A team of astronomers announces that they have detected a strange radio source coming from the center of the Milky Way. The signal repeats seemingly randomly and cannot be attributed to any known astronomical object, leading this team to believe that it may be evidence of a new phenomenon.
The signal was first detected in data dating back to April 2019 collected by the Australian Square Kilometer Array Pathfinder (ASKAP) Variables and Slow Transients (VAST) survey. This huge telescope scans the sky in search of radio sources associated with various astronomical objects and phenomena such as pulsars, magnetars, supernovae or gamma-ray bursts. However, this new detection did not match any of these.
Designated ASKAP J173608.2-321635 and coming from the direction of the galactic center, the signal repeated itself seventeen times in less than two years at random intervals. The brightness of this source, which is also polarized, can change dramatically, decreasing in a single day, but it can sometimes last for a few weeks.
Over the past few months, astronomers have started looking for the same signal from the MeerKAT observatory in South Africa. It was recovered on February 7, 2021, then in April from the Australian Telescope Compact Array (ATCA). By checking the archived radio readings of these telescopes, astronomers realized that no other such signals had been detected before April 2019. Likewise, nothing appeared there in the near infrared or in the X-ray domain. which would normally accompany radio signals for certain known objects.
Thus, these signals emanating from the galactic center do not match any known pattern . The researchers therefore obviously thought of a pulsar.
These dense objects, formed after the collapse of a massive star, rapidly rotate themselves by releasing electromagnetic signals into space. Such an object could explain the intermittent nature, polarization and variable brightness of this signal. However, pulsars tend to "blink" for seconds or milliseconds. This new source can in turn stay "on" for weeks at a time. We could possibly imagine a pulsar with an ultra-long rotation period , but it would be the first of its kind .
The magnetar hypothesis (pulsars with extremely strong magnetic fields) could also be ruled out since these objects are known to emit X-rays when active . However, this is not the case here.
This signal, however, shares some properties with a type of mysterious signal spotted near the galactic center . These are known as Galactic Center Radio Transients (GCRT). As their name suggests, these are short-lived flashing radio signals that originate near the center of the Milky Way. Three were identified in the 2000s and others are awaiting confirmation. However, again, it's not that simple.
"GCRTs are still a mystery “, emphasizes Ziteng Wang, the main author of this work. “They turn on and off erratically, are highly polarized, and are invisible in the X-ray or optical range. As all the sources received to date have been close to the galactic center, this source could therefore be a new GCRT. However, the time scale of this burst is not consistent. Also, they are usually discovered in lower frequencies. And we don't even know if all GCRTs share a common origin “.
So, for now, researchers are stalling to the point of considering a possible new class of astronomical objects. Additional observations will therefore be necessary to understand it. Astronomers plan to focus their analyzes away from the galactic center to see if the location of this signal is related to its nature or just a coincidence.
