The universe is awash with strange radio signals, but astronomers have now detected a really bizarre one that repeats every hour, cycling through three different states. While they have some ideas about its origin it can’t be explained by our current understanding of physics.
The signal first appeared in data gathered by the ASKAP radio telescope in Australia, which watches a big swath of sky at once for transient pulses. Officially designated ASKAP J1935+2148, the signal seems to repeat every 53.8 minutes.
Whatever it is, the signal cycles through three different states. Sometimes it shoots out bright flashes that last between 10 and 50 seconds and have a linear polarization, meaning the radio waves all “point” in the same direction. Other times, its pulses are much weaker with a circular polarization, lasting just 370 milliseconds. And sometimes, the object misses its cue and stays silent.
“What is intriguing is how this object displays three distinct emission states, each with properties entirely dissimilar from the others,” said Dr. Manisha Caleb, lead author of the study. “The MeerKAT radio telescope in South Africa played a crucial role in distinguishing between these states. If the signals didn’t arise from the same point in the sky, we would not have believed it to be the same object producing these different signals.”
So what could be behind such a weird radio signal? Let’s get it out of the way up front: it’s not aliens (probably). The most likely explanation, according to the scientists who discovered it, is that it’s coming from a neutron star or a white dwarf. But it’s not a neat solution, since the signal’s weird properties don’t fit with our understanding of the physics of those two kinds of objects.
Neutron stars and white dwarfs are fairly similar, but with some key differences. They’re both born from the deaths of bigger stars, with the original mass dictating whether you end up with a neutron star or a white dwarf.
Neutron stars are known to blast radio waves out regularly, so they’re a prime suspect here. It’s possible that signals this varied could be produced by interactions between their strong magnetic fields and complex plasma flows. But there’s a major problem: they usually spin at speeds of seconds or fractions of a second per revolution. It should be physically impossible for one to spin as slow as once every 54 minutes. White dwarfs, on the other hand, would have no problem spinning that slowly, but as the team says, “we don’t know of any way one could produce the radio signals we are seeing here.”
This isn’t the first time a repeating radio signal from space has stumped scientists. Another was found a few years ago on an 18-minute loop, which should also be impossible. This new one is not only far longer but more complex, deepening the mystery.
Whether the signal is from an unusual neutron star, an elusive “white dwarf pulsar,” or something else entirely, can only be answered with more observations.
“It might even prompt us to reconsider our decades-old understanding of neutron stars or white dwarfs; how they emit radio waves and what their populations are like in our Milky Way galaxy,” said Caleb.
The research as published in the journal Nature Astronomy.
Sources: University of Sydney, The Conversation
