White dwarf blasts lighthouse-like beam at its red dwarf companion

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The observations revealed AR Scorpii, seen here in an artist's impression, to be an extraordinary binary system(Credit: M. Garlick/University of Warwick/ESO)

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Last year, a group of amateur stargazers noticed something a little strange about a distant star, and before long, a full study was launched, with multiple telescopes, including the European Southern Observatory's (ESO) Very Large Telescope (VLT) peering at AR Scorpii. What they found was a fascinating binary system, exhibiting never-before-seen behavior.

New observations of the star system have revealed it to be far more dramatic than was thought when the object was first studied more than 40 years ago. Rather than a single star, the researchers found that the system, which is located 380 light-years from Earth, is actually binary, playing host to a pair of stars orbiting one another.

The two stars are vastly different, with one being a red dwarf just one third the mass of the Sun, and the other a white dwarf roughly the size of Earth, but containing some 200,000 times more mass.

The observations also revealed that AR Scorpii is no ordinary binary system, but one that's exhibiting some fascinating and quite brutal behavior. The white dwarf is thought to be spinning at an extremely high speed, a process that's accelerating electrons close to the speed of light.

The researchers describe the release of radiation from the accelerated high-energy particles as being akin to a cosmic lighthouse, with the beam lashing across the surface of the companion red dwarf. Those intense pulses, which include radiation at radio frequencies – something that's never been observed with a white dwarf – cause a dramatic brightening and fading of the system every 1.97 minutes.

 The binary system lies in the constellation of Scorpius, some 380 light-years from Earth(Credit: Digitized Sky Survey 2. Acknowledgement: Davide De Martin)

While the rapid spinning of the object explains the broad range of radiation frequencies – its exactly what you'd expect to see with electrons being accelerated in magnetic fields – the actual source of the electrons is something of a mystery. As of yet, astronomers haven't been able to work out whether the electrons are originating in the white dwarf, or the much cooler red dwarf companion star.

AR Scorpii was first studied in the early 1970s. At that stage, astronomers looked up at the distant body, and watching its fluctuations in brightness, concluded that it must be a single star with internal properties that cause it to brighten and dim regularly.

In May 2015, a group of amateur astronomers from the UK, Germany and Belgium took another look at the system, and noticed its unusual behavior. Follow-up studies by researchers at the University of Warwick in the UK then characterized the distant star system, making use of multiple telescopes, including the VLT, and NASA's Swift and Hubble Space Telescope installations.

Full details of the international study that lead to the characterization of AR Scorpii are due to be published on July 28 in the journal Nature.

"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" said study co-authoer Boris Gänsicke.

Source: ESO

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