Astronomers have discovered a new and unusual type of binary star lurking in our corner of the universe: one where a tiny white dwarf appears to blast its companion star with a beam of electrons every two minutes.
AR Scorpii, originally believed to be a single star in the Scorpius constellation, is about 380 light-years from Earth.
Using multiple telescopes, including the ESO’s Very Large Telescope in Cerro Paranal, Chile, and the Hubble Space Telescope, astronomers discovered that AR Scorpii isn’t a single star, but two: a white dwarf and a red giant orbiting each other every 3.6 hours “in a cosmic dance as regular as clockwork,” says the ESO.
White dwarfs are the remnants of older stars that have long since shed most of their mass. The remaining core is about the size of Earth, but with 200,000 times its mass. The red giant, in contrast, is a large, cool star with about one third the mass of our Sun.
AR Scorpii’s white dwarf spins so quickly that it whips electrons out into space almost to the speed of light, releasing radiation in the form of beams that rotate in a fashion similar to a lighthouse lantern.
Every time the beam passes through the red giant — every 1.97 minutes — the red giant is charged with energy, increasing its brightness by a factor of four within 30 seconds. The ESO said this behaviour was “unlike anything they had ever encountered.”
These pulses include radiation at radio frequencies, which astronomers said has never been seen before in a white dwarf. Similar versions have been observed in neutron stars — cores of long-dead stars smaller and denser than even white dwarfs.
“Just how AR Scorpii works is a bit of a mystery,” lead researcher Tom Marsh told CBC News, adding that multiple factors, including how fast the white dwarf is spinning or how powerful its magnetic field is, might be at just the right levels for this previously unseen phenomenon to occur. “That would be my best guess at the moment, but this is one of many open questions.”
As for anyone who looked at the artist’s rendition of AR Scorpii and saw similarities to the Starkiller Base in Star Wars: The Force Awakens, you might be assured (or dismayed) to learn that the white dwarf’s beam would theoretically prove as deadly as a sci-fi superlaser — albeit with a shorter range.
Coming into contact with the beam “would be distinctly unpleasant, as in terminal, for any inhabitants if they were as close as the cool star is … the surface would be heated to thousands of degrees in a matter of seconds. On a longer timescale the planet would be vaporized. If you are as far away as us, there is no problem, of course.”
While AR Scorpii was discovered over 40 years ago, astronomers originally classified it as a variable star. These stars can dip or rise in brightness due to a range of factors: some expand and contract, while others have orbiting objects like planets that obscure fractions of the light that we can observe from Earth.
In 2015 a group of amateur astronomers noticed that AR Scorpii’s variances were unusual and erratic, prompting renewed observation together with professional astronomers, led by Marsh.
Marsh told CBC News that “radically better” modern equipment helped to discover AR Scorpii’s true nature. “What couldn’t have been known then was its extraordinary emission at so many wavelengths because the satellites we used were not around then [when it was first discovered].”(Jonathan Ore, CBC News)
link: http://www.cbc.ca/news/technology/binary-star-mystery-ray-1.3699703
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