Since its discovery, the pulsar PSR J1637−4642 had been considered quiet. However, over the past 15 years it has demonstrated as many as three rotational glitches. Such events are entirely normal for these objects, but their concentration forces scientists to think more deeply about the processes occurring inside neutron stars.
A “Quiet” Neutron Star
Based on observational data collected over more than 15 years with the Parkes radio telescope, astronomers detected three interruptions in the rotation of the pulsar PSR J1637−4642 — a young neutron star that had shown no signs of such events since its discovery. Among the three glitches was one that changed its rotation rate by nearly 3 parts per million. The scientists’ paper has been accepted for publication in The Astrophysical Journal Letters. This is reported by phys.org.
Pulsars are rapidly rotating neutron stars that emit regular pulses of radio signals. Some pulsars occasionally show a sudden increase in their rotation rate, known as a “glitch.” Younger pulsars tend to display this complex timing behavior more frequently, which is precisely why they are so interesting to study.
Although the exact cause of glitches remains unknown, astronomers believe that they are caused by a sudden transfer of angular momentum from superfluid matter inside the star to its solid crust.
PSR J1637−4642 is a pulsar about 41,000 years old, which is extremely young by cosmic standards. It rotates once every 154 milliseconds. Despite its young age and relatively high energy output, it remained “quiet” and showed no glitches for roughly a decade of observations after its discovery.
Three “Jumps” in the Pulsar’s Rotation
As part of this study, a team of astronomers led by Zhaoyi Wang of Xiamen University examined this young pulsar. They analyzed 15.5 years of data collected with the Murriyang radio telescope between February 2009 and October 2024.
The analysis revealed three clearly defined glitch events. The first occurred around 2018 and was the strongest. The pulsar’s rotation frequency suddenly increased by about 17.54 microhertz, corresponding to a relative change of approximately 2.7 parts per million.
The second glitch occurred about three years later and was smaller in scale. It changed the rotation frequency by only about 14 nanohertz. The third glitch appeared approximately 2.7 years after the second. It had an intermediate strength, causing an increase in frequency of about 179 nanohertz.
Long-Term Relaxation Recovery
After the first glitch, the pulsar did not immediately stabilize at its new rotation frequency. Instead, part of the change gradually relaxed over time. Modeling of the aftermath of this glitch showed that about 1.9% of the neutron star’s moment of inertia is associated with superfluid matter in its inner crust. The model also indicates a relaxation timescale of approximately 102 days.
These results are consistent with the long-standing hypothesis that frequency jumps are caused by a sudden transfer of angular momentum from superfluid neutrons inside the neutron star to its crust. The crust then abruptly accelerates, producing the sudden increase in rotation frequency observed as a glitch. After the glitch, the pulsar gradually returns toward equilibrium, while the inner crust and superfluid matter approach a new equilibrium state.
“Our results suggest that even ‘quiet’ pulsars can exhibit significant glitch activity,” the team concludes. The long period of silence before the first glitch may indicate that stress accumulated over many years before internal changes triggered the sudden acceleration in rotation.
