Astronomers have followed a mysterious radio signal from outer space to the discovery of a neutron star unlike any previously found.
The story begins with Manisha Caleb, a lecturer at the University of Sydney.
She and her colleagues were observing the Vela-X 1 region of the Milky Way – a part of space that’s around 1,300 light years away from Earth.
They were using the MeerKAT radio telescope in South Africa when they noticed a strange-looking flash or ‘pulse’ that lasted about 300 milliseconds.
‘The flash had some characteristics of a radio-emitting neutron star. But this wasn’t like anything we’d seen before,’ she said.
A neutron star is the collapsed remains of a massive supergiant star. Apart from a black hole, they are the smallest and densest stellar objects known to man.
When they’re especially dense, they can be called pulsars – and often emit bursts of radio waves that we can pick up here on Earth.
‘Our observation showed PSR J0941-4046 [which is what they named the star] had some of the characteristics of a “pulsar” or even a “magnetar”. Pulsars are the extremely dense remnants of collapsed giant stars which usually emit radio waves from their poles,’ explained Caleb.
‘As they rotate, the radio pulses can be measured from Earth, a bit like how you’d see a lighthouse periodically flash in the distance.
‘However, the longest known rotation period for a pulsar before this was 23.5 seconds – which means we might have found a completely new class of radio-emitting object. Our findings are published in Nature Astronomy.’
Inside a star graveyard
As well as finding a neutron star sending out pulses unlike anything we’ve seen before, the team also discovered it lies within a neutron star “graveyard.”
This particular region of space that PSR J0941-4046 exists in is believed to be filled with neutron stars at the end of their life cycle.
Some of them aren’t as active, while others may be completely dead and inert.
‘PSR J0941-4046 challenges our understanding of how neutron stars are born and evolve,’ Caleb said.
‘It’s also fascinating as it appears to produce at least seven distinctly different pulse shapes, whereas most neutron stars don’t exhibit such variety. This diversity in pulse shape, and also pulse intensity, is likely related to the unknown physical emission mechanism of the object.’
We’ll leave you to wonder about what she means by ‘unknown physical emission mechanism’.
Calbe continued: ‘One particular type of pulse shows a strongly “quasi-periodic” structure, which suggests some kind of oscillation is driving the radio emission. These pulses may provide us with valuable information about the inner workings of PSR J0941-4046.
‘These quasi-periodic pulses bear some resemblance to enigmatic fast radio bursts, which are short radio bursts of unknown origin.
‘However, it’s not yet clear whether PSR J0941-4046 emits the kind of energies observed in fast radio bursts.’
Of course, as with any deep space discovery, the scientists simply replace answers with more questions.
How long has this neutron star been active? Are there other stars like this one out in the galaxy? Is it even a neutron star in the classic sense or do we need to invent a new kind of object to classify it?
‘Detecting similar sources is challenging, which implies there may be a larger undetected population waiting to be discovered,’ Caleb said.
She concluded: ‘Our finding also adds to the possibility of a new class of radio transient: the ultra-long period neutron star. Future searches for similar objects will be vital to our understanding of the neutron star population.’
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