Neutron stars are ultra-dense remnants of supernovae the size of a city. In the 1930s, Fritz Zwicky hypothesized their existence, and later Jocelyn Bell Burnell discovered pulsars — rapidly rotating neutron stars.
The edge of the supernova remnant RCW 86 is where the shock wave from a star's explosion slams into the surrounding gas. The IXPE telescope looked at the southwestern part of this boundary in X-rays and tried to catch polarization — the way these rays oscillate.