A twisted tale of a possibly precessing pulsar

Spinning neutron stars—pulsars—often emit jets of material along their rotation axis. The jets of the Vela pulsar, however, are extraordinary. A decade ago, a series of Chandra X-Ray Observatory images suggested that the Vela jet had a dynamically changing shape. But the images were erratically spaced in time and not of sufficient quality to give a reliable picture of jet evolution. Now a new Chandra team led by George Pavlov (Pennsylvania State University) and Oleg Kargaltsev (George Washington University) has collected additional images such as the one shown here—enough images to create a video of an evolving, twisting jet. Moreover, the team reports that the details of the jet morphology are well described by a simple model that assumes the Vela pulsar is precessing with a period of 120 days and that the jet particles are ballistically emitted along the periodically changing rotation axis. Although suggestions of precessing pulsars exist in the literature, no such pulsars have been confirmed. Indeed, a twisting, Vela-like jet can result from the unstable growth of density perturbations within a jet, so additional observations and analysis will be needed to confirm Vela's apparent precession. No external objects are seen to exert torques on the Vela pulsar. So if the precession picture holds up, the neutron-star matter distribution must not be spherically symmetric. Detailed analysis of the precession could provide information about how the matter is distributed. And if the Vela pulsar is indeed a massive, rapidly rotating, nonspherical object, it might be a copious source of detectable gravitational waves. (M. Durant et al., Astrophys. J. 763, 72, 2013.)—Steven K. Blau