The brightest extragalactic pulsars have been found in the Great Magellanic Cloud. Image source: Pennock
Astronomers have confirmed that what they thought was an object from a distant galaxy was actually the brightest pulsar outside the Milky Way to date. The team discovered this phenomenon using a technique capable of blocking a special type of polarized light, similar to polarized light sunglasses, that could be used to detect more “hidden” pulsars.
Pulsars are highly magnetized spin neutron stars formed by the collapsing remnants of exploding stars. As pulsars rotate, they emit radio waves from the poles — a type of “pulse” that can be detected with a radio telescope. Astronomers use pulsars to test gravitational theories and look for evidence of gravitational waves.
The new pulsar, named PSR J0523-7125, is located in the Great Magellanic Cloud (LMC) and is very different from most known pulsars. Yuanming Wang, an astrophysicist at australia’s Commonwealth Scientific and Industrial Research Organisation, said its pulses were very wide, more than twice that of other known pulsars in LMC and unusually “bright” on the radio spectrum.
Wang and his team say the pulsar is 10 times brighter than any other pulsar found outside the Milky Way. The research was recently published in the Astrophysical Journal.
“Due to its unusual nature, this pulsar was ignored by previous studies, although it was bright.” Paper co-author Tara Murphy, a radio astronomer at the University of Sydney in Australia, said in a press release.
Pulsars are usually identified by their faint pulses that flicker periodically. But in the case of PSR J0523?7125, its pulses are too wide and too bright to fit the typical outline of a pulsar and are therefore considered a galaxy.
Wang and an international team of astronomers first suspected from data from the Variable and Slow Transient survey that the object might be a pulsar. The survey was conducted using the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, which studied a large number of highly variable radio wave sources in the sky and collected data such as circular polarization.
The radiation of pulsars is usually highly polarized, with some oscillating in a circular fashion. Few space objects are polarized like this, which makes them stand out.
By using a computer program, the team was able to shield light from non-circular polarization wavelengths, revealing rare types of pulsars. Other telescopes, including the Mongoose Radio Astronomical Telescope in South Africa, have also confirmed their findings.
“We look forward to using this technique to discover more pulsars.” This is the first time we have been able to look for the polarization of pulsars in a systematic and conventional manner. Murphy said.
Yvette Cendes, a radio astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, says radio astronomy is not as effective as optical astronomy in discovering “transient” objects. Transient objects are space objects like pulsars. “But just because you’ve discovered a transitory object doesn’t mean it’s easy to figure out what it is.” Polarization data helps narrow down the source of the object, she said, suggesting that the technology has the potential to identify other transients in the future.
Although other telescopes are also collecting polarization data, large-scale radio measurements using circular polarization technology are a minority. In March, researchers used data from the Netherlands Low Frequency Array (LOFAR) telescope to discover two new pulsars, a technique they detailed in a preprint published on arXiv2. (Source: China Science Daily, Li Muzi)
Related paper information:https://doi.org/10.1051/0004-6361/202142636