Long-term study of pulsar nulling in PSR J1048-3832 and others reveals evolving emission behaviour

Star system: PSR J1745-3040 | Distance from the Sun: 49141 light years

Pulsars are highly magnetised, rapidly rotating neutron stars — the ultra-dense remnants left behind when a massive star ends its life in a supernova explosion. They emit narrow beams of radio waves that sweep across space like a lighthouse, producing precise pulses detectable by radio telescopes on Earth. Some pulsars display a puzzling behaviour called nulling, where their radio emission abruptly becomes undetectable, or drops far below its normal level, for periods ranging from a handful of pulse periods (fractions of a second) to many hours or even days, before switching back on. The fraction of time a pulsar spends in this silent state — known as its nulling fraction — varies widely across the known population of normal pulsars, from nearly zero up to 95 per cent.

Until this study, nearly all measurements of nulling fractions had been obtained from single observations of each pulsar, leaving open the question of whether these fractions remain constant over years or decades. Researchers addressed this gap by tracking eight pulsars identified in the Parkes Multibeam Pulsar Survey over a span of eight to ten years. The team also applied a new method based on Bayesian statistics — a mathematical framework that updates probability estimates as new data arrive — to estimate each pulsar's nulling fraction from every individual observation session. This approach produced more rigorous, per-observation posterior estimates than prior techniques. In several of the eight pulsars examined, the nulling was found to suppress only specific sub-components of the pulse profile, rather than extinguishing all emission simultaneously.

The results show that most of the eight pulsars display no statistically significant change in their nulling fraction across the full observational baseline. However, three pulsars — PSR J1048-3832, PSR J1745-3040, and PSR J1825-0935 — show clear, statistically significant trends over the span of the data, meaning their nulling fractions have measurably shifted over the years of monitoring. This demonstrates that pulsar nulling is not necessarily a fixed property of a given pulsar and can evolve on timescales of years to decades. Because nulling is widely believed to reflect changes occurring in the pulsar magnetosphere — the complex high-energy region of charged particles surrounding the neutron star — tracking such long-term evolution can offer fresh insight into the physical processes driving pulsar emission and into the broader life cycle of pulsars as they age.

Scientific study

The Evolution of Nulling in Pulsars (external link)