Astronomers have long been intrigued by the rhythmic pulses of neutron stars, the dense remnants of massive stars that exploded in supernovas. Despite significant advances in understanding their origins, these unusual pulses have inspired some outlandish theories, including ancient civilizations trying to communicate with us.
Typically, these "heartbeats" occur with precise regularity, likely caused by spinning neutron stars emitting brief radiation bursts like cosmic lighthouses. However, some pulses have begun "glitching," or speeding up unexpectedly, complicating efforts to decipher their mysteries.
In a recent paper published in Scientific Reports, physicists introduced a new model that aligns with these odd behaviors. "More than half a century has passed since the discovery of neutron stars, but the mechanism of why glitches happen is not yet understood," said Muneto Nitta, a Hiroshima University professor and the study's corresponding author. "So we proposed a model to explain this phenomenon."
Previous theories suggested that "avalanches" of superfluid vortices—highly unstable components of neutron stars seeking equilibrium and triggering chain reactions—might explain these glitches. However, the initial trigger for these avalanches is still debated.
"In the standard scenario, researchers consider that avalanches of unpinned vortices could explain the origin of glitches," Nitta explained. "Without pinning, the superfluid releases vortices individually, allowing smooth adjustments in rotation speed. There would be no avalanches and no glitches."
"But in our case, we didn't need any mechanism of pinning or additional parameters," Nitta added. "In this structure, all vortices are connected in clusters, so they can't be released one by one. Instead, the neutron star must release many vortices simultaneously."
The team proposed the presence of two interacting types of superfluid that might account for this strange behavior. Their model closely matches the observed data.
"Our model explains these glitches through quantum vortex networks at the interface of two different superfluids in neutron star cores," the paper states.
Despite this progress, many questions remain, reflecting the complexity involved. "A neutron star is a very particular situation where astrophysics, nuclear physics, and condensed matter physics converge," Nitta noted. "Observing them directly is challenging due to their distance, so we must deeply connect interior structures with observational data."
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