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Pulsating white dwarf described as a 'dynamo' found, no, not in the back pages, 380 LY away

Astroboffins have searched for magnetic neighbor for 50 years

By Iain Thomson, 8 Feb 2017

Fifty years after pulsars were discovered, scientists in the UK and South Africa have spotted the first white dwarf that mimics the emissions of a neutron star.

Collapsed star AR Scorpii (AR Sco), spotted 380 light years away by a team from the University of Warwick and the South African Astronomical Observatory, is about the same size as Earth but has 300,000 times the mass. Every 3.6 hours it orbits a companion red dwarf star about a third the size of our sun at a distance of 1.4 million kilometres (869,920 miles).

"AR Sco is like a gigantic dynamo: a magnet, size of the Earth, with a field that is ~10,000 [times] stronger than any field we can produce in a laboratory, and it is rotating every two minutes," said Professor Boris Gänsicke. "This generates an enormous electric current in the companion star, which then produces the variations in the light we detect."

As it turns, AR Sco sends out a powerful stream of particles and radiation that smashes into the red dwarf twice every two minutes. This stream accelerates electrons in the atmosphere of the red dwarf to close to the speed of light, providing kinetic energy to power its spin.

"The new data show that AR Sco's light is highly polarized, showing that the magnetic field controls the emission of the entire system, and a dead ringer for similar behavior seen from the more traditional neutron star pulsars," said Professor Tom Marsh.

The peculiarities of the star, published in the journal Nature Astronomy, make it a unique specimen so far. While there wasn't thought to be a theoretical reason why white dwarfs couldn't be pulsars, actually finding one for the first time confirms the theory.

AR Sco can now join the ranks of mapped pulsars that could one day form a natural type of GPS navigation for interstellar travel. Since pulsars don't vary their output significantly, they can be used for positioning, and Earth's location is mapped out using pulsars on Voyager's golden record. ®

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