Astronomers Have Detected The Brightest-Ever Pulsar Outside Our Galaxy
Astronomers have confirmed that an object they thought was a distant galaxy is actually the brightest extra-galactic pulsar ever seen. The team made the discovery using a technique that blocks a particular type of polarized light, similar to polarized sunglasses, which could be used to spy more ‘hidden’ pulsars. The newly detected pulsar, designated PSR J0523−7125, turns out to be a highly circularly polarized and variable radio source.
Pulsars are highly magnetized, rotating neutron stars emitting a beam of electromagnetic radiation. They are usually detected in the form of short bursts of radio emission; however, some of them are also observed via optical, X-ray and gamma-ray telescopes. One method to find new pulsars is to search for them in continuum surveys and identify them through circularly polarized emission. The new pulsar is in the Large Magellanic Cloud (LMC), and is quite different from most known pulsars. Its pulse is very wide — more than twice the size of other known pulsars in the LMC, and it is exceptionally ‘bright’ on the radio spectrum. A newfound pulsar is more than 10 times brighter than any other rapidly rotating stars we know of.
There are more than 3,300 radio pulsars known. Of these, 99 percent reside within our galaxy. Many were discovered with CSIRO’s famous Parkes radio telescope, Murriyang, in New South Wales. About 30 radio pulsars have been found outside our galaxy, in the Magellanic Clouds. So far, we don’t know of any in more distant galaxies. Astronomers search for pulsars by looking for their distinctive repeating signals in radio telescope data. This is a computationally intensive task. It works most of the time, but this method can sometimes fail if the pulsar is unusual: such as very fast, very slow, or (in this case) if the pulse is very wide. Because of its unusual properties, this pulsar was missed by previous studies, despite how bright it is. Pulsars are typically identified from their faint pulse, flickering periodically. But in the case of PSR J0523−7125, its pulse is so wide and bright, that it didn’t fit the typical profile of a pulsar and was dismissed as a galaxy. The researchers noted that the wide pulse profile of PSR J0523−7125 also suggests that it could be an aligned rotator. They added that the strong variability of this pulsar is likely caused by scintillation effects; however, other explanations cannot be excluded.
Although scientists have discovered more than 3,300 radio pulsars since the 1960s, only 1% of those are known outside the galaxy. Moreover, many of the discoveries come from a single radio telescope: Australia's Parkes Observatory, which is operated by the Australian government's Commonwealth Scientific and Industrial Research Organisation (CSIRO). (This telescope is also famous for receiving video of Apollo 11 footsteps on the moon.)
While extra-galactic pulsars are still a relative rarity, our ability to discover them – and other kinds of pulsars that are hard to find via traditional methods – should only increase from this point, thanks to the increasing availability of large-scale radio continuum surveys and future telescopes, such as the upcoming Square Kilometre Array project being built in South Africa. With improved instruments in the Square Kilometre Array era, instantaneous large fields-of-view and great sensitivity will be even more common, leading to the detection of large numbers of radio sources across the sky. Improved next-generation radio telescopes and increasing number of large-scale multi-wavelength surveys will bring large amounts of data with great sensitivity and resolution, giving us an unprecedented opportunity to identify more pulsar (even for extragalactic pulsars farther than the Magellanic Clouds).