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A Triggered Spring: Three Glitches in a Silent Pulsar ✛

Original: "Discovery of Three Glitches in the previously quiet pulsar PSR J1637$$-$$4642"
· Zhaoyi Wang, Chuwen Zheng, Yuhong Zhuang, Hanyu Zhang, Peng Liu, Zhonghao Tu, Ang Li
arXiv:2608.19555v1 · 2026-08-20 · CC BY 4.0 · 3 min
High Energy Stellar Nuclear Theory
A pulsar that spun steadily for decades suddenly produced three frequency jumps of different sizes — revealing details of its superfluid interior.

Pulsar PSR J1637−4642 is like a drum with a ratchet: it spins at enormous speed, and each radio flash is a click marking time. For nine and a half years, astronomers listened to this rhythm on the 64-meter Murriyang telescope in Australia, and heard not a single skip. The mechanism seemed to work flawlessly. But in 2020, the drum slipped: the rotation frequency jumped by 2.7 parts per million. That's as if the second hand of a clock suddenly sped up by one ten-billionth of a second per year.

A frequency jump, a glitch, is a sudden acceleration of a pulsar's rotation, which then partially relaxes. Inside the star, a superfluid (a frictionless fluid) rotates independently of the crust, and when vortices unpin, they transfer their angular momentum to the crust.

Three years later, the drum clicked again, but 1200 times weaker. Another 2.7 years after that came a third click, of intermediate strength. Three glitches in five years is rare for a pulsar considered 'quiet.' The most powerful glitch allowed a look inside the star: after the jump, the frequency began to return, but only a small fraction recovered—1.5% of the jump, over a characteristic timescale of about 100 days. It's as if a spring released from a latch didn't snap back immediately but slowly crept back.

The vortex creep model, where superfluid vortices are pinned to lattice nuclei in the inner crust, explained the aftermath. The fit gave the superfluid moment of inertia fraction: 1.87% of the star's total moment of inertia. This value falls within the range expected for superfluid neutrons in the inner crust. Previously, no such estimate existed for this pulsar — because there were no glitches.

Moment of inertia is a measure of how hard it is to spin up or stop a rotating body. For a neutron star, it combines contributions from the crust and the superfluid. The measured fraction of 1.9% indicates that only a small part of the mass participates in the glitch.

Before this work, PSR J1637−4642 was thought not to glitch, despite its youth (about 41 thousand years) and high energy. Now it's clear: it was accumulating stress like a spring on a latch, and it slipped. There are no engineering applications for this knowledge: it's pure understanding of neutron star interiors. But each such slip is a window into the quantum hydrodynamics of superdense matter, which cannot be reproduced in a laboratory.

If the pulsar continues to be monitored, more glitches can be accumulated to test whether their size distribution follows a power law, as seen in other young pulsars. The drum keeps spinning, and each new click is a chance to hear how its interior is structured.

Whole graph →

The weakest glitch of this pulsar changed its rotation frequency by just 14 nanohertz — equivalent to a clock's second hand speeding up by one ten-billionth of a second per year.

\phi(t) = \phi_0 + \nu(t-t_0) + \frac{\dot{\nu}}{2}(t-t_0)^2 + \frac{\ddot{\nu}}{6}(t-t_0)^3
Taylor expansion of the pulsar's rotation phase up to the third term
\phi_g = \Delta\phi + \Delta\nu_p (t-t_g) + \frac{1}{2}\Delta\dot{\nu}_p (t-t_g)^2 + \sum_i \Delta\nu_d^i \tau_d^i \left[1 - e^{-(t-t_g)/\tau_d^i}\right]
Phenomenological glitch model: permanent jumps in frequency and its derivative plus exponential decays
\dot{\nu}_c(t) = -\frac{I_l}{I}\frac{\delta\omega e^{-t/\tau}}{\tau} + \dot{\nu}_0 + \ddot{\nu} t
The rate of change of the crust's frequency is the sum of an exponentially decaying response from the superfluid component and a linear trend
Scientists
Albert EinsteinBarry BarishKip ThorneRichard FeynmanRussell HulseJocelyn Bell Burnell
Concepts
pulsar glitch magnetar glitch