Fermi Finds “Transformer” Pulsar

Astronomers often liken the orbits of binary stars to a kind of dance, as the two partners swing around their mutual center of mass. But such partnerships can prove more hostile if one of the partners is a pulsar — the compact, rapidly rotating remnant of a star that went supernova.

Pulsar Suck Matter of its Companion Star NASA-Dana Berry

An artist's rendering of a pulsar sucking matter off its companion star.
NASA-Dana Berry

After the initial explosion, pulsars’ magnetic fields have them spewing beams of high-energy photons and relativistic particles. Typically these emissions weaken over time, ultimately leaving nothing but a dim stellar corpse. However, if the pulsar is part of a binary system, then it can suck the material off its companion star, spinning itself up like a ball hit with water from a hose and blazing with radiation again. These resurrected pulsars have rotational periods on the order of milliseconds, and their radiation is sometimes powerful enough to evaporate their companion stars.

Black widows, vampire zombie stars . . . however you spin it, these rapacious pulsars can spell the demise of their binary partners.

A recent study using the Fermi Gamma-ray Space Telescope has revealed one such system in a rare transitional phase. Fermi has proved pivotal in finding millisecond pulsars, since the gamma rays produced by these pulsars are energetic enough to shine through the obscuring material of the evaporating companion, whereas other radiation might be masked.

When the pulsar reaches a fast enough spin rate, the pressure of its relativistic jets prevents the infall of more material from the companion star, explains Roger Romani, who wrote Sky & Telescope’s cover story on black widows last November. The recently spotted “transformer” pulsar, PSR J1023+0038, is probably passing between the accretion and radio wind phases. Astronomers think J1023 is similar to a pulsar in a binary system 19,000 light-years away that underwent a powerful X-ray burst a few months prior. J1023 is only 4,400 light-years away, providing researchers a unique opportunity to study this transition process.

You can read more about the so-called “transformer” pulsar in the NASA press release or in the team’s paper.