Black hole accretion and outflows: novel multi-wavelength perspectives
Lead Research Organisation:
Durham University
Department Name: Physics
Abstract
Black holes are unique natural laboratories. Recreating the high temperatures and stresses of infalling matter is impossible on Earth. This makes black holes ideal sites to study extreme cosmic environments. Yet astronomers have struggled to accurately measure even basic properties such as the sum total of energy output from black hole environments, or to understand the nature of powerful 'jets' of outflowing matter known to emerge from them.
This has not been for lack of trying. Massive black holes found in the nuclei of all large galaxies are often cocooned within obscuring layers of interstellar gas and dust which hide them from direct view. Additionally, bright young star clusters invariably clutter our view of black holes, making it impossible to isolate their emission.
Stellar-mass black holes pose separate challenges. These are the most compact astronomical objects known (with characteristic sizes of only ~30 km for a typical Galactic source). As matter accretes (infalls) on them, part of its energy emerges as strongly variable light and fast-outflowing matter, a manifestation of the chaotic environment from which it emerges. Analysis of the variability patterns can yield direct information on the physics of accretion and jets. But this requires the use of fast and sensitive cameras which have not been available until recently.
My work has opened up new avenues to explore these issues. By using the exquisite resolution provided by very large telescopes in Chile, I have shown that the infrared emission from dusty clouds in the immediate vicinities of massive black holes can be successfully isolated from surrounding stars. Furthermore, the infrared provides a perfect 'bolometric' (total) emission measure, giving us a new tool to probe these obscured black holes.
Secondly, in order to understand jet physics on short times, I have studied variable X-ray, infrared and visible light in Galactic black holes. Using a novel fast camera, I led a team to observe visible light fluctuations only a fraction (~1/20th) of a second long from stellar black holes. We were stunned to find remarkable patterns amidst the fluctuating noise in the form of optical flashes which are correlated with X-ray variations. The optical emission was widely thought to be a secondary response to primary X-ray outbursts, but the optical fluctuations that I discovered are much too speedy to fit this scenario. Instead, my findings point to fast and chaotic magnetic energy extraction in the outflowing jets of matter. Using NASA's latest infrared space telescope called WISE, I was next able to measure the magnetic field strength and physical dimensions of the inner jet, quantities which has long eluded direct measurement. Although radio telescopes have long studied emission from extended jets, using the optical and infrared instead allowed me to probe the physical conditions in the jet near its base. This is the first step for understanding the extreme physics of relativistic plasma acceleration in compact sources in detail.
So we now have two new direct handles to study accretion and outflows in black holes. But studies to date have only explored small and patchy collections of objects, so I am proposing to explore large and well-defined samples in the sky. I will carry out the first high resolution infrared survey of all X-ray bright massive black holes in the nearby Universe. And, I will systematically explore the jets in outbursting stellar-mass black holes in optical, infrared and X-rays.
Black holes span an incredible range of masses and sizes unlike any other cosmic source. The only way to gain full insight into their properties is to utilise all tools at hand. This is why I am proposing a multi-pronged and multi-wavelength approach. The advent of large infrared telescopes, as well as new cameras capable of fast imagery, makes this research very timely.
This has not been for lack of trying. Massive black holes found in the nuclei of all large galaxies are often cocooned within obscuring layers of interstellar gas and dust which hide them from direct view. Additionally, bright young star clusters invariably clutter our view of black holes, making it impossible to isolate their emission.
Stellar-mass black holes pose separate challenges. These are the most compact astronomical objects known (with characteristic sizes of only ~30 km for a typical Galactic source). As matter accretes (infalls) on them, part of its energy emerges as strongly variable light and fast-outflowing matter, a manifestation of the chaotic environment from which it emerges. Analysis of the variability patterns can yield direct information on the physics of accretion and jets. But this requires the use of fast and sensitive cameras which have not been available until recently.
My work has opened up new avenues to explore these issues. By using the exquisite resolution provided by very large telescopes in Chile, I have shown that the infrared emission from dusty clouds in the immediate vicinities of massive black holes can be successfully isolated from surrounding stars. Furthermore, the infrared provides a perfect 'bolometric' (total) emission measure, giving us a new tool to probe these obscured black holes.
Secondly, in order to understand jet physics on short times, I have studied variable X-ray, infrared and visible light in Galactic black holes. Using a novel fast camera, I led a team to observe visible light fluctuations only a fraction (~1/20th) of a second long from stellar black holes. We were stunned to find remarkable patterns amidst the fluctuating noise in the form of optical flashes which are correlated with X-ray variations. The optical emission was widely thought to be a secondary response to primary X-ray outbursts, but the optical fluctuations that I discovered are much too speedy to fit this scenario. Instead, my findings point to fast and chaotic magnetic energy extraction in the outflowing jets of matter. Using NASA's latest infrared space telescope called WISE, I was next able to measure the magnetic field strength and physical dimensions of the inner jet, quantities which has long eluded direct measurement. Although radio telescopes have long studied emission from extended jets, using the optical and infrared instead allowed me to probe the physical conditions in the jet near its base. This is the first step for understanding the extreme physics of relativistic plasma acceleration in compact sources in detail.
So we now have two new direct handles to study accretion and outflows in black holes. But studies to date have only explored small and patchy collections of objects, so I am proposing to explore large and well-defined samples in the sky. I will carry out the first high resolution infrared survey of all X-ray bright massive black holes in the nearby Universe. And, I will systematically explore the jets in outbursting stellar-mass black holes in optical, infrared and X-rays.
Black holes span an incredible range of masses and sizes unlike any other cosmic source. The only way to gain full insight into their properties is to utilise all tools at hand. This is why I am proposing a multi-pronged and multi-wavelength approach. The advent of large infrared telescopes, as well as new cameras capable of fast imagery, makes this research very timely.
People |
ORCID iD |
Poshak Gandhi (Principal Investigator / Fellow) |
Description | Better understanding of the way that some of the most extreme cosmic objects are powered. There are details associated with the continuance award ST/J003697/2. Please google "Poshak Gandhi" for my research results. |
Exploitation Route | Finding are being applied by other astronomers to develop novel models and carry out further observations of accreting sources. |
Sectors | Education,Energy,Other |
URL | http://www.southampton.ac.uk/~pg3e14/ |
Description | Findings are being heavily used by other astronomers for further research. |
First Year Of Impact | 2014 |
Sector | Education,Other |
Description | NAOJ visiting professorship |
Amount | ¥300,000 (JPY) |
Organisation | National Astronomical Observatory of Japan |
Sector | Academic/University |
Country | Japan |
Start | 06/2013 |
End | 07/2013 |
Description | UKIERI-UGC Thematic Partnership 2014-15 |
Amount | £32,000 (GBP) |
Funding ID | UGC-2014/15/02 |
Organisation | British Council |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 02/2015 |
End | 08/2016 |
Title | Mid-infrared Atlas |
Description | Largest atlas of high angular resolution observations of active galactic nuclei in the mid-infrared |
Type Of Material | Database/Collection of data |
Year Produced | 2014 |
Provided To Others? | Yes |
Impact | Many citations already within the first months of release. Expect a lot more over the coming years. |
URL | http://dc.zah.uni-heidelberg.de/sasmirala |
Description | NuSTAR team membership |
Organisation | California Institute of Technology |
Department | Caltech Astronomy |
Country | United States |
Sector | Academic/University |
PI Contribution | Science themes for investigation. |
Collaborator Contribution | Access to telescope observing time and technological expertise. |
Impact | A strong publication record. See publication list. |
Start Year | 2014 |
Description | Expert panel discussion for next Japanese X-ray space telescope |
Form Of Engagement Activity | A formal working group, expert panel or dialogue |
Part Of Official Scheme? | No |
Type Of Presentation | Keynote/Invited Speaker |
Geographic Reach | International |
Primary Audience | Participants in your research and patient groups |
Results and Impact | Astro-H HXI/SGD Science Workshop, Hiroshima Japan, 2014 Feb 24-25 New collaborations. |
Year(s) Of Engagement Activity | 2014 |
URL | http://www-heaf.hepl.hiroshima-u.ac.jp/hxisgdws14/index.html |
Description | Press release |
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 | Press release on new interesting result None that I am immediately aware of. |
Year(s) Of Engagement Activity | 2013 |
URL | http://www.eso.org/public/unitedkingdom/news/eso1327/ |
Description | Workshop local organiser : AGN vs. Star-formation |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | Conference of experts on the fate of gas in galaxies. Significant collaborative efforts between participants resulted. |
Year(s) Of Engagement Activity | 2014 |
URL | http://astro.dur.ac.uk/AGNvsSF/home.html |
Description | York Festival of India talk on astronomy |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | 35 public audience of all age groups students expressed wish to become astronomers |
Year(s) Of Engagement Activity | 2013 |
URL | http://eventful.com/events/york-festival-india-dr-poshnak-gandhi-lecture-/E0-001-060005124-5 |