Astronomers announced today that they have discovered a new type of binary star, in which a rapidly-spinning white dwarf star sweeps powerful beams of particles and radiation over its companion red dwarf star, causing it to pulse across almost the entire electromagnetic spectrum from the UV to radio.
This artist’s impression shows AR Scorpii. In this unique double star a rapidly spinning white dwarf star (right) powers electrons up to almost the speed of light. These high energy particles release blasts of radiation that lash the companion red dwarf star (left) and cause the entire system to pulse dramatically every 1.97 minutes with radiation ranging from the ultraviolet to radio. Image credit: M. Garlick / University of Warwick / ESO.
In May 2015, amateur astronomers from Europe came across a star system that was exhibiting behavior unlike anything they had ever encountered.
Follow-up from an international team of amateur and professional astronomers, led by the University of Warwick, on several telescopes – the NASA/ESA Hubble Space Telescope, ESO’s Very Large Telescope, the William Herschel and Isaac Newton Telescope in the Canaries, the Australia Telescope Compact Array, and NASA’s Swift satellite – revealed its nature.
This star system, called AR Scorpii, lies in the constellation of Scorpius, approximately 380 light-years from Earth.
It comprises a white dwarf star, the size of our planet but 200,000 times more massive, and a cool M-type star (red dwarf) one third the mass of the Sun, orbiting one another every 3.6 hours.
In a unique twist, AR Scorpii is exhibiting some brutal behavior. Highly magnetic and spinning rapidly, the white dwarf accelerates electrons up to almost the speed of light. As these high energy particles whip through space, they release radiation in a lighthouse-like beam which lashes across the face of the red dwarf, causing the entire system to brighten and fade dramatically every 1.97 minutes.
These powerful pulses include radiation at radio frequencies, which has never been detected before from a white dwarf system.
“AR Scorpii was discovered over 40 years ago, but its true nature was unsuspected until we observed it last May,” said lead author Prof. Tom Marsh.
“We realized we were seeing something extraordinary within minutes of starting to observe it.”
The observed properties of AR Scorpii are unique. And they are also mysterious.
The radiation across a broad range of frequencies is indicative of emission from electrons accelerated in magnetic fields, which can be explained by the spinning white dwarf.
The source of the electrons themselves, however, is a major mystery – it is not clear whether it is associated with the white dwarf itself, or its cooler companion.
“We’ve known pulsing neutron stars for nearly 50 years, and some theories predicted white dwarfs could show similar behavior,” said co-author Prof. Boris Gänsicke, also from the University of Warwick.
“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.”
The research will be published this week in the journal Nature.
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T.R. Marsh et al. A radio pulsing white dwarf binary star. Nature, published online July 28, 2016; doi: 10.1038/nature18620
