CBHEO · Connecting numerical simulations of black holes with experiment and observations

Connecting numerical simulations of black holes with experiment and observations

Compact objects and black holes in particular have acquired an increasingly centre-stage role in many areas of contemporary physics. For example, compact objects are one of the most important source of gravitational waves whose direct observation with laser interferometers (LIGO, VIRGO, KAGRA or the space-based eLISA mission) is expected to provide us with unprecedented views of the universe. The possible formation of black holes in particle collisions is one of the avenues pursued in experiments at the LHC to probe physics beyond the standard model of particles. Theoretical modelling is mandatory in all these new directions of physics and has been the main focus of this CIG project. Gravitational waves are ripples in spacetime created by compact astrophysical objects analogous to the generation of waves when a stone is thrown into a pond of water. These waves propagate from their source, say two black holes orbiting each other, across the universe and eventually can reach our observatories on planet earth. These waves are measurable only using the most modern laser technology and even then the process relies heavily on waveform catalogues containing theoretical predictions for the waves' specific shape. In comparison with the other forces (electromagnetic, weak and strong nuclear forces), gravity is extraordinarily weak and physicists have conjectured intriguing scenarios to explain this feature in terms of extra dimensions. In these so-called TeV gravity scenarios, gravity would become the dominant interaction at microscopic distances and one of the most dramatic predictions of these theories is the possibility of generating black holes in particle collisions at the LHC. We have modeled black holes numerically in the context of these scientific questions and obtained the following results. 1) We have discovered a new classification scheme of black-hole binaries into three morphologies. Identification of a binary's morphology in gravitational-wave observations will reveal valuable information about how the system was formed millions or billions of years ago. 2) The formalism developed for this purpose employs an averaging technique that vastly increases the computational efficiency of its modelling. 3) Gravitational waveforms have been computed numerically, studied in data analysis and used to demonstrate their suitability for identifying wave signals in noisy data streams. 4) Neutron stars and black holes have been modelled in a generalization of general relativity known as scalar-tensor theory. The properties of the compact objects and gravitational-wave emission has been studied. 5) An instability involving rotating black holes and their surrounding gas known as superradiance has been explored numerically. 6) Ultra-relativistic collisions in four dimensions generate enormous amounts of gravitational waves but not in excess of about 50%, so that a fraction of unity of the total collision energy remains available for black-hole formation. 7) We have verified that the collision dynamics are independent of the colliding objects rotation rate in the ultra-relativistic limit. 8) We have developed a formalism that enables us to collide black holes in up to 10 spacetime dimensions which covers the relevant range for the application to TeV theories.

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