Story by Wiliam Hunter

Over the last 10 years, Earth has been receiving a mysterious radio signal every two hours from a distant region of space.

Although it sounds like the start of a sci-fi novel, scientists have now traced these pulses back to an ‘unprecedented’ source.

The researchers say that the pulses originate from a binary system containing a long-dead star.

In this system, a white dwarf and red dwarf orbit each other so closely that their magnetic fields ‘bump together’ to create a long radio pulse.

Since the stars’ orbit is regular, they produce a pulse every 125 minutes like a vast cosmic clock.

Researchers say this system, named ILTJ1101, is located 1,600 light-years from Earth in the direction of the Big Dipper, within the constellation Ursa Major.

This is the first time that a repeating long radio pulse has been observed coming from anything other than a highly magnetised neutron star, known as a magnetar.

In the future, the researchers believe that more mysterious signals from space might turn out to be binary systems like this one.

Researchers have traced the origins of a mysterious radio signal to an ‘unprecedented’ part of space. Their study claims that the burst has been produced by a binary system containing a red dwarf and white dwarf star (illustrated)

Dr Iris de Ruiter, now of the University of Sydney, first discovered the mysterious pulses in 2024 while looking through an archive of data from a radio telescope in the Netherlands.

Within the data of the Low Frequency Array (LOFAR), the largest radio telescope operating at the lowest frequencies that can be observed from Earth, Dr de Ruiter discovered a pulse arriving at Earth in 2015.

Sifting through the archival data for the same area of the sky, she soon found six more pulses.

What was unusual was that each pulse, like a flash of light from a torch but in radio form, lasted between a few seconds to a minute and arrived at regular intervals.

As radio-astronomy techniques have improved, scientists are spotting more and more ‘fast radio bursts’ (FRBs) but this kind of slow, regular pulse remain rare.

Study co-author Dr Charles Kilpatrick, of Northwestern University, says: ‘The radio pulses are very similar to FRBs, but they each have different lengths.

‘The pulses have much lower energies than FRBs and usually last for several seconds, as opposed to FRBs which last milliseconds.‘

To learn more about where these pulses were coming from, the researchers accessed a large optical telescope, which would gather light from that region of space.

While regular radio pulses have been theorised to be signs of intelligent life, the researchers say this pulse is produced by the magnetic fields of the two stars bumping together as they orbit (stock image)

Starting a decade ago, scientists detected a regular radio pulse arriving once every 125 minutes from a distant region of space. Until now, the origin of this pulse has been a mystery. This diagram shows how the orbital period of the binary system (blue) matches the radio pulses

At first, only one star was visible, but the data soon revealed more about this strange system.

By looking at the optical spectra of the star – the different frequencies of light that reach the telescope – the researchers learned that the one visible star was a red dwarf.

Red dwarfs are small, cool stars just a fraction the size of the sun, which can burn for trillions of years without using up all their fuel.

However, this particular red dwarf was doing something unusual: it was wobbling back around a central point on a regular schedule.

Dr Kilpatrick says: ‘The spectroscopic lines in these data allowed us to determine that the red dwarf is moving back and forth very rapidly with exactly the same two-hour period as the radio pulses.’

This back-and-forth movement suggests that the red dwarf was being pulled by the gravity of a second, hidden star.

By observing those movements carefully, Dr Kilpatrick calculated that this second star had the same mass as a typical ‘white dwarf’ star.

White dwarfs are dead stars which have burned through all their nuclear fuel and shed their outer layers, leaving behind nothing but their hot, dense core.

The system includes a white dwarf, a dead star so small and faint that they don’t usually show up on optical telescopes. The researchers were only able to determine the white dwarf existed because of its pull on its partner star. Pictured: Artist’s impression of a white dwarf next to our moon for scale

But, since these stars are so dim, they don’t show up on any but the most powerful telescopes – which explains why the researchers couldn’t directly observe it.

The researchers believe that, as the white and red dwarfs dance around a central point, their magnetic fields come close enough to interact and produce a blast of radio waves.

Around 1,600 years later, those radio waves arrive on Earth as the mysterious radio pulses which showed up in Dr de Ruiter’s database.

Dr Kilpatrick says: ‘In almost every scenario, its mass and the fact that it is too faint to see means it must be a white dwarf.

‘This confirms the leading hypothesis for the white dwarf binary origin and is the first direct evidence we have for the progenitor systems of long-period radio transients.’

Going forward, the researchers hope that their study will inspire other astronomers to consider binary systems as the possible source of unusual radio pulses.

This could help us understand many of the mysterious energy sources which have been found throughout the Milky Way.

Lead author Dr de Ruiter says: ‘With different techniques and observations, we got a little closer to the solution step by step.’

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