Discovery of Three Glitches in the previously quiet pulsar PSR J1637$-$4642

Deep in the cosmos, spinning like cosmic lighthouses, are neutron stars. These are the collapsed cores of massive stars that have exploded, leaving behind objects so dense that a single teaspoon of their material would weigh billions of tons on Earth. As they spin, they emit beams of radiation that sweep across the sky with the precision of a clock. For decades, astronomers have used these celestial timekeepers to test the laws of physics, but the most fascinating ones are the young, energetic stars that sometimes behave erratically. Occasionally, a neutron star will suddenly speed up its rotation in a tiny, sharp jolt known as a glitch. This phenomenon is not a malfunction but a clue to the star's hidden interior. Scientists believe that inside these stars, a superfluid—a substance that flows without any friction at all—exists alongside the solid crust. When the solid crust slows down naturally over time, the frictionless superfluid inside keeps spinning at its original speed. Eventually, the two get out of sync, and the superfluid suddenly transfers some of its speed to the crust, causing the star to spin faster. By studying these glitches, researchers can peer inside a star they can never touch, learning about the strange state of matter that exists only under such extreme pressure.

For many years, one particular neutron star, known as PSR J1637–4642, was considered unusually quiet. Discovered in a survey using the Parkes radio telescope in Australia, this young star had been monitored regularly for over a decade without showing any signs of these sudden speed-ups. It was part of a group of pulsars that seemed to spin down smoothly, offering no dramatic events to study. However, a new analysis of data collected between 2009 and 2024 has overturned this calm picture. Researchers have now discovered that this "quiet" star actually experienced three distinct glitches during that period. The first and most powerful event occurred around early 2019, where the star's rotation frequency jumped by a tiny but measurable amount. Two smaller, more subtle jumps followed, one in 2022 and another in 2024. The fact that these events were found in a star previously thought to be inactive suggests that even the most placid neutron stars can harbor significant internal activity, waiting for the right moment to release built-up stress.

The team behind this discovery, based at Xiamen University in China, spent years refining the data from the Parkes telescope, which is now called Murriyang. They had to carefully sift through years of observations, accounting for changes in the telescope's equipment and filtering out interference from Earth's own radio signals. Their work revealed that the first glitch was a major event, causing a sudden increase in the star's spin rate that was roughly a million times larger than the other two. Following this big jump, the star's rotation did not immediately settle back to its old pace. Instead, it showed a slow, exponential recovery over a period of about 100 days, gradually easing back toward a new, slightly faster rhythm. The two smaller glitches, by contrast, were so subtle that the star's rotation appeared to jump to its new speed and stay there immediately, with no detectable slow-down afterward. This difference in behavior gave the scientists a unique opportunity to model what was happening inside the star.

By applying a physical model that describes how a superfluid moves through the star's interior, the researchers were able to estimate the size of the superfluid region involved in the big glitch. Their calculations suggest that the portion of the star's interior that participated in the speed-up accounts for about 1.9 percent of the star's total mass. This fraction aligns perfectly with theoretical predictions for a layer of superfluid neutrons located just beneath the star's solid crust. The model also indicated that the star's internal temperature is likely around one hundred million degrees, a value consistent with how old the star is and how it has cooled over time. The fact that the star showed a permanent increase in how quickly it was slowing down after the glitch further supports the idea that the superfluid and the crust had become permanently reconnected in a new way.

This discovery challenges the simple idea that neutron stars build up stress in a predictable, steady way before glitching. If that were true, one might expect glitches to happen at regular intervals or with similar sizes. Instead, PSR J1637–4642 waited nearly ten years in silence, then released three events of vastly different magnitudes in quick succession. The largest event was a thousand times bigger than the smallest one, and they happened at irregular times. This suggests that the process triggering these glitches is complex and perhaps somewhat random, depending on the intricate and chaotic interactions deep within the star's core. While the researchers cannot yet predict when the next glitch will happen, their work proves that even stars that appear calm on the surface are dynamic and active on the inside. The study reinforces the standard view that neutron stars contain superfluids and that these fluids are the key to understanding the violent, sudden changes in rotation that astronomers observe across the galaxy.