Since 2022, strange radio signals from the Milky Way have baffled astronomers. They arrived from the galactic plane with a seemingly impossible cadence; They were too slow to be pulsars and too regular to be just noise. They called them long-period radio transients (LPTs), and for years no one knew what they were.

Now, a study published in Nature Astronomy and led by an international team of astronomers from the University of Sydney has made a finding that could change that situation.

Astrophysicist Kovi Rose and his colleagues managed to trace one of these mysterious pulses to its source and have found something that no one expected, or perhaps they did, but never with such clarity.

A binary system at the heart of the mystery

The object in question is called ASKAP J1745−5051. It is a binary system formed by a white dwarf – a dead stellar core about the size of the Earth, but with a mass close to that of the Sun – and a red dwarf of just one tenth of that mass.

The two orbit around each other at such a short distance that they complete a full revolution in just over 81 minutes, according to Science Alert.

At this extreme proximity, the white dwarf's gravity tears material from its companion and drags it toward itself. The result is periodic bursts of radio waves and X-rays that repeat with each orbit, like a cosmic beacon with extraordinary regularity.

The “Rosetta Stone” of cosmic signals

One of the reasons why this system is so interesting is that it combines characteristics that until now have been observed separately in different transients.

According to Science Alert, it combines a white dwarf, a binary companion, intense magnetic activity, radio emission, X-ray emission and matter transfer between stars. No other known LPT had brought together all of these characteristics so clearly and simultaneously.

Therefore, researchers describe it as a possible “Rosetta stone” for these phenomena. The reference to the famous archaeological find is not coincidental: just as the Rosetta Stone made it possible to decipher Egyptian hieroglyphs by presenting the same text in different scripts, this system, which brings together in a single object several of the clues previously observed separately, could help interpret other similar signs.

And the discovery is not minor. As Rose himself explains in an article for The Conversation, until now only a dozen of these transients had been detected in different corners of the galaxy, but the origin of most remained a mystery.

The most popular hypothesis attributed them to pulsars – rotating neutron stars – but it presented a problem: physical models indicate that a neutron star that rotates so slowly should not be able to emit radio signals, so the explanation did not add up.

In this context, the new discovery reinforces an alternative theory, according to which at least some of these transients come from binary systems with white dwarfs in the process of accretion, what astronomers call cataclysmic variables.

X-rays, radio and magnetic fields: the mechanism in two acts

In the case of ASKAP J1745−5051, the evidence obtained for this system is especially strong. Optical observations from the SOAR telescope confirmed the binary nature of the system. NASA's Swift observatory and the Einstein Probe detected the X-rays. And the Australian CSIRO's ASKAP radio telescope recorded the radio flashes with great precision.

Taken together, the observations allow us to reconstruct a possible mechanism in two acts.

First, the material torn from the red dwarf falls on the surface of the white dwarf, heats up to millions of degrees and emits X-rays.

Second, the interaction between the powerful magnetic fields of both stars – thousands of times more intense than those of an MRI machine, as Rose describes – would accelerate charged particles responsible for the radio pulses.

Interestingly, as indicated in a statement from the University of Sydney, the two signals do not reach their maximum at the same time, suggesting that they originate from different regions of the system.

Despite detailed measurements, the object's exact distance remains uncertain. According to Science Alert, estimates place it between 1,300 and 30,000 light years from Earth, an extraordinarily wide range that highlights the difficulties that still exist in accurately determining the distance to this type of system.

Open questions about long period transients

Even so, this uncertainty does not overshadow the value of the discovery. “Some similar objects have been linked to binary systems before,” says astrophysicist Tara Murphy of the University of Sydney, “but this is the first one where we can clearly see both the stars and the accretion process in action,” she adds.

For now, the team, which brought together scientists from the United States, China, Canada, Spain, Israel and Australia, plans to continue observations by combining multiple types of telescopes. The question that remains open is whether all long-period transients share this same origin or whether some respond to different physics.

“Each new discovery helps us complete the bigger picture,” Rose says. “We are just beginning to understand this new class of cosmic phenomena.”