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Details of Grant 

EPSRC Reference: EP/W005727/1
Title: TESTING GRAVITY AROUND BLACK-HOLES WITH THE LISA MISSION
Principal Investigator: Bhagwat, Dr S S
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department: School of Physics and Astronomy
Organisation: University of Birmingham
Scheme: EPSRC Fellowship
Starts: 01 October 2021 Ends: 30 September 2025 Value (£): 461,770
EPSRC Research Topic Classifications:
Cosmology Gravitational Waves
EPSRC Industrial Sector Classifications:
Related Grants:
Panel History:
Panel DatePanel NameOutcome
27 Jul 2021 Stephen Hawking Fellowship - R2 Interviews Announced
26 Jul 2021 Stephen Hawking Fellowship - R2 Interviews- Panel 1 Announced
Summary on Grant Application Form
Gravitational-wave astronomy presents us with an incredibly powerful tool to test our understanding of gravity. The state-of-the-art description of the behaviour of gravity is given by the general theory of relativity (GR). Although this theory has an elegant framework and has stood experimental verification in all the regimes where tests were performed, the theory remains untested by experiments/observations in several crucial regimes. There is a tension between the description in GR and quantum mechanics (which is another cherished and well-tested theory in physics). Further, GR cannot explain certain critical observation in cosmology, such as why the cosmological constant is fine-tuned. Therefore, testing GR is central to further fundamental physics.

I am interested in this broad umbrella of tests of gravity with gravitational wave data. In this UKRI Stephen Hawking fellowship, I plan to extract information on gravity close to the supermassive black holes by analysing the gravitational waves radiated when two black holes merge. Gravity around the black holes are the strongest gravitational fields we know and understanding it is central to the progress of several subfields of physics (such as quantum gravity and cosmology). My proposal has two parts to it -

The first part builds the infrastructure necessary to carry out a powerful test known as the 'black hole spectroscopy'. The gravitational waves emitted just after two black holes merge contains a set of discrete frequencies which act as a signature of the black hole in GR. Being able to measure them precisely confirms that these objects are indeed black holes and that the gravity around them is described by GR accurately. The data from an upcoming space-based gravitational wave observatory called LISA is especially suited for this test. Its data will allow us to extract these set of frequencies about 100-10,000 times better than the current gravitational wave facilities, making it ideal for precision tests. However, LISA data is also remarkably complicated to analyse on a technical level and active research is being conducted on various techniques to handle it optimally. This project is focused on understanding these complications and builds an infrastructure that enables us to conduct a precision black hole spectroscopy with the LISA data. This work will be a significant contribution to preparing for the LISA mission and the infrastructure built will be useful multiple future studies that assess and conduct tests of gravity with LISA data.

The second part of the project develops a new test that will probe a unique feature of the black holes. GR predicts that black holes of all mass behave similarly. For instance, the gravitational waves emitted during the merger of black holes that are a few times the mass of the sun and those emitted by the supermassive black holes at the centre of the galaxies should have similar morphology. However, we have not yet tested this feature observationally. The LISA instrument can probe a large range of black hole mass (~100-108 times the mass of our sun) making it optimal to test this feature of GR. I plan to design a novel test to tease out this feature from the LISA data.
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Organisation Website: http://www.bham.ac.uk