Mysterious Signal Coming From a Dead Star and Its Companion
Astronomers have tracked down the source of a mysterious radio signal from deep space repeating every two hours. Intriguingly, it's a pair of stars in such a tight orbit that their magnetic fields regularly bump into each other — and it's this bodily percussion that appears to be blasting out the radio emissions we're picking up on Earth, roughly 1,600 light years away.
The findings on the binary system, published in a new study in the journal Nature Astronomy, shine a much-needed light on a new class of cosmic signal known as long-period radio transients.
These extremely rare repeating radio pulses are similar to what's emitted by rapidly rotating stars called pulsars, whose signals we see every time their poles turn towards Earth, but repeat every few minutes — or even hours — compared to the latter's sub-second intervals.
Simply put, it would be impossible for pulsars to rotate slowly enough to produce long period transients, and astronomers have searched far and wide for alternative sources.
"Now, we know at least some long-period radio transients come from binaries," said study coauthor Charles Kilpatrick, an astrophysicist at Northwestern University, in a statement about the work. "We hope this motivates radio astronomers to localize new classes of sources that might arise from neutron star or magnetar binaries."
The radio pulses — seven of them — were first discovered last year using the Low Frequency Array radio telescope in Europe.
"Taking a closer look at the timing of these pulses, we found that they arrive every two hours," wrote lead author Iris de Ruiter at the University of Sydney in an essay for The Conversation. "We compared the location of the radio pulses to optical catalogues, which list stars and galaxies that telescopes have observed in visible light. And there it was – we found there was a faint red star exactly at the location of our radio pulses."
The faint star is a red dwarf — a small but extremely ubiquitous main sequence star. But it couldn't produce the signal on its own, de Ruiter wrote. There had to be a companion; binary systems, after all, are common.
To find the hidden partner, the astronomers looked at the spectra of light coming from the red dwarf. They found that the light would intermittently shift to shorter and longer wavelengths, a sign that the star is moving back and forth. And that could only mean that it's locked in orbit with another object.
That turned out to be a stellar remnant known as a white dwarf. White dwarfs are sometimes referred to as "dead stars" because they're the leftover, hot core of a massive star that exploded in a supernova.
Still, de Ruiter says we're just scratching the surface of long period transients, because not all of them will come from binary systems like this one.
"The current landscape of long period transients is sparse. We need to find more of them to get a full understanding of these mysterious objects and how they work," de Ruiter wrote in The Conversation. "However, we now know that white dwarfs, with a little help from a stellar friend, can produce radio pulses just as bright as neutron stars."
More on stars: Scientists Realize They Witnessed the Last Gasp of a Planet as It Met a Horrible Fate
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