After a general introduction to neutron stars, I will discuss the special role of their inner crust. This region is characterized by the coexistence of a lattice of neutron-rich nuclei (clusters) and a gas of unbound neutrons. The unbound neutrons are supposed to be superfluid, which gives rise to remarkable phenomena, such as the famous glitches (sudden increases of the neutron stars rotation frequency) and changes in the stars cooling behaviour. However, making reliable predictions for the superfluid critical temperature and for the entrainment between the neutron gas and the clusters remains a challenging problem for nuclear many-body theory. From a theoretical perspective, there are some analogies between the neutron gas and ultracold Fermi gases in atom traps, which may help to make theoretical predictions for the superfluid neutron gas more reliable.
Michael Urban studied at the Technical University of Darmstadt (Germany), where he did his PhD in theoretical nuclear physics under the supervision of Prof. Jochen Wambach. In 2001, he obtained a fellowship of the Alexander-von-Humboldt foundation that allowed him to work with Peter Schuck at the Institut de Physique NuclÃ©aire (IPN) at Orsay (Univ. Paris-Sud, France) on superfluidity in ultracold atoms. In 2003, he got a permanent position as a CNRS researcher at IPN Orsay. Since then, while continuing his research on transport in ultracold Fermi gases, he has turned more and more towards the physics of neutron stars.