On June 1st, a SpaceX Falcon 9 rocket will carry supplies and new instruments to the ISS, including one designed to observe some of the strangest objects in the universe: neutron stars or pulsars. The Neutron Star Interior Composition Explorer (NICER) will be installed outside the ISS, where it will look for and study the extremely dense objects. Neutron stars begin their lives as stars around seven to 20 times the mass of our sun. When they collapse and cause a supernova explosion, they turn into a sphere that's only 12 miles across, with twice the mass of our sun squeezed inside. They're also called "pulsars" when they rotate hundreds of times per second.