Astronomers at the SETI Institute have made significant advancements in understanding how interstellar space affects radio signals from pulsars, which may enhance efforts to search for extraterrestrial life. Their research reveals that the gas between stars can cause minute delays—up to billionths of a second—in the arrival time of pulsar signals, crucial for using these cosmic clocks effectively.
The study, led by Grayce Brown, emphasizes that while these delays may be undetectable to the human eye, they are vital for experiments reliant on pulsars, particularly in the detection of low-frequency gravitational waves and the search for intelligent life beyond Earth. “Pulsars are wonderful tools that can teach us much about the universe and our own stellar neighborhood,” Brown stated. “Results like these help not just pulsar science, but other fields of astronomy as well, including SETI.”
Research Methodology and Findings
Starting in late February 2023, Brown and her team conducted a nearly daily observational campaign over a span of ten months, utilizing the Allen Telescope Array in California. Their focus was on the pulsar PSR J0332+5434, a rapidly spinning remnant of a neutron star located more than 3,000 light-years away, which is the brightest pulsar observable from the telescope.
Through nearly 400 observations, the researchers identified variations in the pulsar’s scintillation pattern—essentially the “twinkling” effect caused by interstellar gas—over periods extending to hundreds of days. As radio waves emitted from the pulsar’s poles traverse space, they interact with clouds of charged gas, primarily composed of free electrons. This interaction alters the signal, creating scintillation similar to how stars twinkle when viewed from Earth.
The movement of Earth, the pulsar, and the intervening gas leads to the formation of bright and dim patches across radio frequencies. As these patches evolve, they subtly affect the arrival time of the pulses, introducing timing discrepancies of tens of nanoseconds that can significantly impact astronomical observations.
Implications for Future Research
The minute differences between predicted and observed pulsar pulse arrival times can have substantial repercussions. Pulsar timing arrays aim to detect low-frequency gravitational waves by identifying correlated deviations in pulse arrival times, which may be caused by the stretching and squeezing of spacetime. If the effects of interstellar gas are not accurately accounted for, they can obscure or even mimic the faint signals that researchers seek to detect.
Beyond enhancing pulsar timing accuracy, the findings also offer valuable insights for SETI scientists. The ability to differentiate between genuine cosmic signals and interference from human-made sources could be crucial in the ongoing search for extraterrestrial intelligence. Brown explained, “Noticeable scintillation can help SETI scientists distinguish between human-made radio signals and signals from other star systems.”
The research informs scientists about the expected scintillation from a radio signal traversing the region around the pulsar. “If we don’t see that scintillation,” Brown noted, “then the signal is probably just interference from Earth.”
The observational campaign was part of a larger effort that monitored approximately 20 pulsars over the course of a year, following a pilot phase initiated in late 2022. Although the team did not identify a repeating pattern in scintillation changes, they suggest that future campaigns extending beyond a year could refine predictions and enhance corrections for interstellar distortion.
The findings of this study were published on December 10, 2025, in The Astrophysical Journal. As astronomers continue to refine their understanding of pulsar signals, the potential for discovering signs of life beyond Earth remains an exciting frontier in cosmic exploration.
