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White dwarf strikes companion star with high-energy pulse

Scientists have known about AR Sco since the 1970s, but it was misidentified as a lone variable star.

By
Brooks Hays
An artistic rendering reveals the pulse of radiation sent from a white dwarf to its larger companion, a cool red dwarf. Photo by ESO
An artistic rendering reveals the pulse of radiation sent from a white dwarf to its larger companion, a cool red dwarf. Photo by ESO

COVENTRY, England, July 27 (UPI) -- Astronomers say they've never seen a star system quite like AR Scorpii, or AR Sco, a pair of stars orbiting each other within the constellation Scorpius.

Divided by an interval just less than two minutes, the system's red dwarf brightens and fades dramatically, over and over. A new study, published this week in the journal Nature, suggests the star's oscillating appearance is explained by its companion's aggressive tendencies.

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Though the red dwarf is much bigger than its companion, it's also cooler and less dense. It is roughly one-third the mass of the sun.

The spinning white dwarf, on the other hand, is about the same size as Earth, but 200,000 times more massive. It spins at a high velocity, accelerating a pulse of electrons toward its companion. The high-energy electrons generate a beam of radiation that slashes across the face of the red dwarf, causing the entire system to radiate.

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The radiation beam features a wide range of frequencies, suggesting the electrons are moving through a magnetic field. Scientists suggest the white dwarf and its super fast spin rate are likely responsible for the magnetic field, but they aren't sure where the electrons themselves are coming from -- the red dwarf or the white dwarf.

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Scientists have known about AR Sco since the 1970s, but it was misidentified as a lone variable star. The latest survey shows the binary star system is truly unprecedented.

"We've known pulsing neutron stars for nearly fifty years, and some theories predicted white dwarfs could show similar behavior," Boris Gänsicke, an astronomer at the University of Warwick, said in a news release. "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."

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