A dead star appears to be dying again, say astronomers who have spotted a pulsar that is gradually losing its spin.
Pulsars are a form of neutron star, which are themselves the remnants of a massive star that reached the end of its life in a supernova explosion. They get their name because they spin rapidly, usually multiple times a second, releasing beams of radiation that appear to 鈥減ulse鈥� when viewed from Earth. It is thought that pulsars gradually slow down over time, eventually crossing a 鈥渄eath-line鈥� as their rotation reaches a low enough level, but this has never been observed.
Now, at the University of Sydney, Australia, and her colleagues say they have spotted an object called ASKAP J1935+214 that appears to be a pulsar spinning at a relatively measly 54 minutes per rotation, suggesting it is indeed dying for a second time. 鈥淭his object is in the neutron star graveyard,鈥� says Caleb.
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The team discovered the star in October 2022 using the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, and say it is around 16,000 light years away and probably 10 to 20 kilometres in diameter. The researchers have seen the star exhibit three distinct states: producing a strong pulse lasting tens of seconds, a weak one lasting hundreds of milliseconds and a completely resting mode with no pulses.
鈥淣o other object that we know of does this,鈥� says Caleb. 鈥淚f we had not pinpointed these emissions from the same object, we would not have believed it鈥檚 from the same point in the sky.鈥�
鈥淭his suggests that something is physically changing in the object that we do not understand,鈥� she says.
The only other possibility is that the object is a magnetic white dwarf, which is a star that hasn鈥檛 collapsed to the same density as a neutron star. However, researchers have never seen any radio emissions from a magnetic white dwarf, so Caleb says a neutron star is more likely, even if they don鈥檛 fully understand it.
鈥淲e are going to have to revisit our understanding of how neutron stars evolve,鈥� she says. 鈥淭his challenges our 60-year understanding of neutron star formation and evolution.鈥�
Nature Astronomy
