Gravity is a familiar force, and central to astrophysics. Our best theory of gravitation is Einstein's general relativity (GR). This tells us that gravity is the bending of spacetime by matter. I am working on finding out what we could learn from observations of strong gravitational fields, where the curvature of spacetime is greatest. Of particular interest to me is what we may be able to learn by measuring gravitational waves (ripples in spacetime) with the proposed evolved Laser Interferometer Space Antenna (eLISA). I would like to know both what we could learn about astrophysical objects, such as black holes or neutron stars, from gravitational tests, and what we may be able to learn about the nature of gravity itself. More detailed information can be found in my publications or from my group's webpage.
One of the main sources of gravitational waves for LISA will be extreme-mass-ratio inspirals (EMRIs). These form when a compact object, such as a neutron star or stellar mass black hole, spiral into the supermassive black hole found in the centre of a galaxy. As the compact object orbits, it generates gravitational waves. These carry away energy and momentum, making the orbit shrink, as well as encoding information about the shape of the spacetime. The mass of the compact object is about a solar mass, while the supermassive black hole can be a million solar masses. This extreme mass-ratio means that the inspiralling object can be treated as a test particle in the background spacetime of the central black hole. It is this property that makes EMRIs a tantalising probe of black hole spacetime.
EMRIs are a popular area of research. I am looking at extreme-mass-ratio bursts (EMRBs): these are produced when the orbit is highly elliptical, so a single burst of radiation is emitted at the point of closest approach. EMRBs may evolve into more familiar EMRIs if the compact object returns on its orbit. I am particularly interested in finding out if we could learn anything about the massive black hole in the centre of our own galaxy from EMRBs. To do this I have been working on calculating how much information can be encoded in a burst, and how frequently we could expect a burst to be produced.
Alternative theories of gravity
General relativity has passed every observational test so far. However, these tests have all been in the weak-field regime, and it is possible we could discover new effects in strong fields. I have therefore investigated what differences might be observed in an alternate theory of gravity: f(R)-gravity. This is one of the simplest extensions to GR. For the class of theories I studied, I concluded that laboratory tests are more sensitive than astrophysical ones, although both are useful as they probe different regions.