After a 50-year search, an astrophysics team at the University of Warwick has finally discovered a white dwarf pulsar. This elusive object is the first of its kind to be discovered and is part of a binary star system that is only 380 light-years from Earth.
Normal pulsars are typically neutron stars, the ultra-dense cores of stars that remain after a supernova. These cores collapse in on themselves into a form so compact that protons and electrons merge to form neutrons. A typical neutron star has a 20-kilometer radius and an enormous gravitational pull. Some neutron stars bend light so much that astronomers can see the far side of the star.
This white dwarf, named AR Scorpii (AR Sco), is slightly less dense and larger than a typical neutron star, though of course that is a relative thing. This white dwarf pulsar is about the size of Earth, but is 200,000 times more massive. Although it can’t quite bend light enough for astronomers to see its far side, you still wouldn’t want to get too close due to the hyperfocused beams of radiation it emits and its immense gravitational pull. White dwarfs like AR Scorpii form when the outer layers of an averaged-size star similar to our sun shed its outer layers into a planetary nebula.
Binary Star System
The above video zooms in on imagery taken by the Hubble Space Telescope, which assisted in observations of the binary star system in which the white dwarf pulsar resides. AR Scorpii is in the constellation Scorpius.
The other star in this binary star system is a red dwarf that is only 1.4 million kilometers away from the white dwarf pulsar. They orbit a common center of gravity every 3.6 hours. Meanwhile, the white dwarf pulsar excites molecules in the red dwarf star as it rotates about every two minutes and hits the red dwarf with a focused radiation beam twice during each rotation. This accelerates electrons in the red dwarf’s atmosphere to near lightspeed.
Professor Boris Gänsicke, one of the two research team leaders, commented on the immense dynamo effect generated by AR Scorpii: “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. This generates an enormous electric current in the companion star, which then produces the variations in the light we detect.”
In essence, the red dwarf appears to pulse over a wide range of the electromagnetic spectrum, from ultraviolet to radio waves, due to AR Scopii’s dynamo effect. This was first detected by a team of amateur astronomers in Germany, Belgium and the UK in May of last year and the University of Warwick team followed through to determine the nature of the system using telescopes from around the world and in orbit that included the Hubble Space Telescope, the William Herschel Telescope, the European Southern Observatory’s Very Large Telescope in Chile, and the Australia Telescope Compact Array at the Paul Wild Observatory in Narrabri, Australia. Although white dwarf pulsars were theoretically possible, the surprise discovery of AR Scopii’s nature was the first time it was observed.