3 minute read
Slow-spinning radio neutron star breaks all the rules
from Contact 17
BY RACHEL RAYNER (CSIRO), MANISHA CALEB AND JOSHUA LEE (UNIVERSITY OF SYDNEY)
Most collapsed stars complete a rotation in seconds. This one takes nearly an hour.
Research from the University of Sydney and CSIRO, Australia’s national science agency, has uncovered the slowest long-period radio transient yet. Perhaps a neutron star, a magnetar, a white dwarf, or something else entirely, this cosmic lighthouse spins once every 6.5 hours. The previous record was just shy of one hour.
This discovery, found using CSIRO’s ASKAP radio telescope on Wajarri Country and published in Nature Astronomy, pushes the boundaries of what we thought possible for such objects, which typically rotate very quickly.
Neutron stars, such as pulsars, typically rotate in milliseconds. However, over the past three years a new type of radio transient object – so called because they are detected in radio waves – has been detected, which rotate much more slowly. The mechanisms that allow such a slowly rotating object to emit radio waves is completely unknown.
This slow lighthouse, called ASKAP J1839-0756, also happens to be aligned with Earth in a way that lets researchers see radio waves from both its magnetic poles. This rare phenomenon is a first for objects spinning this slowly.
During a routine observation, ASKAP J1839-0756 stood out because no object had previously been identified at that position. If the observation on this patch of sky had been made 15 minutes later, the team would have missed it.
Such a discovery is thanks to the telescope’s wide field of view and regular surveying of the sky, opening up the possibility of these serendipitous discoveries.
The next step is to work out what the object could be. One possibility is a magnetar – a type of neutron star that is the strongest magnet in the Universe. Magnetars generate radio pulses through a different mechanism to a pulsar, which might allow them to keep shining even at slower spin rates. But even magnetars have limits, and their periods are usually measured in seconds, not hours.
Another possibility is a white dwarf – the leftover core of a star less massive than those that form neutron stars. White dwarfs spin much more slowly than neutron stars, but no individual isolated white dwarfs have been observed to emit radio pulses. And so far no observations in other wavelengths have found evidence of a white dwarf at this location in the sky.
Whatever ASKAP J1839-0756 turns out to be, it is clear that this object is rewriting the rulebook. Its strange combination of slow rotation, radio pulses and interpulses is forcing astronomers to rethink the limits of neutron star behaviour and explore new possibilities.
The discovery of ASKAP J1839-0756 is a reminder that the Universe loves to surprise us, especially when we think we have got it all figured out. As the team continues to monitor this mysterious object, we’re bound to uncover more secrets.
