Some 380 light years away in the constellation Scorpius lies a star that has puzzled astronomers for over 40 years. Called AR Scorpii, the star flashes brightly and fades again every couple minutes, like a lightbulb on a dimmer switch. Now, astronomers have identified the cause of the flickering, and it's a reminder that the cosmos is still rife with terrifying secrets.
Artist's impression of the exotic binary system AR Scorpii, with a compact white dwarf star (right) flogging its red dwarf companion with high energy electrons every two minutes. Image: M. Garlick/University of Warwick/ESO
AR Scorpii, previously identified as a single, variable star, is actually two, a compact white dwarf the size of the Earth but 200,000 times more massive, and a cool red dwarf a third the size of the Sun. By examining the system with the Very Large Telescope at the European Southern Observatory, the Hubble Space Telescope and others, astronomers have now learned that the white dwarf is spinning incredibly fast, charging up electrons to almost the speed of light.
As the white dwarf twirls about, these energised particles whip through space, lashing the the cooler companion and releasing a powerful pulse of electromagnetic radiation every 1.97 minutes.
This brutal star-on-star bondage, documented today in Nature, has not only never been seen before; it's never been imagined before. Pulsing has been observed in neutron stars, extremely dense objects formed by the gravitational collapse of a stellar remnant after a supernova. But while some theories have predicted that white dwarfs could act in a similar manner, the details of this system's behaviour — including the source of the electrons that charge up the cosmic floggings — remain an enigma.
"The strength of the pulsations are unprecedented," lead study author Thomas Marsh of the University of Warwick told Gizmodo in an email. "The high energy electrons are also very unusual — there is only one other system like this, and relativistic electrons are hard to understand when it comes to white dwarfs which generally do not show high-energy phenomena. I think this is what excites me most — it could be that we are seeing a new form of cosmic particle accelerator."
Marsh and his collaborators — a team that includes five amateur astronomers — are continuing to study the star closely across the electromagnetic spectrum, using the Very Large Array in New Mexico to and the XMM-Newton X-ray satellite to pick up radio and X-ray emissions, respectively. They're also hoping to resolve the structure of the mysterious electron beam. "So far it appears as a point source, but it may just be a matter of resolution," Marsh said.
Naturally, the discovery of AR Scorpii's true nature also astronomers wondering if there are more like it. Only time will tell. But while scientists continue to probe the violent mysteries of multi-star systems, the rest of us can go about our lives a bit more grateful for this mercifully pacifistic corner of the galaxy we're lucky enough to live in.