AR Scorpii: A Tumultuous Binary Star System Where A White Dwarf Is ‘Whipping’ Its Companion

A team of astronomers has, using the Very Large Telescope (VLT) in Chile, discovered an exotic binary star system made up of a rapidly spinning white dwarf and cool red dwarf about a third the mass of the Sun. What makes this system unique is a behavior that has never been observed in any other system before.

In this system — named AR Scorpii — the spinning white dwarf powers up electrons almost to the speed of light. This creates blasts of radiation that lash the companion red dwarf star, causing the entire system to “pulse” every 1.97 minutes.

This phenomenon creates pulses that range in frequencies from ultraviolet to radio — something that has never been detected from a white dwarf system.

“AR Scorpii was discovered over 40 years ago, but its true nature was not suspected until we started observing it in 2015,” Tom Marsh of the University of Warwick — lead author of a study published Wednesday in the journal Nature, said in a statement. “We realized we were seeing something extraordinary within minutes of starting the observations.”

When AR Scorpii was first discovered in the early 1970s, it was misidentified as a lone variable star, which is a star whose brightness, as seen from Earth, fluctuates — either due to intrinsic or extrinsic factors. Even now, when a star system has been correctly identified, scientists are not quite sure what the source of the electrons that are powered up by the white dwarf is.

“We've known pulsing neutron stars for nearly fifty years, and some theories predicted white dwarfs could show similar behavior,” co-author Boris Gänsicke, also from the University of Warwick, said in the statement. “It's very exciting that we have discovered such a system, and it has been a fantastic example of amateur astronomers and academics working together.”