- A radio object pulses every 22 minutes, defying known stellar physics.
- The signal has repeated steadily since 1988, unnoticed for decades.
- A 2026 study suggests it may be a binary white dwarf system.
Natasha Hurley-Walker was scanning the Milky Way with a radio telescope in outback Western Australia when she found something she couldn't explain. A signal, arriving every 22 minutes with machine-like regularity. Not the frantic tick of a pulsar. Something far slower, far steadier, and far more puzzling. It was a long-period radio transient unlike anything astronomers had seen before.
The object, now catalogued as GPM J1839-10, lies some 15,000 light-years away in the constellation Scutum. When Hurley-Walker's team at the International Centre for Radio Astronomy Research (ICRAR) at Curtin University began searching archival data, the mystery deepened considerably. The signal had been there since at least 1988.
Buried in decades of telescope records. Unnoticed. Waiting.
How slow is slow?
1,000x
GPM J1839-10 rotates roughly 1,000 times slower than a typical pulsar, well past the threshold where radio emission is supposed to stop.
Dead Stars Don't Usually Send Long-Period Radio Signals
Pulsars are neutron stars: the collapsed cores left behind when massive stars die. They are extraordinarily dense objects, some packed with more mass than our Sun into a sphere no wider than Manhattan.
As they spin, their magnetic poles sweep radio waves across the sky like a lighthouse beam.
Over time, pulsars slow down. As rotation slows, the magnetic field weakens. Eventually, a pulsar crosses what astronomers call the "death line", a threshold below which pair production in the magnetosphere can no longer sustain radio emission.
Past this line, the lighthouse goes dark.
What is the death line?
The death line marks the theoretical limit beyond which a neutron star can no longer generate the particle cascades needed to produce radio waves. It depends on both rotation speed and magnetic field strength. Once a neutron star rotates slowly enough, or its field weakens enough, radio emission is expected to stop. GPM J1839-10 sits well past even the most generous estimate of this limit. Yet it keeps transmitting.
GPM J1839-10 rotates once every 21 minutes and 58 seconds. Typical radio pulsars complete a rotation in one to ten seconds. At that pace, the object should have crossed its death line long ago.
And yet every 22 minutes, it emits bursts of polarised radio energy lasting up to five minutes.
Hiding in Plain Sight Since 1988
The signal had been sitting in telescope archives for decades before anyone thought to look. When the team searched records at the Very Large Array in New Mexico and the Giant Metrewave Radio Telescope in India, they found the same pulse stretching back to 1988, recorded again and again, unexamined, because nobody had expected anything so slow.
"I was five years old when our telescopes first recorded pulses from this object," Hurley-Walker noted, "but no one noticed it, and it stayed hidden in the data for 33 years. They missed it because they hadn't expected to find anything like it."
Every 22 minutes, it emits a five-minute pulse of radio wavelength energy, and it's been doing that for at least 33 years. Whatever mechanism is behind this is extraordinary.
Dr. Natasha Hurley-Walker, ICRAR, Curtin University
That stability is itself a problem. Over 35 years, the rotation period has changed by no more than 0.28 milliseconds, a near-perfect clockwork. If the object were a magnetar powering its emission through the energy of its slowing rotation, the spin-down rate would need to be fast enough to explain the radio output.
It isn't.
The energy budget simply doesn't work. Magnetar starquakes were considered as an alternative mechanism; they release enormous bursts of energy, but starquakes are temporary phenomena. Sustaining radio emission for over three decades from that mechanism alone is incompatible with what is known about magnetar physics.
A New Class of Object, or an Old Star in Disguise?
The original 2023 paper raised two alternatives to the magnetar model. A highly magnetised white dwarf was one candidate, less dense than a neutron star and rotating slowly enough to fit the observed period.
The difficulty is that no known lone white dwarf produces radio emission anywhere near this luminous.
More On Signals From Space
Gravitational Wave Hunters Find Hidden Signals on a Desktop
While physicists waited decades for space missions, tabletop detectors cracked open a frequency band that was supposed to be unreachable from Earth.
→The picture shifted in early 2026, when a study published in Nature Astronomy proposed a more specific scenario. From 36 years of radio timing data, the team inferred that GPM J1839-10 may be a white dwarf in a binary system with a small companion star, likely an M-dwarf. In this model, the 22-minute pulsing arises not from the white dwarf's rotation but from its magnetic axis periodically sweeping through the companion's stellar wind.
No optical counterpart has yet been confirmed. No X-rays have been detected.
The binary hypothesis remains a proposal, not a settled answer.
The Search Has Only Just Begun
What is settled is that GPM J1839-10 belongs to a category that did not exist in the literature before 2022: long-period radio transients, objects that pulse on timescales of minutes rather than seconds. Hurley-Walker's team expects more of them are already hiding in archival data, waiting for someone to search at the right timescale.
The Square Kilometre Array, currently under construction across Australia and South Africa, will survey the sky with far greater sensitivity.
If similar objects are out there, the SKA should find them. Whatever their nature, whether extreme magnetars, magnetic white dwarfs in binary systems, or something not yet imagined, they will require revising what we thought we understood about the conditions under which dead stars go quiet.
More mysterious signals are likely to be waiting for us.
Sources
- Primary Research: A long-period radio transient active for three decades (Nature, July 2023, Hurley-Walker et al.)
- Additional Context:
- Hiding in plain sight, astronomers find new type of stellar object (ICRAR press release)
- Another Object Has Been Found Emitting Strange Radio Signals in Our Galaxy (ScienceAlert)
- Constraints on an optical counterpart for GPM J1839-10 (arXiv, September 2025)
Fact Check: Claim-by-Claim Verification Verified
The article accurately describes GPM J1839-10, long-period radio transients, and current leading models, with appropriate caveats about what is still uncertain.
Commentary
- The newer white-dwarf–binary interpretation, presented as a 2026 Nature Astronomy study, is strongly supported by recent work but is still relatively fresh and not yet universally accepted; describing it as a leading “proposal” rather than a settled fact is appropriate, and the article generally maintains that distinction.
Sources used for verification
Academic/Peer-reviewed:
- A long-period radio transient active for three decades - nature.com
- A highly magnetized long-period radio transient exhibiting unusual emission features - science.org
- A binary model of long period radio transients: GPM J1839-10 as a white dwarf–M-dwarf system - arxiv.org
- Constraints on an optical counterpart for the long-period radio transient GPM J1839-10 - arxiv.org
- Constraints on an optical counterpart for the long-period radio transient GPM J1839-10 - academic.oup.com
Other reliable sources:
- Hiding in plain sight, astronomers find new type of stellar object - icrar.org
- Binary dance: a white dwarf system explains mysterious radio pulses - icrar.org
- Puzzling slow radio pulses are coming from space. A new study might explain them - phys.org
- A long-period radio transient active for over three decades - atnf.csiro.au
Fact-checked by Perplexity Sonar Pro on 2026-03-07
