Telescope "sunglasses" reveal brightest extragalactic pulsar ever found
Astronomers have discovered what may be the brightest pulsar in the sky. Despite its intense light the pulsar has long evaded detection, and was only revealed thanks to a telescope equipped with some cosmic “sunglasses.”
Pulsars are a type of neutron star that emit beams of radiation from their poles, creating pulses of light when these beams wash over Earth. These bright pulses flash quickly, with usually just seconds or milliseconds between them, making them relatively easy to spot in the cosmos.
The newly discovered pulsar, designated PSR J0523−7125, flashes three times per second, and is located in the Large Magellanic Cloud, a dwarf galaxy that orbits our own Milky Way. It also happens to be 10 times brighter than any other pulsar ever found outside our galaxy, and rivals the brightest of those found within it.
But if it’s so bright, how did it evade detection for so long? The researchers say this pulsar has an unusual feature that helped it stay hidden – its beams of radiation are very wide, meaning the pulses stay “on” for much longer than most pulsars. That means that surveys would overlook the light, assuming it was a distant background galaxy.
The pulsar was finally discovered using the ASKAP radio telescope in Australia, which uses a kind of filter the team describes as sunglasses. Thanks to their extreme magnetic fields, pulsars produce highly polarized light, which is indistinguishable from regular light to most instruments. ASKAP, however, can see it.
While studying ASKAP data, the researchers noticed a highly polarized object in the Large Magellanic Cloud that was changing its brightness over the course of months. Follow up observations with other instruments didn’t show any object in X-ray, optical or infrared wavelengths, but finally the MeerKAT radio telescope in South Africa confirmed it as an unusual pulsar.
“We should expect to find more pulsars using this technique,” said Professor Tara Murphy, lead author of the study. “This is the first time we have been able to search for a pulsar’s polarization in a systematic and routine way. Because of its unusual properties, this pulsar was missed by previous studies, despite how bright it is.”
The research was published in The Astrophysical Journal.