"Impossible" neutron star spins too slowly and emits 7 types of signals
Astronomers have discovered a super strange neutron star that challenges our understanding of them – but may help unlock the mystery of fast radio bursts (FRBs). The object spins far slower than any other known neutron star, and gives off seven distinct types of radio pulses.
Neutron stars are the dense cores left behind after massive stars explode as supernovae, and some of them are known to throw off beams of radiation from their poles. If these beams just so happen to swing past Earth, they appear to us as brief, regular pulses of radio emissions, earning them the name “pulsars.”
Most pulsars spin extremely quickly, on the scale of milliseconds to a few seconds, with the slowest previously known taking 23.5 seconds per rotation. But the newly discovered pulsar spins at a snail’s pace of once every 75.88 seconds, making it by far the slowest radio-emitting neutron star found yet.
That sluggishness isn’t just a curiosity – it should be an impossibility. It’s long been thought that neutron stars produce their radio emissions as a direct result of their fast spins, and as they slow down over time, those emissions were expected to stop. But at well over a minute per rotation, this new pulsar challenges the models of this process, with the team admitting they aren’t sure how its emissions are generated.
Weirder still, the team found that the object gave off seven different types of pulses. “Normal” ones would rise to a peak brightness and then fade, while some pulses would have two or three peaks before fading out. Others still would be far more up-and-down in their brightness, giving the graph a “spiky” appearance. This means the object has an odd mix of characteristics from pulsars, ultra-long period magnetars and fast radio bursts, which could ultimately lead to answers for how they’re all related.
The pulsar, designated PSR J0901-4046, was originally discovered by astronomers using the MeerKAT radio telescope in South Africa, when one of its pulses showed up in an image. After that, its existence as a radio-emitting neutron star was confirmed from multiple pulses captured in a series of eight-second-long images. Its slow pulsing is how it likely eluded detection for so long, and it suggests there might be plenty more of them out there.
“Amazingly we only detect radio emission from this source for 0.5 percent of its rotation period,” said Dr. Manisha Caleb, corresponding author of the study. “It is therefore likely that there are many more of these very slowly spinning stars in the galaxy, which has important implications for understanding how neutron stars are born and age. The majority of pulsar surveys do not search for periods this long, so we have no idea how many of these stars might exist.”
The research was published in the journal Nature Astronomy.
Source: University of Sydney