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Dynamics of compact objects at the centre of galaxies and implications for gravitational wave detections

Project Description

Under the supervision of Dr Fabio Antonini, the student will develop a theoretical framework to make predictions for the gravitational wave sources produced in the nuclei of galaxies where dense nuclear star clusters are often observed.

The LIGO-Virgo detections have not only confirmed the existence of gravitational waves, but have also ushered astrophysics into a new era of observing cosmic events that were previously invisible. This new set of eyes on the Universe will provide important clues to the properties of compact objects such as black holes and neutron stars and to the environments in which they form. The development of a coherent theoretical understanding of the astrophysical processes leading to compact object coalescence is therefore required, which will enable scientists to analyse the large amount of new detections expected over the coming years by the advanced network of gravitational waves detectors.

Merging compact-object binaries can form as the result of: (i) the evolution of massive
binary stars in the field of a galaxy; (ii) dynamical interactions in the secular evolution of
globular clusters; and (iii) dynamical interactions in nuclear clusters (this project). We will
make the first precise prediction for scenario (iii), which we will use to establish whether
binary black hole mergers come predominantly from galactic nuclei, globular clusters or
the galactic field.

The specific objectives of the research proposal are:

1) Estimate the rate of coalescence and the properties of compact-object binaries forming in galactic nuclei. By combining numerical and analytical calculations, we will derive the physical properties of all compact object binaries potentially detectable by ground based interferometers like Advanced Ligo and Virgo. These include black hole masses, binary parameters, radial distributions, redshift distributions. Such properties will be used to characterise the populations of retained and ejected binaries. They will allow us to build a theoretical framework for the astrophysical interpretation of the large number of gravitational waves detections expected from Advanced Ligo in the next few years. Combined with additional and improved data on black holes X-ray binaries and ultra luminous X-ray sources in both globular and nuclear star clusters, it will be possible, for the first time, to constrain the relative importance of the different formation scenarios for black hole binaries.

2) Identify and characterise the dynamical processes that lead to the formation and merger of compact-object binaries in galactic nuclei with and without massive black holes. The dynamics of nuclei without black holes resembles that of globular clusters, while the dynamics of nuclei with massive black holes presents unique characteristics. Relativistic N-body simulations of nuclear clusters of both types will provide concrete predictions for merger rates as a function of nuclear parameters, thereby contributing to a new understanding of the physics of galactic nuclei.

3) Characterise compact binaries consisting of a black hole accreting from a stellar companion, thus becoming visible as an X-ray binary. By means of N-body and Monte Carlo simulations, we will model the formation and dynamical evolution of X-ray binaries progenitors. Comparison with available data will provide constraints on the number of stellar origin black holes in galactic nuclei. This number is so far completely unknown but is extremely important in the context of galaxy formation and evolution, as it provides limits on the possible growth of supermassive black holes from low mass seeds.

Astrophysics has entered a new Golden Age. Advanced LIGO and VIRGO are operational; new detectors such as KAGRA and LIGO India will soon come on line, and LISA will fly in 2030s. This project will provide a theoretical framework for the physical interpretation of this wealth of unprecedented new data.

This project will be funded by the STFC.
Applicants should apply to the Doctor of Philosophy in Physics and Astronomy with a start date of 1st October 2020.

In the research proposal section of your application, please specify the project title and supervisors of this project. If you are applying for more than one project, please list the individual titles of the projects in the text box provided. In the funding section, please select ’I will be applying for a scholarship/grant’ and specify that you are applying for advertised funding from the STFC.

Applicants will need to submit the following documents with their application:
- post high school certificates and transcripts to date
- academic CV
- personal statement
- two academic references. Your references can either be uploaded with your application, or emailed by the referee to or

Funding Notes

Tuition fee support: Full UK/EU tuition fees
Maintenance stipend: Doctoral stipend matching UK Research Council National Minimum

You should have obtained, or be about to obtain a First or Upper Second Class UK Honours degree in Physics , or a related subject, Alternatively, applicants with equivalent qualifications gained outside the UK will also be considered. Applicants with a Lower Second Class degree will be considered if they also have a Master’s degree.
Applicants whose first language is not English are normally expected to meet the minimum University requirements (e.g. 6.5 IELTS)

Related Subjects

How good is research at Cardiff University in Physics?

FTE Category A staff submitted: 19.50

Research output data provided by the Research Excellence Framework (REF)

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