Novel object in the constellation Shield

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Artist’s impression of the extremely long-period magnetar - a rare type of
Artist’s impression of the extremely long-period magnetar - a rare type of star with extremely strong magnetic fields that can produce violent bursts of energy. © ICRAR

The star could be a magnetar with properties that have yet to be explained

A new type of stellar object could challenge our understanding of neutron stars. An international team, including researchers from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has discovered a celestial body in the constellation Shield (Scutum) that could be an ultralong-period magnetar, a rare type of star with extremely strong magnetic fields that can produce violent bursts of energy. All magnetars known to date release energy at intervals of a few seconds to a few minutes. The newly discovered object emits radio waves every 21 minutes, which would make it the magnetar with the longest period ever discovered.

Rotating neutron stars have magnetic fields that are more than a billion times stronger than the strongest magnetic fields produced on Earth. An unusual example of such a magnetar may now have been discovered by an international team led by Natasha Hurley-Walker of Curtin University and the ,,International Centre for Radio Astronomy Research " in Australia. The researchers observed the novel star with the ,,Murchison Widefield Array" (MWA) in Western Australia at a distance of 15,000 light-years in the direction of the constellation Shield and named it GPM J1839-10. If it is indeed a magentar, it would be only the second star of this type with an extremely long rotation period known so far. The object, described as enigmatic and transient, appears in observations at regular intervals, emits powerful energy beams three times an hour, and disappears again.

"This remarkable object challenges our understanding of neutron stars and magnetars, which are among the most exotic and extreme objects in the universe," says Natasha Hurley-Walker. "The first of these enigmatic transient objects took us by surprise. We were baffled and started looking for similar objects to see if it was an isolated event or just the tip of the iceberg."

Five-minute energy bursts

Scanning the sky with the MWA telescope, the team soon discovered GPM J1839-10, an object that emits energy bursts lasting up to five minutes, five times longer than the first such object. Subsequent observations with other telescopes confirmed the discovery and provided details about the magnetar’s unique properties.

"GPM J1839-10 is a rather intriguing source that appears to be spinning too slowly to be a typical radio pulsar, but also radiates too stably to be a radio magnetar. To understand the true nature of this source, we sampled the signal every few milliseconds with the high-resolution instruments developed by our team to search for pulsars and fast transients," adds Ewan Barr of the Max Planck Institute for Radio Astronomy, a co-author of the paper. "The observations revealed a fine pulsar substructure that exhibits quasi-periodic oscillations. Whether these are an intrinsic property of the source or its environment remains to be determined."

A magnetar that should not exist

The team has also begun searching the observation archives of the world’s major radio telescopes for more information about the source. "The magnetar showed up in observations from the Giant Metre wave Radio Telescope in India, and the Very Large Array in the U.S. had observations going back to 1988," explains Natasha Hurley-Walker. "That was a pretty incredible moment for me. I was five years old when our telescopes first recorded pulses from this object, but no one noticed, and it remained hidden in the data for 33 years."

Not all magnetars produce radio waves. Some lie below the so-called death line, a critical threshold below which the magnetic field of a neutron star becomes too weak to produce radio waves. Since GPM J1839-10 is well below the death line, it should be spinning too slowly to generate radio pulses. But in fact, the source has been emitting radio wave pulses regularly for at least 33 years. Whatever mechanism may be behind it, it must be extraordinary. The discovery has important implications for understanding the physics of neutron stars and the behavior of magnetic fields in extreme environments. It also raises new questions about the formation and evolution of magnetars and may shed light on the origin of puzzling phenomena such as fast radio bursts.

The research team plans to make further observations of the magnetar to learn more about its properties and behavior. They hope to discover more magnetars with extremely long periods in the future, which could help refine our understanding of these fascinating and enigmatic objects.

Ultra-Long Period Magnetar

Animation/video sequence of the ultra-long period magnetar