Neutron stars and gravitational waves
When massive stars run out of nuclear fuel, they explode in a gigantic supernova. What remains is a neutron star - an extremely compact heavenly body. This compactness makes neutron stars into potentially very effective sources for gravitational waves. This is true already for their creation: The image on he left shows a computer simulation of the collapsing core region of a supernova; the brightness of a region denotes its density. The extremely dense matter undergoing acceleration in an asymmetric explosion and collapse leads to the emission of gravitational waves.