ICTP-SAIFR/IFT-UNESP Physics Discussions

The first direct detection of gravitational waves was announced 5 years ago (about 1 graduate student generation).  The LIGO and Virgo Collaboration (which now includes KAGRA too) has recently updated their catalog of merging binaries of black holes and neutron stars: the catalog now contains a total of 50 events.In this talk I will give an overview of what gravitational waves are and how we observe them.  I will discuss the discoveries made over the past 5 years and how they help us learn about fundamental physics (tests of relativity; state of dense matter), astrophysics (origin of neutron star and black hole binaries; origin of certain elements), and cosmology.

The soil dwelling bacterium Myxococcus xanthus is an amazing organism that uses collective motility to hunt in giant packs when near prey and to form beautiful and protective macroscopic structures comprising millions of cells when food is scarce. I will present an overview of how these cells move and how they regulate that motion to produce different phases of collective behavior. Inspired by recent work on active matter and the physics liquid crystals, I will discuss experiments that reveal how these cells generate nematic order, how defect structure can dictate global behavior, and how they actively tune the Péclet number of the population to drive a phase transition from a gas-like flocking state to an aggregated liquid-droplet state during starvation.