Astronomers don’t know what’s causing these weird radio waves from a nearby star

Bizarre radio signals seem to be coming from a small red star about 11 light-years from Earth, and astronomers aren’t exactly sure what’s causing them.

The signals were first picked up in May by scientists at the Arecibo Observatory in Puerto Rico. The astronomers there were observing red dwarfs — small, cool stars that are usually about half the mass of our Sun — when they picked up some unique radio waves coming from a part of the sky where a star named Ross 128 is located. The pulsing signals appeared to be coming from deep space, possibly from the red dwarf. But the wave patterns don’t really match anything the astronomers would expect from the star, leaving them stumped as to the signal’s origins. The structure of the signal suggests the waves are coming from deep space, according to Abel Méndez, director of the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo, and his team.

That’s confusing, because there’s no foolproof explanation for the source. It’s possible the signal is caused by solar flares from Ross 128, which is a very active star that flares frequently. However, radio signals from flares are usually at much lower frequencies than the ones detected by Arecibo. The waves could be coming from something else in deep space within the field of view of Ross 128. But there isn’t anything nearby. “So right now we don’t have a theory to say how this star could do this,” says Méndez.

The red dwarfs observed by Arecibo, including Ross 128.
Image: Arecibo

Méndez and his team aren’t ruling out a local source, however. Unusually, in this instance, they can’t tell what the origin is — whether it’s Earth or space. The weird signal could be nearby radio interference, but local radio waves usually have easily identifiable patterns. It’s possible the signal is coming from a satellite orbiting Earth, but that would still be weird because no satellites have ever produced signals like this one before, according to Méndez. “Interference can bounce between the mountains and buildings and cause strange things,” he says. “Never like this, though.”

However, Méndez and his team are fairly sure that these waves are coming from deep space given the structure of the signal. Each radio wave has its own frequency — how much the wave moves up and down in a given period of time. Typically, communications signals from Earth are set at just one frequency. To find your favorite radio station, for instance, you have to tune your radio to the right frequency the station is broadcasting in. But the signal from Ross 128 contains waves of many different frequencies, and these waves arrived at different times here on Earth.

That’s a clue indicating that the signal traveled a long time through space. A radio wave traveling on its way to Earth will encounter tiny particles in interstellar space, causing lower frequencies to slow down and arrive later than higher frequencies. It’s an effect known as dispersion, and it becomes more pronounced the longer a signal has been traveling through space. The Ross 128 signal showed this type of dispersion, too.

Certain things — solar flares, for instance — have signatures scientists know to expect, but the signal from Ross 128 isn’t like any previous solar flare. It could be an entirely new type of solar flare never seen before. Of course, there is always the tantalizing option of aliens, but Méndez notes that theory is “at the bottom of many other better explanations.”

The good news is we may have part of this mystery solved soon. On Sunday, Méndez and his team at Arecibo got a chance to observe the star again, two months after the first signals were detected. They’ll be poring over that new data this week, and they hope to have details either this weekend or early next week. They’re optimistic the data they received will help them to parse out where the signal is coming from. Once they figure that out, then they can start to get to work explaining the cause of the waves. “We’re rushing this because we want to know,” says Mendez.

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