A pulsar that had been silent for roughly a decade suddenly revealed three distinct rotational glitches, including one that shifted its spin rate by nearly 3 parts per million. The discovery came from more than 15 years of observations at a single Australian radio telescope.
According to Phys.org, a team of astronomers led by Zhaoyi Wang of Xiamen University analyzed 15.5 years of data from the Murriyang radio telescope, collected between February 2009 and October 2024. Their paper was posted to the arXiv preprint server on Aug. 20 and has been accepted for publication in the Astrophysical Journal Letters.
Pulsars are neutron stars that spin rapidly and emit regular pulses of radio signals. PSR J1637-4642 is estimated to be about 41,000 years old, extremely young by cosmic standards. It spins once every 154 milliseconds. Despite its young age and relatively high energy output, it had never shown any glitches during roughly a decade of observations after it was first discovered.
That changed when the full dataset was examined. The first glitch appeared around 2018 and was the strongest of the three. The pulsar's rotation frequency jumped by about 17.54 microhertz, a fractional change of roughly 2.7 parts per million. A second, much smaller glitch arrived about three years later, shifting the frequency by only about 14 nanohertz. A third glitch appeared roughly 2.7 years after that, producing a frequency increase of about 179 nanohertz, placing it between the other two in strength.
Glitches in pulsars are not fully understood, but the leading explanation involves the interior structure of the neutron star. Astronomers think that a sudden transfer of angular momentum from a superfluid layer inside the star to its solid outer crust causes the crust to spin up abruptly, producing the jump in rotation rate that observers detect.
After the 2018 glitch, the pulsar did not snap immediately into its new rotation rate. Part of the change relaxed gradually over time. Modeling the aftermath suggested that about 1.9% of the neutron star's moment of inertia is tied to superfluid material in its inner crust, with a relaxation timescale of roughly 102 days.
"PSR J1637−4642 adds to the growing class of young pulsars that exhibit large glitches after extended intervals of apparent quiescence," the team wrote in the paper.
The case is notable because the pulsar's long quiet period before the first glitch, followed by two more glitches in relatively quick succession, adds data to a pattern that astronomers have been trying to understand. Young pulsars are generally expected to glitch more often than older ones, but the timing and spacing of glitches remains difficult to predict.
