“We’ve never seen anything like it,” says Ziteng Wang, a doctoral student at the University of Sydney’s School of Physics and the author of a new study that reveals the discovery of very unusual radio signals coming from the center of the galaxy. It is a type of wave that does not conform to any known pattern and could come from some new class of stellar object.
“It is a signal with a very high polarization,” explains the scientist. “This means that its light oscillates in only one direction, but that direction rotates over time. Furthermore, the brightness of the object also varies drastically, by a factor of one hundred, and the signal turns on and off seemingly randomly. “
The discovery has been published in the Astrophysical Journal . “At first we thought it could be a pulsar, a very dense type of spinning dead star, or a type of star that emits huge solar flares. But the signals from this new source do not match what we expect from this type of celestial object, ”explains Wang.
Thanks to the tremendous advances in radio astronomy in recent times, a wide field of study has been opened that helps us reveal the secrets of the universe by studying the radio waves emitted by transient objects such as pulsars and supernovae.
In this case, the international team of scientists discovered the object using CSIRO’s ASKAP radio telescope in Western Australia. Follow-up observations were made with the MeerKAT telescope of the South African Radio Astronomy Observatory.
An extraordinary behavior
“Throughout 2020 and 2021 we have been surveying the sky with ASKAP to find new unusual objects with a project known as Variables and Slow Transients (VAST),” explains Tara Murphy, also from the Sydney Institute of Astronomy. “Looking towards the center of the galaxy we find ASKAP J173608.2-321635, named for its coordinates. This object was unique in that it started out invisible, turned bright, faded, and then reappeared. This behavior was extraordinary ”.
After detecting six radio signals from the source over nine months in 2020, astronomers tried to find the object with visual light. They found nothing.
They tried it with the Parkey radio telescope and were also unable to find the source. “We then tested the more sensitive MeerKAT radio telescope in South Africa. Because the signal was intermittent, we were looking for it every fifteen minutes every few weeks, hoping to see it again, ”says Murphy. “Fortunately, the signal returned, but we found that the behavior was different from what we had observed months ago: the source disappeared in a single day, even though it had lasted for weeks in our previous ASKAP observations .”
David Kaplan, a researcher at the University of Wisconsin-Milwaukee, explains: “The information we have has some parallels with another emerging class of mysterious objects known as Radio Transients of the Galactic Center , including one called the ‘cosmic burper’. Although our new object, ASKAP J173608.2-321635, shares some properties with them, there are also differences ”.
Scientists will continue to closely monitor the object for new clues to help solve the mystery. “In the next decade, the Square Kilometer Array (SKA) transcontinental radio telescope will be online. You will be able to make sensitive maps of the sky every day, ”says Murphy. “We hope that the power of this telescope will help us solve mysteries like this latest discovery.”
Referencia: Wang et al. 2021. Discovery of ASKAP J173608.2-321635 as a Highly-Polarized Transient Point Source with the Australian SKA Pathfinder. The Astrophysical Journal. DOI: 10.3847/1538-4357/ac2360
