Astronomers discover new type of astral object

A new stellar object – only the second of its kind – has been found by an international team led by radio astronomers which might change our understanding of neutron stars – some of the densest and most extreme objects in the universe.

Results published in Nature detail how GPM J1839−10, a stellar object 15,000 lightyears away in the Scutum constellation, is breaking known rules about astronomical bodies.

Leading the research were astronomers from Western Australia’s Curtin University node of the International Centre for Radio Astronomy Research (ICRAR).

Like a type of neutron star called a magnetar, GPM J1839−10 emits extremely strong magnetic fields which produce powerful bursts of energy which can be detected on Earth as radio waves. But, unlike known magnetars – which themselves are rare – this star is not producing bursts every few seconds or minutes, but 22 minutes apart.

White spider like structures under night sky
An artist’s impression of the Murchison Widefield Array radio telescope observing the ultra-long period magnetar. Credit: ICRAR.

Only one other object like it is known and was discovered by the same researchers from Australia’s Curtin University. That stellar body was found in data from the Murchison Widefield Array (MWA) radio telescope in Western Australia. It emitted radio bursts every 18 minutes and was described in a Nature paper in January 2022.

That “long-period magnetar” stopped pulsing soon after it started. So the researchers went on a hunt for more like it.

Their wish was granted after searching the skies between June to September 2022 with the MWA, eventually finding GPM J1839−10. They checked their results with the Australian Square Kilometre Array Pathfinder, Parkes Observatory in Murriyang, NSW, and South Africa’s MeerKAT Radio Telescope.

Going back in archived data from the Very Large Array in the US and the Giant Metrewave Radio Telescope in India, they found that GPM J1839−10 has been pulsing since 1988. But the newly discovered source has such a slow period that, according to the best astrophysical models, it shouldn’t be emitting radio waves.

View over australia showing telescopes in boxes and wavy lines to star
The magnetar was discovered by the Murchison Widefield Array (MWA) radio telescope, with a host of other facilities around the globe. Credit: South African Radio Astronomy Observatory (SARAO), Gran Telescopio Canarias, Daniel López/IAC, Murchison Widefield Array, Marianne Annereau, Giant Metrewave Radio Telescope, NCRA, Australian SKA Pathfinder, CSIRO/Dragonfly Media, Australia Telescope Compact Array, CSIRO, Parkes Radio Telescope, Murriyang – CSIRO, Very Large Array, AUI/NRAO, XMM-Newton, European Space Agency.

“It’s producing these bright radio waves, and has been doing so for over 30 years, and we don’t really understand how,” says lead author Dr Natasha Hurley-Walker from Curtin University. “It rules out our previous hypothesis that it was some kind of magnetar, because these things should only persist for a short time. And yet this thing has been going on for a long time.”

So, if it’s not a magnetar, what is it? The researchers aren’t sure.

One possibility is that the star is a white dwarf – another stellar remnant which evolves out of the death of a lower mass star like our Sun.

“Recently, a white dwarf pulsar was detected spinning every 10 seconds or so. And as its beam crossed our line of sight, we see a little pulse. The problem is this, this is about 1000 times less luminous than our source. But that’s the best next best theory there. Other theories are ruled out by the data,” Hurley-Walker says.

“That’s why it’s quite exciting,” Hurley-Walker adds. “We’ve tried a bunch of different theories, and none of them really fit the data. People will be working on this, so I think this will be very exciting for the theory community.”

Further observations, including in different wavelengths using telescopes around the world, may solve the mystery of GPM J1839−10.

Illuminating what is behind this strange new stellar object may also help astronomers and astrophysicists understand other enigmatic phenomena like fast radio bursts, and the physics of neutron stars and magnetars.

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