Astronomers searching for alien life are sharpening our cosmic clocks. Here’s why

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Astronomers at the SETI (Search for Extraterrestrial Intelligence) Institute have learned to read the subtle “flicker” of a distant cosmic beacon, revealing how interstellar space distorts radio signals as they pass through the galaxy.

Research shows that gas between stars can shift the arrival time of a pulsar’s signal by just a few billionths of a second.

Although imperceptible to humans, these tiny delays are important for experiments that rely on pulsars as ultra-precise cosmic clocks, the researchers say, particularly for efforts to detect low frequencies. gravitational waves and search for signs of intelligent life beyond Earth.

“Pulsars are wonderful tools that can teach us a lot about the universe and our own stellar neighborhood,” said study lead author Grayce Brown of the SETI Institute. statement. “Results like these not only help pulsar science, but also other areas of astronomy, including SETI.”

Starting in late February 2023, Brown and his team conducted an almost daily observation campaign lasting 10 months using the system operated by SETI. Allen Telescope Array in California. The team tracked subtle changes in radio signals from the PSR J0332+5434 pulsar, the rapidly rotating remnant of a neutron star located more than 3,000 light-years from Earth and the brightest. pulsar visible through a telescope.

From nearly 400 observations, the team identified changes in the pulsar’s “flicker” pattern, known as scintillation, on timescales of several hundred days. As radio waves emitted from the pulsar’s poles travel through space, they pass through clouds of charged gas, mostly free electrons, which bend, scatter, and slightly delay the signal. This interaction produces scintillation, the radio equivalent of the way stars appear to twinkle in Earth’s atmosphere, according to the study.

As the Earth, pulsar, and interstellar gas move relative to each other, bright and dark spots form on radio frequencies and change over time. These lag patterns subtly change as the pulses arrive, introducing delays on the order of tens of nanoseconds, the release said.

Such tiny differences between the predicted and observed arrival times of the pulsar pulses can have disproportionate consequences. Pulsar timing arrays search for low-frequency gravitational waves by looking for correlated gaps in pulse arrival times caused by the stretching and compression of space-time. If the delays introduced by interstellar gas are not properly accounted for, they can obscure – or even mimic – the faint signals that researchers are trying to detect, the study notes.

In addition to helping improve the timing of pulsars, scientists say the results also provide a valuable tool for SETI researchers working to distinguish genuine cosmic signals from human-caused interference. “Visible scintillation can help SETI scientists distinguish between human-emitted radio signals and signals from other star systems,” the release said.

“We need a way to differentiate signals coming from Earth from those coming from beyond our solar system,” Brown said. The debriefing. “Thanks to this research, we know how much scintillation to expect from a radio signal passing through the interstellar space region of this pulsar.”

“If we don’t see this scintillation,” she added, “then the signal is probably just interference from Earth.”

The observations were part of a larger effort that monitored about 20 pulsars for about a year, following a pilot phase in late 2022. Although the team did not identify a repeating pattern in scintillation changes, the study notes that future observational campaigns lasting longer than a year could further refine predictions and improve corrections for interstellar distortion.

The study was published on December 10, 2025 in The Astrophysical Journal.