Black holes and axions stars
In the paper arXiv:1609.04724, shortly to be published in JCAP, we studied, for the first time, collapse of axion stars numerically using the full non-linear Einstein equations of general relativity and the full non-perturbative cosine potential. We identified three regions of the parameter space: i) long-lived oscillating axion star solutions, with a base frequency modulated by self-interactions, ii) collapse to a BH and iii) complete dispersal due to gravitational cooling and interactions. Using full 3+1 Numerical Relativity, many open problems which defy a perturbative approach can be solved, including the behaviour of the axion field around highly spinning black holes. I will briefly discuss the results in our paper and future directions.