Weird radio pulses could be coming from new type of stellar object

Astronomers puzzled over what is powering GPM J1839−10

Astronomers believe they may have discovered a new type of stellar object after spotting something that has been beaming radio pulses every 22 minutes for more than three decades.

The oddity, code named GPM J1839−10, lies about 15,000 light-years away, and was detected by an international team of researchers. They were searching the skies for objects that periodically emitted bright beams of electromagnetic energy after they came across something that would flash three times an hour before going quiet.

"We were stumped," Natasha Hurley-Walker, first author of the new research published in Nature and a senior lecturer at Curtin University in Australia, said in a statement. "So we started searching for similar objects to find out if it was an isolated event or just the tip of the iceberg."

The team spotted GPM J1839−10 with the Murchison Widefield Array, a radio telescope made up of a 4,094 ground-based antenna system in Wajarri Yamaji Country in outback Western Australia. It releases a burst of radio waves lasting from 30 seconds to five minutes, every 22 minutes, a signal five times longer compared to the initial object reported in a previous study in Nature.

They found that other observatories had previously spotted the same repetitive signal, but no one had bothered to study it further until now. "It showed up in observations by the Giant Metrewave Radio Telescope in India, and the Very Large Array (VLA) in the USA had observations dating as far back as 1988," Hurley-Walker said.

"That was quite an incredible moment for me. I was five years old when our telescopes first recorded pulses from this object, but no one noticed it, and it stayed hidden in the data for 33 years," she said. "They missed it because they hadn't expected to find anything like it." GPM J1839−10 behaves like magnetar, a type of neutron star, the leftover compressed core of a dead star, that spins and has a magnetic field over a trillion times stronger than Earth's.

But it has strange properties that don't seem to fit with other magnetars. Over time, the magnetic field of magnetars decays and it starts rotating more slowly. The magnetic field powers the release of electromagnetic energy, and GPM J1839−10 appears to be spinning too slowly to produce the energy observed.

"The object we've discovered is spinning way too slowly to produce radio waves – it's below the death line," Hurley-Walker said. "Assuming it's a magnetar, it shouldn't be possible for this object to produce radio waves. But we're seeing them." The archival data shows that some mechanism is powering GPM J1839−10's period release of energy, but the researchers don't understand it yet.

They reckon its weird behavior shows it is a different type of magnetar, and possibly a completely new stellar object. It could be an ultra-long period magnetar, for example, possibly the second of its kind found to date. Although the team aren't quite sure what it is, they believe GPM J1839−10 could provide more details on other types of mysterious phenomena like fast radio bursts.

The only way to study the object further is to try to find more of them in space. "Every 22 minutes, it emits a five-minute pulse of radio wavelength energy, and it's been doing that for at least 33 years. Whatever mechanism is behind this is extraordinary," Hurley-Walker concluded. ®

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