Supermassive black hole growth - a small-scale solution to a large-scale problem

Lead Research Organisation: University of Southampton
Department Name: School of Physics and Astronomy

Abstract

In the centre of almost every galaxy sits a dark object, with a mass over a million times that of the Sun. Although massive, these objects have been compressed by their own gravity to extremely high densities, so dense in-fact that light cannot escape their surface; these are the supermassive black holes (SMBHs). How these exotic objects formed is one of the outstanding mysteries facing astronomers and one I find particularly intriguing.

By looking to great distances we are able to glimpse what happened in the first few billion years of the Universe's life. Although very difficult to perform studies at these distances, a few SMBHs can be 'weighed'. Surprisingly this has shown that they were fully-grown when the Universe was only ~1 billion years old. Although scientists thought that growth should take a long time, this discovery demands that they instead grew incredibly quickly by material falling onto the black hole at extreme rates - faster than should be allowed by the balance of radiation and gravity, the so-called Eddington limit. How accretion operates at such rates is unclear but is a pressing issue in astrophysics - an issue I aim to address.

Although we cannot study the SMBHs growing directly, we can observe how material falls onto SMBHs in nearby galaxies and onto much smaller black holes (with orbiting stars in binary systems: BHBs) within our own Galaxy. As a result, we know that material doesn't fall directly onto the black hole but forms an accretion disc, which emits large amounts of radiation. At very high rates, not all of the material falls onto the black hole; instead some fraction is expelled in 'winds' or 'jets'. Winds carry material from the surface of the disc at fairly 'slow' speeds (~10% of the speed of light) whereas jets are much more powerful ejections of matter from close to the black hole at almost the speed of light. It is logical that similar outflows will have accompanied the SMBH growth, with matter taken from the accretion flow and redistributed to the surroundings - a form of 'feedback'.

Understanding the nature of Eddington accretion and the associated outflows is necessary for understanding the growth of SMBHs and the impact feedback must have had on the host galaxy. In practice this requires observing how the accretion flow changes as it reaches the Eddington limit and couples to the outflow, i.e. how they interact. In practice this has proven to be extremely difficult: emission from the accretion flow onto both SMBHs in nearby galaxies and onto Galactic BHBs is obscured by intervening material, preventing a view of the coupling. My proposal approaches this problem in a new way: by looking at BHBs accreting at high rates in nearby galaxies where the amount of intervening material is much lower, allowing the emission from the inflow to be studied. These extragalactic BHBs come in two 'flavours': those which are commonly seen in the Milky Way and show powerful jets, and those which are even brighter and thought to be a more extreme form of Eddington accretion with powerful winds.

I am leading the first major search for new BHBs with powerful jets in two nearby galaxies. By observing with several instruments across a range of wavelengths, including the world's foremost radio telescope, the VLA, and NASA's X-ray satellite, Swift, I will observe how the disc and jets change together, thereby constraining both the nature of the inflow and how the jets are launched. In order to understand the brightest sources with powerful winds, I will combine novel analysis techniques with theory to reveal the nature of both inflow and outflow. By studying accretion onto SMBHs in the local Universe, I will extrapolate my findings to larger black hole masses where the coupling of inflow and outflow cannot be studied. Finally, by using simulations of high redshift SMBH growth I will be able to explore the impact of feedback on the host galaxies, in an epoch otherwise hidden from view.

Publications

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Alston W (2019) The remarkable X-ray variability of IRAS 13224-3809 - I. The variability process in Monthly Notices of the Royal Astronomical Society

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Alston W (2019) The remarkable X-ray variability of IRAS 13224-3809 - I. The variability process in Monthly Notices of the Royal Astronomical Society

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Anderson G (2019) Discovery of a radio transient in M81 in Monthly Notices of the Royal Astronomical Society

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Ashton D (2021) Searching for energy-resolved quasi-periodic oscillations in AGN in Monthly Notices of the Royal Astronomical Society

Related Projects

Project Reference Relationship Related To Start End Award Value
ST/M005283/1 01/10/2015 30/09/2016 £392,086
ST/M005283/2 Transfer ST/M005283/1 03/10/2016 31/12/2021 £314,834
 
Description RAS Council
Geographic Reach National 
Policy Influence Type Membership of a guideline committee
 
Description Binary population synthesis 
Organisation University of Warsaw
Country Poland 
Sector Academic/University 
PI Contribution A key component of the ERF project is the connection of ULX physics to the high redshift Universe. My collaboration with Dr Chris Belzynski and Dr Grzegorz Wiktorowicz is bearing fruit and the completed simulations are expected to place limits in the ionizing flux by ULXs as a function of redshift - potentially important to the nature of local environments and contribution to re-ionisation (should their number be significant)
Collaborator Contribution Dr Chris Belzynski and Dr Grzegorz Wiktorowicz have written and executed the code, I am using the meta products.
Impact The first paper has now been accepted and several further papers are in preparation.
Start Year 2016
 
Description EC status renewal 
Organisation Max Planck Society
Department Max Planck Institute for Astronomy
Country Germany 
Sector Academic/University 
PI Contribution I am an external collaborator in the eROSITA mission, renewed for 2020. I am leading a number of key ULX projects. Renewal is now being applied for
Collaborator Contribution N/A
Impact No outputs yet
Start Year 2018
 
Description Modelling of ULX nebulae 
Organisation University of Amsterdam
Country Netherlands 
Sector Academic/University 
PI Contribution I have entered into a new collaboration with Prof Sera Markoff and Dr Tobias Beuchart at the University of Amsterdam where we will be taking the 3D kinetic and radiative energy output from simulations (see previous mention of my award of HPC time) to compare to observations of nebulae surrounding ULXs to determine whether additional physical components are required. A paper is in prep and will soon be submitted.
Collaborator Contribution Prof Sera Markoff and Dr Tobias Beuchart are using bespoke codes to determine the energy deposition by winds (which take as input the simulations I am coordinating with Dr Jan-Fei Jiang, Prof Shane Davis and Prof Jim Stone).
Impact The first paper from this collaboration is now in preparation.
Start Year 2017
 
Description NuSTAR 
Organisation California Institute of Technology
Department Caltech Astronomy
Country United States 
Sector Academic/University 
PI Contribution I am an ongoing member of the ULX and binaries NuSTAR working groups. Whilst the core science period has ended, the collaboration is highly successful and remains productive (see the many papers based on NuSTAR data). Notably a new paper (of which I am co-author) from the ULX collaboration is about to be published in Nature Astronomy with an associated press release. I continue to lead multiple NuSTAR projects connected to the ERF project and these are close to journal submission.
Collaborator Contribution My partners are the members of the NuSTAR science teams.
Impact I am co-author on several papers as a consequence of my NuSTAR team membership (see portfolio) with the results from the large campaign on SS433 (for which I was PI) now submitted.
Start Year 2015
 
Description SMARTNet 
Organisation University of Geneva
Country Switzerland 
Sector Academic/University 
PI Contribution In 2015 I chaired an international meeting of directors and key scientists at the Lorentz Centre, NL. The result of this meeting is a review/white paper of which I am first author (New Astronomy Reviews) which has now been published. Our associated network entitled "SMARTNet" has now gone live (http://www.isdc.unige.ch/SmartNet/) and is being used to coordinate observations of new transients at multiple wavelengths.
Collaborator Contribution My partners are the members of SMARTNet.
Impact The community white paper has now been published
Start Year 2016
 
Description STROBE-X 
Organisation Texas Tech University
Country United States 
Sector Academic/University 
PI Contribution I am a collaboration member for the new proposed NASA (probe class) satellite mission, STROBE-X and am performing investigative work to establish its potential to study ULXs and better probe the physics of such accretion flows.
Collaborator Contribution The proposed mission is being led by one of my collaborators, Prof Tom Macaroni
Impact The mission planning is in its early stages but a white paper should be published in the next year
Start Year 2017
 
Description Theoretical modelling of ULXs 
Organisation College of Charleston
Country United States 
Sector Academic/University 
PI Contribution I continue to explore the theoretical aspects underpinning the ERF project and by virtue of an award of DiRAC time I have cemented my collaboration with Drs Yan-Fei, Shane Davis and Jim Stone. We are in the process of applying for additional HPC time with which we will explore the parameter space for the large scale-height accretion flow in ULXs (and AGN at super-Eddington accretion rates), needed to create models for comparison to current and next-generation data.
Collaborator Contribution My partners are world-leading, US based theorists who have developed advanced numerical codes for describing accretion flows.
Impact We have one paper submitted and more to follow. We await the outcome of the latest DiRAC round after which we hope to perform further simulations.
Start Year 2016
 
Description Theoretical modelling of ULXs 
Organisation Kavli Institute For Theoretical Physics
Country United States 
Sector Academic/University 
PI Contribution I continue to explore the theoretical aspects underpinning the ERF project and by virtue of an award of DiRAC time I have cemented my collaboration with Drs Yan-Fei, Shane Davis and Jim Stone. We are in the process of applying for additional HPC time with which we will explore the parameter space for the large scale-height accretion flow in ULXs (and AGN at super-Eddington accretion rates), needed to create models for comparison to current and next-generation data.
Collaborator Contribution My partners are world-leading, US based theorists who have developed advanced numerical codes for describing accretion flows.
Impact We have one paper submitted and more to follow. We await the outcome of the latest DiRAC round after which we hope to perform further simulations.
Start Year 2016
 
Description Theoretical modelling of ULXs 
Organisation University of Virginia (UVa)
Country United States 
Sector Academic/University 
PI Contribution I continue to explore the theoretical aspects underpinning the ERF project and by virtue of an award of DiRAC time I have cemented my collaboration with Drs Yan-Fei, Shane Davis and Jim Stone. We are in the process of applying for additional HPC time with which we will explore the parameter space for the large scale-height accretion flow in ULXs (and AGN at super-Eddington accretion rates), needed to create models for comparison to current and next-generation data.
Collaborator Contribution My partners are world-leading, US based theorists who have developed advanced numerical codes for describing accretion flows.
Impact We have one paper submitted and more to follow. We await the outcome of the latest DiRAC round after which we hope to perform further simulations.
Start Year 2016
 
Description ULX radio monitoring 
Organisation University of Oxford
Department Department of Physics
Country United Kingdom 
Sector Academic/University 
PI Contribution I am leading the coordination of several radio campaigns to study ULXs. Observations are being made by AMI-LA, VLA and eMERLIN, and we have submitted a proposal to use MeerKAT with a view to submitting a request for an SKA program. A new campaign is starting in March coordinated between XMM-Newton and VLA of which I am the PI.
Collaborator Contribution I have written most of the proposals requesting time on the instruments.
Impact We are in the process of writing a high-impact paper that also utilises data from NASA's NICER mission.
Start Year 2018
 
Description eROSITA 
Organisation Max Planck Society
Department Max Planck Institute For Extraterrestrial Physics (MPE)
Country Germany 
Sector Academic/University 
PI Contribution I remain an active external collaborator for the eROSITA satellite mission (due for launch in mid-2019) and - in collaboration with a colleague at the University of Durham (Prof Tim Roberts) - have been awarded performance verification (PV) time to study a bright ULX which shows pulsations. In addition I am now a member of an additional eROSITA project to study TDEs and transient ULXs. This directly connects to (and extends) the proposed science of my ERF project to study transient ULXs, and builds upon my existing and ongoing project to monitor M31 with NASA's Swift satellite in order to find new sources (supported by continued awards of time from NASA's Chandra and ESA's XMM-Newton satellites).
Collaborator Contribution My partners are the science team members of the eROSITA mission.
Impact There no outputs to report yet although there is a paper in preparation related to ULX demographics.
Start Year 2017
 
Description BBC World Service 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact I was interviewed for the BBC World Service (CrowdScience) on the dual particle-wave name of light. The typical reach of the program is enormous and intended for non-scientists in the developed and developing world. I am recording another segment in the near future.
Year(s) Of Engagement Activity 2018
 
Description BBC radio 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact In addition to public lectures (see portfolio), I have also appeared a number of times on the BBC Radio Cambridge show 'The Naked Scientists' for their live Q&A, fielding astronomy questions which have touched upon my research (specifically astrophysical jets) and have provided a pre-recorded segment on the physics of black holes.
Year(s) Of Engagement Activity 2016
 
Description Press release (Nature Astronomy) 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact I am leading the University of Southampton press release for a paper (on which I am co-author) being published in Nature Astronomy. The paper details the discovery of a cyclotron resonant scattering feature which provides an estimate for the magnetic field strength of the neutron star in a ULX for the first time. I am also being interviewed live on US radio (Sciencefriday)
Year(s) Of Engagement Activity 2018
URL https://www.sciencefriday.com
 
Description Press release to accompany Nature Astronomy publication 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact A press release was carried out by the University of Southampton to coincide with the publication of a Nature Astronomy paper (on which I was co-author).
Year(s) Of Engagement Activity 2018
 
Description The Naked Scientists 2017 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact I have continued to appear on the BBC Radio Cambridge show 'The Naked Scientists' for their live Q&A, fielding astronomy questions which have touched upon my research.
Year(s) Of Engagement Activity 2017