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Cosmic radio pulses that repeat every few minutes or hours, called long-period transients, have been puzzling astronomer Since their Discover 2022. Our new research, published today in Nature Astronomy , may finally add some clarity.
Radio astronomers are familiar with pulsars, a type of type fast spinning neutron star. To us observing the sky from Earth, these objects appear pulse Because powerful beams of radio waves from the poles are sweeping over us telescope – much like a cosmic beacon.
The slowest pulsars rotate in just a few seconds – this is called the pulsar’s period. But in recent years, long-period transients have also been discovered. These times range from 18 minutes to over 6 hours.
From everything we know neutron starthey should not be able to generate radio waves as they spin slowly. So, what’s wrong with physics?
Well, neutron stars aren’t the only dense stellar remnants on this block, so maybe they’re not the star of this story after all. Our new paper provides evidence that the longest-lived long-period transient, GPM J1839-10, is actually white dwarf Star. It produces powerful radio beams with the help of a stellar companion, meaning other stars may be doing the same thing.
Enter the white dwarf pulsar
Like neutron stars, white dwarfs are the remnants of dead stars. They are about the same size as the Earth, but their mass is equal to the total mass of the Sun.
Isolated white dwarfs have not been observed emitting radio pulses. But when they are paired with an M dwarf (an ordinary star with about half the mass of the Sun) in a tight binary star system called a binary star, they have the necessary ingredients to do so.
In fact, we know that such rapidly rotating “white dwarf pulsars” exist because we have observed them – the first one was confirmed in 2016.
This raises the question: could long-period transients be the slower cousins of white dwarf pulsars?
More than a dozen long-period transients have been discovered so far, but they are so far away and so embedded in our galaxy that it is difficult to tell what they are. It was not until 2025 that the two long-period transients were finally identified as white dwarf-M-dwarf binaries. This is very unexpected.
However, it leaves astronomers with more questions.
Even if some long-period transients are white dwarf-M dwarf binaries, do they radiate in the same way as faster white dwarf pulsars? Are long-period transients visible only at radio wavelengths destined to remain a mystery forever?
What we need is a model that works for both, and a long-period transient model with enough high-quality data to test it.
A unique example of longevity
In 2023, we discovered GPM J1839-10, a long-period transient with a period of 21 minutes. It was only the second such discovery ever, but unlike its predecessors or those since, it was remarkably long-lived. Pulses were discovered in archival data as early as 1988, but were only detected a few times when they should have been.
Since it is 15,000 light-years away, we can only see it via radio waves. So we took a closer look at this seemingly random, intermittent signal to learn more.
We looked at GPM J1839-10 in a series called Around the World observations. These projects use three telescopes, each passing light to the next as the Earth rotates: Australia’s SKA Pathfinder, or ASKAP, South Africa’s MeerKAT radio telescope, and the United States’ Karl G. Jansky Very Large Array.
It turns out that the intermittent signals are not random at all. The pulses arrive in groups of four or five, with each group occurring in pairs two hours apart. The entire pattern repeats every nine hours.
This stable pattern strongly suggests that the signal comes from a binary system of two celestial bodies orbiting each other every nine hours. Knowing this period also helps us calculate their masses, which all add up to a white dwarf-M-dwarf binary.
Checking back, not only did the archival detections agree with the same pattern, but we were able to use the combined data to refine the orbital period to an accuracy of just 0.2 seconds.
heartbeat pattern
The radio data alone tells us that GPM J1839-10 is definitely a binary system. What’s more, there are also strange ones heartbeat Its pulses provide clues to its nature in a way that is only possible by observing radio signals.
Inspired by previous studies of white dwarf pulsars, we modeled GPM J1839-10 as a white dwarf that produces radio beams as its magnetic poles sweep through the stellar wind of its companion star. Different alignments of binaries with our line of sight throughout their orbit can accurately predict heartbeat patterns.
About the author
Csanád Horváth is a PhD student in Radio Astronomy at Curtin University. Natasha Hurley-Walker is a radio astronomer at Curtin University. This article is reproduced from dialogue Licensed under Creative Commons. read Original article.
We can even reconstruct the geometry of the system, such as the distance between the stars and their masses.
All in all, GPM J1839-10 has the potential to be the missing link between long-period transients and white dwarf pulsars.
With the help of our model, other astronomers have been able to detect changes in the period of our measured optical data with high precision, albeit without being able to distinguish between binary pairs.
Research into how emission physics works and how the broader long-period transient properties fit together is ongoing. However, this is a critical step in understanding.