'Transformer' Pulsar is More Than Meets the Eye

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Astronomers may have not yet found Cybertron but this “transforming” pulsar definitely has a shape-shifting double personality.

Using NASA’s Fermi Gamma-Ray Space Telescope, an international team of researchers has observed a peculiar type of binary star system named AY Sextantis that consists of a rapidly-spinning millisecond pulsar — that is, a bright radio-beaming neutron star, the compacted corpse of a dead star that’s since gone supernova — with a larger, low-mass star.

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The dense neutron star periodically slurps up material from its swollen companion as the two whirl around each other every 4.8 hours, but when too much material from the low-mass star crowds the accretion disk surrounding the neutron star it gets hot enough to glow in x-ray wavelengths.

At this point turbulence in the disk at a mere 50 miles above the surface of the spinning neutron star gets the superheated material caught up in powerful magnetic fields. The radio beacons are snuffed out as jets blast from the star’s poles, crackling with gamma rays… AY Sextantis has transformed from a low-mass X-ray binary to a transient, compact, low-mass gamma-ray binary.

“It’s almost as if someone flipped a switch, morphing the system from a lower-energy state to a higher-energy one,” said Benjamin Stappers, astrophysicist at the University of Manchester, England, and lead on the research team. “The change appears to reflect an erratic interaction between the pulsar and its companion, one that allows us an opportunity to explore a rare transitional phase in the life of this binary.”

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With such close proximity and rapid orbital period, the pulsar will soon completely dismantle its larger companion through its intermittent but energetic feeding periods.

Watch the video for an illustration of how this complex process is thought to occur:

Named PSR J1023+0038 (J1023 for short) the pulsar was first discovered in 2007 by Anne Archibald, a postdoctoral researcher at the Netherlands Institute for Radio Astronomy. It’s located about 4,400 light-years away in the southern constellation Sextans.

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J1023 is helping astronomers determine how other, more distant pulsars shift from x-ray to gamma ray emissions, as well as how millisecond pulsars develop their incredible rates of rotation.

The findings were published in the July 20 edition of The Astrophysical Journal.

Video credit: NASA Goddard Space Flight Center. Source: NASA