AR Scorpii

AR Scorpii (AR Sco) is a binary pulsar that contains a white dwarf and a red dwarf. It is the first "white dwarf-pulsar" to be discovered. The 3.56-hour period in AR Sco's light curve caused it to be misclassified as a Delta Scuti variable, but in 2016, this period was found to be the binary orbital period. In addition, the system shows very strong optical, ultraviolet, and radio pulsations originating from the red dwarf with a period of just 1.97 minutes. These pulsations occur when a relativistic beam from the white dwarf sweeps across the red dwarf, which then reprocesses the beam into the observed electromagnetic energy. At present, the white dwarf is not accreting significantly, and the system is powered by the spin-down of the white dwarf. The pulsar is about the same size as Earth.

AR Sco's unusual nature was first noticed by amateur astronomers.