Three years ago, scientists recorded a mysterious repeating radio signal from outer space that couldn’t easily be explained.
Now, those same scientists believe they have found a potential source for such strange celestial broadcasts. Spoiler: it’s probably not aliens.
Back in 2021, during lockdown, Australian undergraduate astronomer Tyrone O’Doherty spotted an unusual burst of radio waves that repeated every 18 minutes.
Repeating radio signals aren’t that weird in the grand scheme of our universe, and usually emanate from rapidly-spinning collapsed stars known as pulsars.
But at the time, scientists had never seen a pulsar repeat as slowly as 18 minutes, and commonly accepted theories of how pulsars work suggested that shouldn’t be possible.
“At this point I broke out in a cold sweat,” wrote O’Doherty’s supervisor Natasha Hurley in January 2022.
“There is a worldwide research effort searching for repeating cosmic radio signals transmitted at a single frequency. It’s called the Search for Extra-Terrestrial Intelligence. Was this the moment we finally found that the truth is out there?”
In fact, as Hurley made clear at the time, the sheer power of the signal suggested it could only come from a natural source. Nevertheless, the exact nature of that source remained mysterious.
By scanning the sky with radio telescopes, Hurley and her team located another, similar radio pulse that repeated only once every 2.9 hours – the slowest ever observed so far.
Closer observation showed that the signal came from a red dwarf star, but also revealed some quirks suggesting that the radio signal was actually coming from another object locked in binary orbit with the dwarf itself.
“Based on previous studies of the evolution of stars, we think this invisible radio emitter is most likely to be a white dwarf, which is the final endpoint of small to medium-sized stars like our own Sun,” wrote Hurley.
The culprit in that case would probably be the red dwarf’s stellar wind – a continuous stream of charged gas that would sometimes strike the white dwarf as they danced around each other in mutual gravitation.
When that happened, the stellar wind would be accelerated by the other body’s magnetic field, producing radio waves.
“Maybe as we find more examples, we will work out a unifying physical model that explains all of them. On the other hand, there may be many different kinds of system that can produce long-period radio pulsations,” Hurley concluded.
