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First White Dwarf That Acts Like Pulsar Discovered by Astronomers

By John Almirante, | February 09, 2017

The Binary System AR Scorpii as Depicted by Artists

The Binary System AR Scorpii as Depicted by Artists

Astronomers have found a white dwarf pulsar.  This is the first time that a white dwarf that acts like a pulsar has been discovered.

The binary system AR Scorpii (AR Sco) was found to contain the white dwarf pulsar.  It is located 380 light-years away in the constellation of Scorpius. As a pulsar, the small white dwarf, which is all that remains of a star, still sweeps its red dwarf companion with energetic radiation.

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 As it spins approximately every 2 minutes, the remnant of a star, located in the AR Scorpii system, strikes its celestial neighbor with beams of radiation. Previously, pulsars were all thought to be neutron stars.  Astronomers were finally able to detect a pulsar that was not a neutron star but a white dwarf.  This was the first white dwarf pulsar discovered after half a century of searching for pulsars.

Professors Tom Marsh and Boris Gänsicke at the University of Warwick's Astrophysics Group together with Dr. David Buckley from the South African Astronomical Observatory, made the discovery.  Their description of the novel binary system was published in the journal Nature Astronomy.

Neutron stars and white dwarfs are similar.  They are both remnants of stars that have collapsed. They are what is left of dead stars, their cores.  The difference between them is that neutron stars were formed from much larger, more massive stars while white dwarfs were once stars similar to the size of our own Sun.

Pulsars are similar as well to neutron stars and white dwarfs.  They are also the remains of stars.  Their difference is that they emit focused beams of radiation from their poles as they spin. Astronomers detect pulsars usually by observing the beam discharged by the spinning neutron star.  AR Sco's white dwarf pulsar however was detected by observing the periodic brightening and dimming of the red dwarf companion caused by the beam of radiation striking the dimmer object.

Every two minutes, the electrons in the atmosphere of the red dwarf is accelerated to almost the speed of light when it is struck by the beam of radiation from its celestial companion as it spins on its axis.  This results in changes in brightness of the dimmer object which can be observed from Earth, timed to the rotational period of the white dwarf.

AR Sco's white dwarf is 200,000 times more massive even though its dimensions are similar to Earth's.  Its red dwarf neighbor is a third of our sun's mass. The white dwarf rotates on its axis every 1.94 minutes.  It orbits the red dwarf every 3.6 hours at a distance of 1.4 million kilometers which is just three times the distance between the Earth and our moon.

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