Astronomers Discover A White Dwarf-Red Dwarf Binary System That Behaves Like A Pulsar

Just 380 light-years from Earth lies a unique stellar object named AR Scorpii. Although this object, which consists of a rapidly spinning white dwarf and cool red dwarf about a third the mass of the sun, was discovered over 40 years ago, its true nature is only just being understood.

A team of researchers from the University of Warwick in the U.K. and the South African Astronomical Observatory, has, in a new study published in the journal Nature Astronomy, identified AR Scorpii as a white dwarf pulsar — the first such object ever detected.

Pulsars are rapidly rotating neutron stars, and were first discovered nearly 50 years ago. As a pulsar rotates, it emits high-energy radiation into the cosmic void, similar to a lighthouse, casting beams of light. If this beam of high-energy radiation is pointed toward the Earth, the pulsars can be detected using telescopes.

Something similar is happening with AR Scorpii. In this binary star system, the spinning white dwarf — a star that is estimated to be the size of Earth but 200,000 times more massive — 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 two minutes.

“The new data show that AR Sco’s light is highly polarised, showing that the magnetic field controls the emission of the entire system, and a dead ringer for similar behaviour seen from the more traditional neutron star pulsars,” study co-author Tom Marsh from the University of Warwick said in a statement.

AR Scorpii is emitting pulses that range in frequencies from ultraviolet to radio — something that has never been detected from a white dwarf system — and the entire system possesses an electromagnetic field 100 million times more powerful than that of Earth.

“AR Sco is like a gigantic dynamo: a magnet, size of the Earth, with a field that is ~10,000 stronger than any field we can produce in a laboratory, and it is rotating every two minutes,” co-author Boris Gänsicke, also from the University of Warwick, said. "This generates an enormous electric current in the companion star, which then produces the variations in the light we detect."