Gravitational Physics

Members: David Alonso and Pedro G. Ferreira

The past few years have seen a dramatic increase in interest in gravitational physics and its mother theory, General Relativity. Fuelled by observations in cosmology with the cosmic microwave background and surveys of galaxies, in tandem with the discoveries coming from gravitational wave observatories as well as attempts at imaging and probing black holes at the centres of galaxies, there is now a world wide effort to learn as much as we can about gravitational physics in a wide range of regimes. Researchers at the BIPAC have been at the forefront of this research on a number of fronts.

Cosmological data is becoming sufficiently precise that it should be possible to test some of the fundamental assumptions that enter the standard model arising from General Relativity. We have developed a number of methods using the clustering and weak lensing of galaxies to constrain deviations from General Relativity and, more generally, allow us to constrain, or detect the presence of new forces that might emerge from new, unexpected, physics. Since 2016, this activity has been supported by an ERC Advanced Grant awarded to Pedro Ferreira.

On the same front, we have pioneered the use of galaxies as laboratories for fundamental physics. Galaxies are immensely rich and complex structures in which many different physical phenomena come into play. While the are very difficult systems to model, there is now a vast collection of well imaged galaxies, in a range of wavelengths, which can be used to disentangle different effects. We have pioneered the use of Bayesian forward modelling of such messy systems to come up with remarkably tight and robust constraints on gravitational physics and dark matter properties.

The detection of gravitational waves has opened a new window on to the Universe and has already led to tremendous progress in constraining new physics. We have used the observation of gravitational waves from the binary neutron star merger, GW170817, to greatly constrain possible extensions to General Relativity. Current work in the BIPAC is focussing on the production of gravitational wave during ringdown and how they might carry detailed information about the physics at play during merger. In tandem, there is an active research in numerical relativity trying to understand the accretion of relativistic fields on black holes and how they might affect the signals from binary black hole mergers.