Answer:
radio waves
Step-by-step explanation:
In the summer of 1967, U.S. Air Force officer Charles Schisler was on radar duty at Clear Air Force Base in Alaska when he noticed a fluctuating radio source. The source appeared over the course of several days, and Schisler noticed that its position coincided with the Crab Nebula. However, the findings weren't published by the Air Force at the time, and the discovery went unrealized until 2007. Astronomers in Puerto Rico discovered the same pulsing radio source. Determined to be a pulsar, the object is a rapidly-rotating, town-sized star that flashes about 30 times a second. Known as NP0532, or the Crab Pulsar,