
Impression of neutron star ASKAP J1839-0756 emitting radio waves from its magnetic pole
james josephides
The collapse of a star some 13,000 light-years away is so rare that the researchers who discovered it say it shouldn’t exist at all.
It was first detected by the ASKAP radio telescope in Western Australia in January 2024, and is likely a type of pulsar never seen before.
When a supermassive star reaches the end of its life and explodes as a supernova, its remains form an ultra-dense object called a neutron star. A pulsar is a rapidly rotating neutron star that emits radio waves from its magnetic poles as it rotates. Most pulsars rotate at more than one revolution per second, and each time a radio beam is directed at us, we receive pulses of the same frequency.
But in recent years, astronomers have begun discovering compact objects that emit pulses of radio waves at much slower speeds. This perplexed scientists who thought the radio waves should stop flashing once the rotation slowed by more than a minute per revolution.
These slowly rotating objects are known as long-period radio transients. Last year, a team led by Manisha Caleb at the University of Sydney in Australia announced that they had discovered a transient with a period of 54 minutes.
Now, Caleb and his colleagues say the new object they discovered a year ago, named ASKAP J1839-0756, is rotating at a record-low 6.45 hours per revolution.
This is also the first transient phenomenon discovered in interpulses, which are weak pulses that come from opposite magnetic poles in the middle of the main pulse.
The research team initially thought that ASKAP J1839-0756 was a white dwarf, a small star similar to our deceased sun. “But we have never seen an isolated white dwarf emit a radio pulse, and our calculations show that, based on the nature of the pulse, it is too large to be an isolated white dwarf.” It turns out it’s too much,” says team member Joshua Lee from the University of Sydney. .
The researchers then thought it might be a magnetar, a neutron star with a massive magnetic field 10 trillion times more powerful than the most powerful MRI machine on Earth.
Similar magnetars with a rotation period of 6.67 hours have been discovered before, but so far they have only emitted X-rays rather than radio waves.
Caleb says that if the star is an isolated magnetar, it would be the first time it has emitted radio waves at such a slow frequency.
“This new object completely rewrites what we thought we knew about the mechanisms of radio emission from neutron stars over the past 60 years,” Caleb says. “This is definitely one of the strangest objects in recent years, because we never thought these objects existed. But now we’re finding them. If it is a magnetar, it is certainly unique among the neutron star population.
She says the idea that pulsars stop emitting radio waves if they spin too slowly needs to be reconsidered.
“In recent years, we have observed objects that appear to be beyond this line of death, but they are still emitting radio (frequencies),” Caleb says. “So they’re like zombie stars, you don’t expect them to be alive, but they’re still alive, they pulse, and they’re gone.”
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(Tag to translate) Astronomy