Angular collapse of dipolar Bose-Einstein condensates

We explore the structure and dynamics of dipolar Bose-Einstein condensates (DBECs) near their threshold for instability. Near this threshold a DBEC may exhibit nontrivial biconcave density distributions, which are associated with instability against collapse into "angular roton" modes. Here we discuss experimental signatures of these features. In the first, we infer local collapse of the DBEC from the experimental stability diagram. In the second, we explore the dynamics of collapse and find that a nontrivial angular distribution is a signature of the DBEC possessing a biconcave structure.