole. I will discuss how detailed measurement of the reflected X-rays from the accretion disc can be used to probe the innermost regions of accretion flow and corona, right down to the innermost stable orbit and the event horizon.

Novel spectral analysis techniques allow us to reconstruct, from the observed relativistic X-ray reflection spectrum, the spatially resolved illumination pattern of the accretion disc and I will discuss how comparing this to the results of systematic general relativistic ray tracing simulations I have developed, we are able to constrain the location and geometry of the X-ray emitting corona and understand the dramatic change of the narrow line Seyfert 1 galaxy 1H 0707-495 into an extremely low flux state in terms of a collapse in the corona as well as the changes AGN undergo all the time, driving their extreme variability in the emitted X-rays.

I will discuss how measurements of the X-ray variability, specifically the reverberation time lags that are observed between variability in the directly observed X-rays from the corona and those reflected from the accretion disc add a further dimension to the study of accreting black holes, letting us not only build up a three dimensional image of the immediate vicinity of the black hole but also to probe mechanisms by which the energy is released from the accretion flow; techniques that will let us exploit not just current instrumentation but future proposed X-ray observatories to really put theories of black holes and accretion to the test and understand such extreme objects and how they shape Universe.