Researchers have observed for the first time a white dwarf pulsar. Credit: The University of Warwick
Scientists have identified an exotic binary star system 380 light-years away as a white dwarf pulsar, the first ever discovered in the universe.
Researchers at the University of Warwick in the U.K. have identified the star AR Scorpii (AR Sco) as the first white dwarf version of a pulsar—objects found in the 1960’s and associated with very different objects called neutron stars.
AR Sco, which lies in the Scorpius constellation, contains a rapidly spinning, burnt-out stellar remnant called a white dwarf, which lashes its neighboring red dwarf with powerful beams of electrical particles and radiation, causing the entire system to brighten and fade dramatically twice every two minutes.
The latest research, conducted by professors Tom Marsh and Boris Gänsicke of the University of Warwick’s Astrophysics Group, with David Buckley, Ph.D., from the South African Astronomical Observatory, establishes that the lash of energy from the star is a focused beam emitting concentrated radiation in a single direction—similar to a particle accelerator—something that is unique in the known universe.
Marsh compared the new discovery with what was previously known about the universe.
“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,” he said in a statement.
According to the study, AR Sco shows strong linear polarization that varies strongly and periodically on both the spin period of the white dwarf and the beat period between the spin and orbital period, as well as low-level circular polarization.
The morphology of the modulated linear polarization is similar to what is seen in the Crab pulsar, but with a more complex waveform owing to the presence of two periodic signals of similar frequency.
The white dwarf is about 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.
The star also has an electromagnetic field 100 times more powerful than Earth and is spinning on a period just shy of two minutes, enabling AR Sco to produce lighthouse-like beams of radiation and particles, which lash across the face of the cool star, a red dwarf.
”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,” Gänsicke said in a statement. “This generates an enormous electric current in the companion star, which then produces the variations in the light we detect.”
Previous research showed the powerful light house 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. This enables the red dwarf to be powered by the kinetic energy of its spinning neighbor 1.4 million kilometers away.
The study was published in Nature Astronomy.
