White dwarf pulsar unlike anything ever seen

(Credit: Mark Garlick/U. Warwick)

Scientists have identified an exotic binary star system 380 light-years away as a white dwarf pulsar—the first of its kind to be discovered in the universe.

The new system, AR Scorpii (AR Sco), contains a rapidly spinning, burnt-out stellar remnant called a white dwarf, which lashes its neighbor—a red dwarf—with powerful beams of electrical particles and radiation, causing the entire system to brighten and fade dramatically twice every two minutes.

“AR Sco is like a gigantic dynamo…”

The latest research establishes that the lash of energy from AR Sco is a focused beam, emitting concentrated radiation in a single direction—much like a particle accelerator—something which is unique in the known universe.

AR Sco lies in the constellation Scorpius, a close neighbor in astronomical terms. Its white dwarf is the size of Earth but 200,000 times more massive, and is in a 3.6 hour orbit with a cool star one third the mass of the Sun.

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With an electromagnetic field 100 million times more powerful than Earth, and spinning on a period just shy of two minutes, the system produces lighthouse-like beams of radiation and particles, which lash across the face of the cool star, a red dwarf.

As the researchers previously discovered, this powerful lighthouse effect accelerates electrons in the atmosphere of the red dwarf to close to the speed of light, an effect never observed before in similar types of binary stars—the red dwarf is powered by the kinetic energy of its spinning neighbor.

The distance between the two stars is around 1.4 million kilometers—or three times the distance between the Moon and the Earth.

“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, says Boris Gänsicke of the University of Warwick’s Astrophysics Group.

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

Tom Marsh, professor in the University of Warwick’s Astrophysics Group, and David Buckley from the South African Astronomical Observatory are coauthors of the study in Nature Astronomy.

Source: University of Warwick