A bright spot that scientists once wrote off as a distant galaxy may be the brightest pulsar ever detected outside the Milky Way.
Named PSR J0523−7125 and located at approximately 160,000 light years from Soil in the Large Magellanic Cloud (a satellite galaxy orbiting the Milky Way), the newly defined pulsar is twice as wide as any other pulsar in the region, and 10 times brighter than any known pulsar outside our galaxy. In fact, the object is so large and bright that researchers originally interpreted it as a distant galaxy, but new research released on May 2 in the Astrophysical Journal Letters suggests that this is not the case.
Using the Australian Square Kilometer Array Pathfinder (ASKAP) radio telescope in Western Australia, the study authors looked at space through special “sunglasses” that block all wavelengths of light except a specific type of emission associated with pulsars, the highly magnetized shells of stars. When PSR J0523−7125 appeared bright and clear in the results, the team realized that they were not looking at a galaxy at all, but at the pulsating corpse of a dead star.
“This was a wonderful surprise,” lead study author Yuanming Wang, an astrophysicist at the Australian Commonwealth Scientific and Industrial Research Organization (CSIRO) said in a statement† “I didn’t expect to find a new pulsar, let alone the brightest. But with the new telescopes we have access to now, like ASKAP and its sunglasses, it’s really possible.”
Pulsars are highly magnetized, rapidly spinning remnants of exploded stars. As they spin, flow radio waves burst from their poles, pulsing like lighthouse beams as those radio waves flash toward Earth.
The radio waves emitted by pulsars differ from many other cosmic light sources in that they can be circularly polarized — that is, the light’s electric field can rotate in a circle as it propagates. This unique polarization could give scientists a big clue in the tricky game of distinguishing pulsars from other distant light sources. In their new study, researchers used a computer program to filter out circularly polarized light sources from an ASKAP survey of pulsar candidates.
The team found that the presumed galaxy PSR J0523-7125 emitted circularly polarized light, meaning it is almost certainly a pulsar. And because pulsars are incredibly small — usually packing the mass of a sun into a ball no wider than a city — that means the object must be much closer and much brighter than scientists previously thought. If this pulsar is indeed lurking in the nearby Large Magellanic Cloud, as the researchers suspect, it may be the brightest pulsar ever found outside the Milky Way.
That exceptional brightness explains why the object was mistakenly identified as a galaxy after its initial detection, the researchers said. And by filtering circularly polarized light from future star surveys, researchers may be able to unmask even more unusual pulsars hiding in plain sight.
“We would expect to find more pulsars with this technique,” study co-author Tara Murphy, a radio astronomer at the University of Sydney in Australia, said in the statement. “This is the first time we have been able to search for the polarization of a pulsar in a systematic and routine way.”
Originally published on Live Science.
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