Astronomers have confirmed that an object they thought was a distant galaxy is actually the brightest extra-galactic pulsar ever seen. The team made this discovery using a technique that blocks a particular type of polarized light, similar to polarized sunglasses, which could be used to spy on more “hidden” pulsars.
Pulsars are highly magnetized spinning neutron stars that form from the collapsed remnants of exploded stars. As pulsars spin, they release a stream of radio waves from their poles – a “pulse” that can be detected using radio telescopes. Astronomers use pulsars to test theories of gravity and search for evidence of gravitational waves.
The new pulsar, called PSR J0523−7125, is about 50,000 parsecs from Earth in the Large Magellanic Cloud (LMC), and is quite unlike most known pulsars. Its pulse is very broad – more than double the size of other known LMC pulsars, and it is unusually “bright” on the radio spectrum, says Yuanming Wang, an astrophysicist at Australia’s Commonwealth Scientific and Industrial Research Organization in Canberra .
Wang and the team say the pulsar is ten times brighter than any other pulsar found outside the Milky Way. Their study is published in The Astrophysical Journal today1.
“Due to its unusual properties, this pulsar has been missed by previous studies, despite its luminosity,” co-author Tara Murphy, a radio astronomer at the University of Sydney in Australia, said in a press release.
Pulsars are usually identified from their faint, periodically flickering pulse. But in the case of PSR J0523−7125, its pulse is so broad and bright that it did not fit the typical profile of a pulsar and was rejected as a galaxy.
Wang and an international team of astronomers first suspected the object could be a pulsar in data from the Variables and Slow Transients survey, conducted using Australia’s Square Kilometer Array Pathfinder (ASKAP) telescope in Australia western. The survey examines a large amount of sky for widely varying radio wave sources and collects circular polarization, among other data.
Pulsar emissions are often highly polarized, and some of them oscillate in a circular fashion. Few space objects are polarized like this, which sets them apart.
Using a computer program, the team was able to block out wavelengths of light that weren’t circularly polarized, revealing the rare type of pulsar. Other telescopes, including the MeerKAT Radio Astronomy Telescope in South Africa, confirmed their discovery (see Hidden Pulsar).
“We should expect to find more pulsars using this technique. This is the first time we have been able to systematically and routinely search for the polarization of a pulsar,” Murphy said.
Yvette Cendes, a radio astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, says radio astronomy hasn’t been as good as optical astronomy at finding “transient” objects – space objects like pulsars that move in and out. of sight. “Surveys like VAST change that,” she says.
“But just because you find a transient [object] doesn’t mean it’s easy to figure out what it is,” she says. The polarization data helped narrow down the object’s source, suggesting the technique has the potential to identify other transients in the future, she says.
Although other telescopes collect polarization data, there have only been a few large-scale radio surveys using the circular polarization technique. In March, researchers using data from the Low-Frequency Array Telescope (LOFAR) in the Netherlands found two new pulsars using the technique, which they detailed in a preprint published on arXiv2.