Earlier in 2026, a University of Sydney PhD student traced a 1.34497-hour radio pulse to a dead star. Today, its 1.368-hour orbit explains why the bursts repeat

Earlier in 2026, a University of Sydney PhD student traced a 1.34497-hour radio pulse to a dead star. Today, its 1.368-hour orbit explains why the bursts repeat. The source is ASKAP J1745−5051, a binary system in the Milky Way containing a white dwarf and a low-mass companion. Radio observations found bursts that returned about every 1.4 hours. Optical observations then measured the movement of gas in the system and found an orbital period of 1.368 ± 0.053 hours. X-ray observations showed another cycle of about 1.32 hours. Together, these measurements connect the radio bursts with the binary orbit.

How ASKAP J1745−5051 was found?

ASKAP J1745−5051 was found during the Rapid ASKAP Continuum Survey. The survey was conducted with CSIRO’s Australian SKA Pathfinder in Western Australia. The survey contained about three million radio sources. Only about 100 sources showed more than 10 per cent circular polarisation. ASKAP J1745−5051 was the only source among those 100 that did not have a known astronomical identification within 10 arcseconds.


The MeerKAT radio telescope later improved the position of the source. This allowed astronomers to match it with an optical source recorded by Gaia. Radio observations with ASKAP and the Australia Telescope Compact Array showed that the bursts returned every 1.34497 hours.

The bursts did not always behave in the same way. The source could stop producing detectable radio emission for several hours. Individual pulses also changed in shape, polarisation and frequency structure.

The discovery paper was published in Nature Astronomy on June 1, 2026. It described the radio bursts as elliptically polarised, narrowband and variable in frequency. Their brightness temperature was too high for normal thermal radiation. This means the radiation requires a coherent emission process involving ordered magnetic fields.

The orbit provides the missing link

Optical observations helped determine what was producing the radio signal. Spectra from the SOAR telescope and Magellan Observatory showed hydrogen and helium emission lines. The wavelengths of these lines shifted as emitting material moved toward and away from Earth. This movement allowed astronomers to calculate the radial velocity of the material and measure the binary orbit without relying only on the radio signal.

The measured spectroscopic orbital period was 1.368 ± 0.053 hours. The radio period was 1.34497 hours. The two measurements are consistent within the uncertainty. When rounded to one decimal place, both periods are about 1.4 hours. This agreement is central to the discovery. It indicates that the binary orbit is connected to the timing of the radio bursts.

The University of Sydney PhD student and lead author Kovi Rose described the system as a stellar Rosetta Stone. The comparison refers to the way the system can be studied through radio timing, optical movement and X-ray activity. It provides a reference for comparing other long-period radio transients.

What the white dwarf is doing?

The optical spectrum shows that ASKAP J1745−5051 is an accreting white dwarf binary. A white dwarf is the dense remnant left after a Sun-like star reaches the end of its normal stellar evolution. In this system, the white dwarf takes material from a low-mass companion.

The system belongs to the class known as magnetic cataclysmic variables. The word cataclysmic is a historical term for this type of binary. It does not mean that the system explodes during every orbit.

Material from the companion crosses the region controlled by the white dwarf's gravity and moves toward the white dwarf. The magnetic field can direct this material along magnetic field lines instead of allowing all of it to form a complete accretion disc.

The original study found that ASKAP J1745−5051 is consistent with a polar or slightly asynchronous polar. These are two types of magnetic cataclysmic variables. However, the white dwarf's spin was not measured well enough to determine which type applies.

As the gas falls toward the white dwarf, it can heat and produce ultraviolet and X-ray radiation. The observations therefore provide evidence that material is actively moving from the companion toward the white dwarf.

X-rays show another part of the same cycle

X-rays provide a third way to measure the system. Swift and Einstein Probe detected variable X-ray emission. The X-ray period was measured at 1.32 ± 0.13 hours. This agrees within its uncertainty with both the optical orbital period and the radio period.

The X-ray brightness also changed by more than an order of magnitude between observations. This supports the idea that the rate or pattern of accretion changes over time. However, the radio and X-ray signals did not always reach their peaks at the same orbital phase.

ASKAP and ATCA detected radio pulses at phases that differed from the Einstein Probe X-ray maximum. MeerKAT later detected radio emission closer to the X-ray phase. This difference suggests that the radio and X-ray signals may come from different regions. Hot gas moving toward the white dwarf can produce X-rays, while the radio bursts require a coherent process connected with the magnetic field.

Why the radio bursts are so unusual?

The radio bursts can approach 100 per cent polarisation. Their minimum brightness temperature is above one trillion kelvin. At this level, electrons cannot simply produce the radiation independently through an incoherent process. The emission must be organised so that the waves reinforce one another.

The research team proposed relativistic electron cyclotron maser emission as a possible mechanism. Under this process, energetic electrons moving through a strong magnetic field can generate coherent and highly polarised radio emission.

The radiation would also be directed into a beam. Earth would detect the beam when the magnetic geometry points it toward us. This can explain why radio bursts disappear for periods even though activity continues within the binary.

A model involving two interacting magnetic dipoles reproduced several features seen in the observations. These included double-peaked bursts, changes in upper and lower frequency cut-offs, changes in the gap between peaks and periods without detected radio emission.

The model shows that magnetic geometry can produce these patterns. It does not provide a direct map of the magnetic fields. Plasma flow, gravity and particle acceleration may also affect the radio signal.

What the frequency patterns may mean?

The radio spectrum also contains narrow modulation lanes that are about 10 megahertz wide. These patterns resemble features found in decametric radiation produced by Jupiter during its interaction with Io. The comparison does not mean that the white dwarf binary works in the same way as the Jupiter-Io system.

Instead, the similarity suggests that plasma close to ASKAP J1745−5051 may affect the radio beam before it reaches Earth. The plasma could act as an interference screen and create some of the observed frequency patterns.

What this means for long-period radio transients?

Long-period radio transients are radio sources that repeat over periods ranging from minutes to hours. This is much slower than the timing of ordinary radio pulsars. Because of their slow periods, some explanations have involved neutron stars or magnetars rotating at very low speeds.

There is a problem with this explanation. Standard pulsar models indicate that an isolated neutron star eventually reaches a point where its rotation is too slow to maintain strong coherent radio emission. White dwarf binaries provide other possible clocks.

The repeating period could be linked to the binary orbit, the white dwarf's spin, or a beat between two periods that are close to each other. Magnetic interaction between the two stars can also supply charged particles and changes in magnetic geometry without requiring an isolated object to rotate once every hour.

Other sources show why the population may not have one explanation. GLEAM-X J0704−37, for example, has been associated with an M dwarf and a possible white dwarf and produces a radio transient over about three hours.

ASKAP J1745−5051 provides more evidence because its optical spectrum shows gas transfer and its X-rays show activity linked with accretion. However, the discovery does not prove that all long-period radio transients are cataclysmic variables.

Some sources have no optical binary counterpart. Others show different polarisation, pulse duration or high-energy behaviour. The wider population may contain accreting white dwarf binaries, non-accreting white dwarf binaries, neutron stars and other systems.

The companion star is still under study

The identity and properties of the companion are not fully settled. The discovery team estimated that the companion may be a late M-type star with a mass of about one-tenth that of the Sun. However, another star located only 0.9 arcseconds away affects some of the optical measurements. Gaia's parallax measurement was also not precise enough to establish the distance with confidence.

A later preprint used observations covering ultraviolet to infrared wavelengths. After removing measurements affected by blending and fitting model atmospheres, its authors favoured a white dwarf with a temperature near 15,000 kelvin. The same work suggested a donor with a temperature near 1,800 kelvin and a mass of about 0.05 solar masses. It estimated the distance at around 320 parsecs.

That study has been submitted for publication but has not been peer reviewed. Its near-infrared measurements also require separation of two nearby sources. The results should therefore be treated as evidence rather than a final description of the system.

If those measurements are supported, the companion would be closer to a brown dwarf than a red dwarf. The binary could also be a period bouncer, meaning a system that has evolved beyond the minimum orbital period expected for ordinary cataclysmic variables.

Why astronomers call it a Rosetta Stone?

The term Rosetta Stone is useful here because the same system can be read through different forms of observation. Radio telescopes measure the repeating bursts. Optical spectroscopy measures the movement of material and establishes the orbit. X-ray telescopes measure activity linked with accretion. Each form of observation provides information that the others cannot provide alone.

Astronomers can now compare these features with other long-period radio transients. If another source has matching radio and orbital periods, accretion lines, X-ray changes, high polarisation and similar frequency patterns, it could point toward a related white dwarf system. If those features are absent, other explanations may remain more suitable, including neutron stars or non-accreting white dwarf binaries.

What remains unknown?

Several questions remain open. The white dwarf's spin has not been measured separately. The distance also needs a better measurement. The proposed radio emission mechanism remains a model rather than something directly observed.

The companion's mass also needs better measurements through cleaner imaging and spectroscopy. Future observations can test whether changes in radio and X-ray activity are connected through changes in the magnetic interaction between the two stars.

ASKAP J1745−5051 therefore does not explain every long-period radio transient. It provides a system where several measurements point toward the same binary clock. About every 1.4 hours, the two stars move through a changing magnetic geometry. Gas moving toward the white dwarf produces X-rays, while a radio beam can sweep toward Earth and produce the detected bursts.

The 1.34497-hour radio pulse and the 1.368-hour orbital period are therefore more than two separate measurements. Their agreement gives astronomers a way to connect the repeating radio signal with the binary system and provides a reference point for studying other long-period radio transients.