Black hole accretion and outflows: novel multi-wavelength perspectives

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

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.

Publications

10 25 50

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Aharonian F (2017) Hitomi Constraints on the 3.5 keV Line in the Perseus Galaxy Cluster in The Astrophysical Journal

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Aharonian F (2017) Hitomi Constraints on the 3.5 keV Line in the Perseus Galaxy Cluster in The Astrophysical Journal

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Aharonian H (2018) Hitomi observations of the LMC SNR N 132 D: Highly redshifted X-ray emission from iron ejecta* in Publications of the Astronomical Society of Japan

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Aharonian H (2018) Search for thermal X-ray features from the Crab nebula with the Hitomi soft X-ray spectrometer* in Publications of the Astronomical Society of Japan

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Alfonso-Garzón J (2018) Optical/X-ray correlations during the V404 Cygni June 2015 outburst in Astronomy & Astrophysics

Related Projects

Project Reference Relationship Related To Start End Award Value
ST/J003697/1 25/03/2013 02/11/2014 £457,498
ST/J003697/2 Transfer ST/J003697/1 03/11/2014 02/04/2018 £309,066
 
Description Significant new knowledge generated:

1) X-ray and infrared observations of black holes that I have led or participated in have revealed unexpected results on black holes. I list 3 examples below:

i) the revision of the standard unification model of black holes:
https://www.eso.org/public/news/eso1327/;

ii) The discovery of clumpy structures around deeply hidden black holes:
http://www.jpl.nasa.gov/news/news.php?feature=4798;

iii) The discovery of puzzling correlations in black hole power based upon exhaustive studies:
http://adsabs.harvard.edu/abs/2015MNRAS.454..766A

iv) Discovery of red flashes from the base of a black hole jet, giving new insight into black hole energetics:
http://www.southampton.ac.uk/news/2016/03/red-flares-black-hole.page


Noteworthy invitations:

My research resulted in me being invited by Nature magazine as an external expert to provide commentary on black hole variability research:
http://adsabs.harvard.edu/abs/2016Natur.529...28G

Particularly significant workshops organised:

1) Large international workshop on AGN unification:
http://torus2015.sungrazer.org

2) Workshop with high level worldwide observatory directors on the theme of multiwavelength simultaneous astronomy:
https://lorentzcenter.nl/lc/web/2015/713/info.php3?wsid=713

Future pathways:

1) Science team member of the Hitomi mission, which is just beginning operations and will undoubtedly yield great science within the coming years:
http://www.southampton.ac.uk/news/2016/02/poshak-gandhi-astroh-space-telescope.page

2) Affiliate PI in LSST:UK collaboration.

3) External collaborator status in eROSITA consortium.

4) IAA Grant (£31.5k) awarded to build new fast optical cameras to probe rapid black hole flaring.

5) Starting AstroSat collaboration with IUCAA, India.
Exploitation Route Black holes tell us about extreme physical conditions in the universe, which surely influences our culture and education on a range of levels. Fast frame rate digital detector technologies have been boosted as a result of my work on black hole variability.
Finally, understanding how black holes can generate their huge energy reservoirs could potentially lead to breakthroughs in the energy sector.
Sectors Digital/Communication/Information Technologies (including Software),Education,Energy

URL https://www.nature.com/natastron/volumes/1/issues/12
 
Description The press releases that I have been involved with have an estimated audience reach of more than 100 million people. Artist illustrations showing simple research concepts that my research has created can be found all over the internet and so are influencing popular culture. My Nature articles have had a broad impact, leading to invitations to speak on the radio, and being quoted on news websites internationally. My group continues to grow with 3 students and at least one incoming postdoc. I have a permanent academic position in a reputable university.
Sector Education,Other
Impact Types Cultural,Societal

 
Description Strategising for the future of UK X-ray astronomy
Geographic Reach Europe 
Policy Influence Type Participation in a national consultation
URL https://sites.google.com/site/ukxrayastro/
 
Description Workgroup on Simultaneous Multiwavelength Astronomy
Geographic Reach Multiple continents/international 
Policy Influence Type Participation in a advisory committee
URL https://lorentzcenter.nl/lc/web/2015/713/info.php3?wsid=713
 
Description GCRF
Amount £111,000 (GBP)
Organisation Science and Technologies Facilities Council (STFC) 
Sector Public
Country United Kingdom
Start 04/2018 
End 04/2019
 
Description Impact Acceleration Account
Amount £31,500 (GBP)
Organisation Science and Technologies Facilities Council (STFC) 
Sector Public
Country United Kingdom
Start 07/2016 
End 12/2016
 
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
 
Description VC Studentship
Amount £20,000 (GBP)
Organisation University of Southampton 
Sector Academic/University
Country United Kingdom
Start 09/2017 
End 09/2018
 
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 AstroSat collaboration with IUCAA 
Organisation Inter-University Centre for Astronomy and Astrophysics (IUCAA)
Country India 
Sector Learned Society 
PI Contribution Joint PhD student training.
Collaborator Contribution We have signed an MoU and are sharing student training.
Impact UKIERI Thematic partnerships in 2014 were what led us to formalise our present agreement. More outcomes expected in 2017, with a new student expected to be recruited.
Start Year 2017
 
Description Hitomi science team membership 
Organisation Japanese Aerospace Exploration Agency
Country Japan 
Sector Public 
PI Contribution Preparation for first observations by the Hitomi satellite
Collaborator Contribution They are the mission leads so control all aspects of the project.
Impact Hitomi Collaboration Nature paper and 3.5 keV dark matter line search ApJ paper published. Preparations for re-flight mission well under way.
Start Year 2010
 
Description LSST:UK membership 
Organisation LSST Corporation
Country United States 
Sector Charity/Non Profit 
PI Contribution Gained Affiliate PI status in the LSST:UK consortium. I have a new student looking at LSST prospects for X-ray binaries.
Collaborator Contribution See above.
Impact Outcomes expected within the next two years, leading up to the survey.
Start Year 2016
 
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 eROSITA external collaborator 
Organisation Max Planck Society
Department Max Planck Institute For Extraterrestrial Physics (MPE)
Country Germany 
Sector Academic/University 
PI Contribution Gained eROSITA external collaborator to study a large survey with the space mission.
Collaborator Contribution See above.
Impact Outcomes expected this year.
Start Year 2017
 
Description Commentary for public non-expert audience published in Nature. 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Commentary provided as external expert, for a world-wide readership. Generated a lot of discussion, twitter retweets and email discussions etc. For example, here is a quote from Southampton's press officer:

"Hi Poshak,

Our media monitoring service picked up your comments to The Guardian regarding the visible black story -

http://www.theguardian.com/science/2016/jan/06/visible-light-black-holes-detected-for-first-time-v404-cygni

Regards,

Glenn"
Year(s) Of Engagement Activity 2016
URL http://www.nature.com/nature/journal/v529/n7584/full/529028a.html
 
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 International Press Releases following high impact article 
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 Multiple international press releases following the Nature Astronomy article. There was wide coverage including Daily Mail, Independent, lots of online science portals. Southampton link below in below. In addition, see NASA: https://www.nasa.gov/feature/jpl/nustar-probes-black-hole-jet-mystery/
Year(s) Of Engagement Activity 2017
URL https://www.southampton.ac.uk/news/2017/10/black-hole-jets.page
 
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 AAS Press Release
Year(s) Of Engagement Activity 2017
URL http://www.southampton.ac.uk/news/2017/01/southampton-researchers-view-black-holes.page
 
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 Press release on black hole research 
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 Media (as a channel to the public)
Results and Impact International press release from NASA. This did particularly well in terms of international reach. Here is a quote from Southampton's media officer:

"Hi Poshak,

Our media monitoring service has picked up a good amount of global media coverage for the clumpy black hole study we press release, pleased see attached. The items had a potential audience of over 104 million views.

As well as specialist space and science outlets, it was good to see the story appearing in mainstream news outlets such as the Daily Mail (over 60 million unique views to their website) and in today's Daily Express -

http://www.express.co.uk/news/science/631371/REVEALED-Inside-heart-galaxy-guzzling-supermassive-black-hole-NASA-Hubble

Times of India - http://timesofindia.indiatimes.com/home/science/Dust-doughnut-around-massive-black-hole-is-clumpy-study-shows/articleshow/50231972.cms

Astronomy magazine - http://www.astronomy.com/news/2015/12/nustar-finds-clumpy-doughnut-around-black-hole

Regards,
Glenn"
Year(s) Of Engagement Activity 2016
URL http://www.jpl.nasa.gov/news/news.php?feature=4798
 
Description Press release related to launch of Hitomi 
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 Media (as a channel to the public)
Results and Impact Press release mentioning my involvement in the Hitomi mission, which was recently launched.
Year(s) Of Engagement Activity 2016
URL http://www.southampton.ac.uk/news/2016/02/poshak-gandhi-astroh-space-telescope.page
 
Description Public talk at Pint of Science 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Pint of Science annual festival talk
Year(s) Of Engagement Activity 2017
URL https://pintofscience.co.uk/event/black-holes-and-revelations
 
Description Specialist workshop 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact RAS specialist discussion meeting on X-ray astronomy strategies.
Year(s) Of Engagement Activity 2017
URL https://sites.google.com/site/ukxrayastro/
 
Description TORUS 2015 workshop 
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 We led the organisation of an international workshop celebrating 30 years of supermassive black hole unification research. We had 104 participants from all over the world. In addition, we engaged with about 60 members of the general public in an outreach event with a mobile planetarium and explaining black holes.
Year(s) Of Engagement Activity 2015
URL http://torus2015.sungrazer.org/
 
Description Workshop on Simultaneous Multiwavelength Astronomy 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I was one of the primary organisers of a workshop with high level directors and personnel of many observatories to tackle the difficult issue of closely coordinating observations worldwide. There was intense discussion on the best mode to achieve cooperation, and this is beginning to influence policy, with some observatories offering new modes of coordination.
Year(s) Of Engagement Activity 2015
URL https://lorentzcenter.nl/lc/web/2015/713/info.php3?wsid=713
 
Description Workshop organiser at EWASS2015 
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 Co-organiser of a workshop on mid-infrared studies of galaxies at the large European Week of Astronomy and Space Science (EWASS) 2015.
Year(s) Of Engagement Activity 2015
URL http://eas.unige.ch/EWASS2015/session.jsp?id=Sp4
 
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