COSMOS consortium researchers exploiting DiRAC HPC Facilities have made progress towards ambitious milestones in five key inter-related areas: (i) extreme gravity, (ii) inflation and the early universe, (iii) cosmic microwave sky, (iv) dark energy and (iv) galaxy archaeology. In the limited space available, we highlight recent breakthroughs in general relativistic simulations of black holes and inflation.
On 11 February 2016, the LIGO Scientific Collaboration announced the ground-breaking discovery of a gravitational wave signal (GW150914) representing the first incontrovertible observation of a black hole binary system, as well as the most energetic event ever observed in the Universe. Given recent advances such as our innovative GRChombo AMR code, COSMOS Consortium researchers (several also LSC members) are well-placed to exploit these new scientific opportunities in gravitational wave astronomy. We have continued our long-standing industrial collaboration through the COSMOS Intel Parallel Computing Centre (IPCC) to improve our research codes in cosmology and general relativity; we have particularly focussed on GRchombo and improving performance on multi- and many-core (Xeon Phi) systems, following in the wake of our 2015 HPCwire Award. Intel has also responded to the demands of ever increasing dataset size by developing a powerful software defined visualisation framework, including the OpenSWR software rasteriser and the OSPRay parallel ray tracer and volume renderer, a program in which COSMOS IPCC is directly involved. These tools hves allowed us to create unprecedented real-time visualisations of our science results using several TB datasets. In 2016 we demonstrated the adaptive mesh capabilities of ParaView powered by OSPRay and OpenSWR by creating videos of GRChombo black hole mergers for two of the largest HPC conferences, International Supercomputing 2016 and Supercomputing 2016, as publicised in insideHPC
Inflation is now the paradigmatic theory of the early universe, providing a dynamical mechanism to explain the many features of our current cosmology. In particular, it explains why the universe is homogenous over cosmological scales. Nevertheless, can inflation begin in the first place, if the initial conditions are not homogenous? To answer this question requires a numerical approach, as solving the full GR equations is not possible for generic inhomogenous initial conditions. We attacked this problem with the state-of-the-art numerical relativity code GRChombo and the results are reported in arXiv:1608.04408. We found that high scale inflation is generically robust – it will inflate despite large inhomogeneities. More interestingly, we found that low scale inflation – preferred by many string theory phenomenological models – is not robust, failing to inflate in the presence of large scale but subdominant inhomogeneities.
One of the biggest unresolved problems in Einstein’s theory of gravity is the weak cosmic censorship conjecture, which posits that spacetime singularities are always hidden inside a black hole horizon. Since nothing can escape a black hole, the breakdown of Einstein’s theory at singularities would be ‘censored’ from the outside world. In our numerical work with GRChombo, we find that the conjecture appears to be false if space has four or more dimensions. For example, the late stages in the evolution of a rapidly spinning black hole in six spacetime dimensions is shown (left); this is a disk-like structure with a great deal of fractal microstructure – the thinner rings are connected by ever thinner membranes that ultimately lead to a ‘naked singularity’. Given these results in extra dimensions, it is clear that, if cosmic censorship is true, then it must be a property specific to the three-dimensional space that we live in; without this property, Einstein’s theory of general relativity could lose its predictive power.