PSR 418-D/1015.3 was the Federation designation of a rogue pulsar discovered in sector 418-D on stardate 1015.3. The mar-Atyya religious group on planet Mestiko called this the Scourer, as the group believed that God would cleanse their world of unholiness through devastation by the pulsar.
This pulsar passed through the Mestiko system in 2265, causing massive destruction on the planet and the other bodies in the star system. Called "the Pulse" by the people of Mestiko, many saw the disaster as a fulfillment of prophecies. (TOS - Mere Anarchy eBook: The Darkness Drops Again)