We Heard You

Chapter One: Bindarra Downs

The desert made its own kind of quiet, and Zhu Peilan had learned to hear through it.

At Bindarra Downs the nearest town was two hundred and forty kilometres of corrugated red track away, and the nearest mobile phone tower might as well have been on another planet. That was the point. Radio astronomy needed silence the way a darkroom needed dark. Inside the radio-quiet zone there were no mobile phones, no wireless earbuds, no drones, no microwave ovens. The station's kitchen heated its food on a gas ring, and once a year a technician drove out with a spectrum analyser to hunt down the faint electric buzz of a failing fluorescent ballast, as though it were a wasp in a nursery.

Peilan liked all of it. She liked the shielded control room with its double door, the smell of dust and warm electronics, the way the forty-eight dishes of the Southern Transient Array stood out on the plain like a congregation with their heads tilted back. She liked the night shift most of all, because on the night shift nobody talked to her.

It was the third of March, a little after one in the morning, and she was three hours into an eight-hour watch when the line appeared.

She had been running the standard transient pipeline: an automated search for fast radio bursts, magnetar flares, the twitches and hiccups of a violent universe. The pipeline threw up candidates the way a beach throws up shells, and most of them were rubbish. Peilan's job was to look at the rubbish and say so.

The candidate on her screen was at 1427.0 megahertz. Narrow. Absurdly narrow — a spike less than a hertz wide, the kind of thing nature almost never made and human electronics made constantly.

"Interference," she said aloud, because talking to herself was one of the few luxuries the night shift allowed.

She pulled up the waterfall plot: frequency on one axis, time on the other, power in colour. The spike drew a straight bright thread down the screen, then stopped. Then, after a gap, started again.

She leaned in.

Burst. Silence. Burst. Silence.

Peilan had spent eighteen years staring at plots like this and she had a physical reaction to certain shapes, the way a carpenter's hands know a warped board. This shape made the skin on her forearms tighten.

She measured the bursts. Eleven point three seconds, each of them, to the limit of her time resolution. She measured the silences. Forty-seven point seven seconds. She measured nine cycles in a row and the numbers did not drift by so much as a millisecond.

Nothing in the sky did that. Pulsars were metronomes, yes, but pulsars were broadband and their pulses lasted milliseconds, not eleven seconds. A pulsar was a lighthouse. This was something holding a note, letting it go, holding it again, with a patience that made her feel watched.

"Satellite," she said. "It's a satellite."

She wanted it to be a satellite. She needed it to be a satellite, and she knew exactly why, and the knowing sat in her chest like a swallowed stone.

Three years ago Peilan had published a paper on a brown dwarf pair fourteen light-years away, LP 442-9, in which she claimed to have found an anomalous periodicity in the radio emission — a repeating structure with no astrophysical explanation. For six weeks she had been briefly, dizzyingly famous inside her field. Then a group in Toronto reproduced her analysis and demonstrated that the periodicity came from a temperature-dependent oscillation in the receiver's own frequency reference. Her signal had been the observatory breathing. She had discovered her own instrument.

She had done everything correctly afterwards. Retracted, apologised, written the humiliating erratum in the plainest language she could manage. It made no difference. Grant panels remembered. Her name acquired an invisible asterisk. Two years of applications went nowhere, and eventually she took what she could get: night operator, Bindarra Downs, a job for a postdoc, at forty-one years old.

So she did not get excited. She got methodical.

She opened the satellite catalogue and stepped through every object above the horizon in that patch of sky. Nothing at 1427 megahertz, which was inside a protected radio astronomy band, though protection was a legal concept rather than a physical one. She checked aircraft transponder logs; the nearest flight was a freight run at forty thousand feet, four hundred kilometres north, and its Doppler signature would have smeared across the band. She checked the station's own housekeeping telemetry: generator load steady, cryogenics nominal, no maintenance work logged. She checked the kitchen camera, because two decades earlier a famous observatory had chased mysterious signals for seventeen years before discovering that staff were opening the microwave door before the timer finished. The kitchen was dark and the microwave had been removed from the site in 2019.

Then she looked at the direction.

The array had been staring at a wide field in the southern sky, and when she narrowed down the position of the narrowband source she got a small ellipse of uncertainty in the constellation Grus — the Crane. Low and clean, well away from the galactic plane. Not the sort of place anybody's hardware pointed.

Peilan sat back in the chair and listened to the air conditioning.

In the desk drawer she kept her mother's wristwatch, a thin gold thing with a cracked crystal that ran about four minutes slow per day. She took it out sometimes, on long nights, the way other people checked their phones. She took it out now, turned it over, and put it back without winding it.

"All right," she said. "Let's be sure."

She did the one test no interference could survive. She commanded twelve of the dishes off-target, sixty degrees away, and watched the line vanish. She held them there for eleven minutes. Then she slewed them back.

The signal was waiting.

Not approximately waiting. She checked the phase of the cycle against the atomic clock in the timing hut and found that the bursts had continued exactly on schedule while she was looking elsewhere — that the pattern had not paused for her, had not noticed her, had been going on for however long it had been going on, indifferent as a tide.

At 3:40 a.m. she wrote in the log, in handwriting she barely recognised as her own:

Narrowband source, 1427.000 MHz. Duty cycle 11.3 s on / 47.7 s off. Position consistent, direction Grus. Off-source null confirmed. Cause unknown.

She underlined the last two words, then crossed the underline out, because underlining was a claim, and she had learned what claims cost.

Then she made a pot of tea, sat in the dark control room with the cup going cold in her hands, and listened to a stranger keeping perfect time.