Black Holes and Accretion: Observational Frontiers
Lead Research Organisation:
University of Cambridge
Department Name: Institute of Astronomy
Abstract
Black holes (BHs) are objects so dense that beyond a certain point even light cannot escape their gravitational attraction, and are prevalent throughout the universe. Supermassive black holes (SMBHs; weighing over a million suns) reside at the centre of every major galaxy, and large numbers of smaller stellar-remnant black holes (StMBHs; tens of solar masses), the evolutionary end-point for the most massive stars, are scattered throughout them.
There is much that we still do not understand about these enigmatic objects. Critically, we do not know how SMBHs grew to be so massive. We now know some SMBHs were already grown when the universe was still in its infancy (~1 billion years old), but we do not know how they were able to grow so quickly. We also see that BHs can launch extreme jets of material traveling close to the speed of light that can significantly influence their surroundings (feedback), but we do not understand how these jets are launched.
These are some of the most important issues in contemporary astrophysics research, and can be addressed by studying how matter falls onto the 'local' SMBHs/StMBHs in our own and neighbouring galaxies (accretion). Observations at X-ray wavelengths in particular have the power to probe the nature and geometry of the infalling material in the immediate vicinity of the black hole. With the recent launch of the NuSTAR observatory, and both the Astro-H and ASTROSAT observatories also soon to be launched, we are entering a period of unprecedented observational capabilities in the X-ray regime. My proposal aims to leverage these new facilities to improve our understanding of this complex accretion process, and in turn of SMBH growth and the physics of jet launching.
Astonishingly, black holes themselves are fully defined by two fundamental properties: mass and spin (rotation). BH spin is a quantity of key importance, as a variety of jet launching models predict that the energy associated with BH rotation may be harnessed to launch these extreme outflows. Measuring BH spin is therefore a vital step in testing these models, and is one of the primary goals of my research.
In terms of understanding SMBH growth, I will take a dual approach. First, spin measurements are again vital, as SMBH spin tells us about the history of how these objects grew: growth via random mergers (chaotic growth) should spin SMBHs down, while growth via periods of prolonged accretion (ordered growth) should spin them up. In addition to measuring spin for SMBHs in the local universe I will begin testing models for how SMBH growth should vary with cosmic time by extending these measurements to much more distant SMBHs with gravitationally lensed sources. These are rare cases in which a foreground galaxy is aligned with our line-of-sight to the SMBH, which acts as a natural lens and significantly magnifies the light received, allowing far more sensitive studies than would otherwise be possible!
Second, I will also study how accretion operates at the most extreme rates, necessary to rapidly grow the SMBHs observed in the early universe given the short growth time available. Accretion at these rates is poorly understood, so further observational constraints are vital. We now that a rare population of 'ultraluminous' X-ray sources are StMBHs exhibiting such accretion. These are therefore ideal targets for further study in order to understand this exotic regime.
In combination, this research will bring significant advances in our understanding of accretion, spin, jets and the formation of the most massive black holes.
There is much that we still do not understand about these enigmatic objects. Critically, we do not know how SMBHs grew to be so massive. We now know some SMBHs were already grown when the universe was still in its infancy (~1 billion years old), but we do not know how they were able to grow so quickly. We also see that BHs can launch extreme jets of material traveling close to the speed of light that can significantly influence their surroundings (feedback), but we do not understand how these jets are launched.
These are some of the most important issues in contemporary astrophysics research, and can be addressed by studying how matter falls onto the 'local' SMBHs/StMBHs in our own and neighbouring galaxies (accretion). Observations at X-ray wavelengths in particular have the power to probe the nature and geometry of the infalling material in the immediate vicinity of the black hole. With the recent launch of the NuSTAR observatory, and both the Astro-H and ASTROSAT observatories also soon to be launched, we are entering a period of unprecedented observational capabilities in the X-ray regime. My proposal aims to leverage these new facilities to improve our understanding of this complex accretion process, and in turn of SMBH growth and the physics of jet launching.
Astonishingly, black holes themselves are fully defined by two fundamental properties: mass and spin (rotation). BH spin is a quantity of key importance, as a variety of jet launching models predict that the energy associated with BH rotation may be harnessed to launch these extreme outflows. Measuring BH spin is therefore a vital step in testing these models, and is one of the primary goals of my research.
In terms of understanding SMBH growth, I will take a dual approach. First, spin measurements are again vital, as SMBH spin tells us about the history of how these objects grew: growth via random mergers (chaotic growth) should spin SMBHs down, while growth via periods of prolonged accretion (ordered growth) should spin them up. In addition to measuring spin for SMBHs in the local universe I will begin testing models for how SMBH growth should vary with cosmic time by extending these measurements to much more distant SMBHs with gravitationally lensed sources. These are rare cases in which a foreground galaxy is aligned with our line-of-sight to the SMBH, which acts as a natural lens and significantly magnifies the light received, allowing far more sensitive studies than would otherwise be possible!
Second, I will also study how accretion operates at the most extreme rates, necessary to rapidly grow the SMBHs observed in the early universe given the short growth time available. Accretion at these rates is poorly understood, so further observational constraints are vital. We now that a rare population of 'ultraluminous' X-ray sources are StMBHs exhibiting such accretion. These are therefore ideal targets for further study in order to understand this exotic regime.
In combination, this research will bring significant advances in our understanding of accretion, spin, jets and the formation of the most massive black holes.
Publications
Stern D
(2020)
A Redshift for the First Einstein Ring, MG 1131+0456
in The Astrophysical Journal Letters
Tomsick J
(2018)
Alternative Explanations for Extreme Supersolar Iron Abundances Inferred from the Energy Spectrum of Cygnus X-1
in The Astrophysical Journal
Tomsick John A.
(2018)
Alternative explanations for extreme supersolar iron abundances inferred from the energy spectrum of Cygnus X-1
in ArXiv e-prints
Tortosa A
(2016)
Broadband X-ray spectral analysis of the Seyfert 1 galaxy GRS 1734-292
in Monthly Notices of the Royal Astronomical Society
Tortosa A
(2018)
NuSTAR spectral analysis of two bright Seyfert 1 galaxies: MCG +8-11-11 and NGC 6814
in Monthly Notices of the Royal Astronomical Society
Vito F
(2018)
Heavy X-ray obscuration in the most luminous galaxies discovered by WISE
in Monthly Notices of the Royal Astronomical Society
Walton D
(2018)
Disentangling the complex broad-band X-ray spectrum of IRAS 13197-1627 with NuSTAR, XMM-Newton and Suzaku
in Monthly Notices of the Royal Astronomical Society
Walton D
(2018)
Super-Eddington accretion on to the neutron star NGC 7793 P13: Broad-band X-ray spectroscopy and ultraluminous X-ray sources
in Monthly Notices of the Royal Astronomical Society
Description | Careers Day Speaker at Collyers Sixth Form College |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Schools |
Results and Impact | I spoke about careers in research at the careers day for A-level students at Collyers Sixth Form College. The goal of the event is to showcase the varied career options that are available for students that choose to take STEM subjects at the undergraduate level, and to encourage them to consider choosing such subjects. Based on the questions afterwards, a number of the students seemed very interested in the possibility of going on to have research careers. |
Year(s) Of Engagement Activity | 2017 |
Description | Guest lectures to AY101 class at the University of Alabama |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Undergraduate students |
Results and Impact | Gave two guest lectures on black holes and neutron stars to the 2020/2021 AY101 classes (astronomy undergraduate students) at the University of Alabama. The talks sparked plenty of discussion with the student body afterwards, indicating a good level of interest in astronomy as a subject. |
Year(s) Of Engagement Activity | 2020,2021 |
Description | Guest speaker at the Institute of Astronomy public observing evenings |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | Every Wednesday evening throughout the Winter season he Institute of Astronomy hosts a public observing evening. Prior to going out to observe, the attendees receive a guest talk from a member of the department, in which I have participated. These are designed to help educate the public about astronomy in general, and recent areas in which astronomy research has progressed. These evenings are rather popular, even when the weather is poor! |
Year(s) Of Engagement Activity | 2018 |
URL | http://www.ast.cam.ac.uk/public/public_observing |
Description | Guest speaker for the Cambridge University Astronomical Society |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Undergraduate students |
Results and Impact | The Cambridge University Astronomical Society, a student-run organisation, run a weekly seminar series throughout term-time with guest lectures from professional astronomers, in which I have participated. These are primarily designed to help discuss recent areas in which astronomy research has progressed with other members of the university (although the events are also open to the public). These evenings are reasonably well attended, and the students are very enthusiastic. |
Year(s) Of Engagement Activity | 2017 |
URL | http://astronomy.soc.srcf.net/ |
Description | Institute of Astronomy Open Day |
Form Of Engagement Activity | Participation in an open day or visit at my research institution |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | The Institute of Astronomy Open Day is designed to help educate the general public (of all ages) about astronomy. As part of this event, we ran booth focused on black holes and high-energy astrophysics. This is an annual event, which is always very well attended (>500 attendees) and also very well received. |
Year(s) Of Engagement Activity | 2017 |
URL | http://www.ast.cam.ac.uk/public/open.day |