Artists impression of the oscillating, variable radio signal ASKAP J173608.2-321635 coming to Earth from towards the center of the Milky Way. Credit: Sebastian Zentilomo/University of Sydney
In early 2020, we found an uncommon radio signal coming from someplace near the center of our galaxy. The signal blinked on and off, growing 100 times brighter and dimmer in time.
Whats more, the radio waves in the signal had an unusual “circular polarisation,” which implies the electric field in the radio waves spirals around as the waves travel through area.
We initially found the signal utilizing the Australian Square Kilometre Array Pathfinder Telescope (ASKAP), then followed up with other telescopes around the globe and in space. Despite our best efforts, we are still unable to exercise exactly what produced these mysterious radio waves.
A strange signal from the heart of the Milky Way
We have been surveying the sky with ASKAP throughout 2020 and 2021 looking for unusual brand-new items, in a task called the Variables and Slow Transients (VAST) study.
Many things astronomers see in outer space are relatively stable and do not alter much on human time scales. Thats why items that do alter (called variables) or appear and vanish (known as transients) are so interesting.
Transients are usually gotten in touch with a few of the most energetic and violent occasions in deep space, such as the death of huge stars. The previous decade has seen thousands of transients found at optical and X-ray wavelengths, however radio wavelengths are mainly untapped.
ASKAP image of the Galactic Centre area. The little insets show the source shutting off and on in images from the MeerKAT telescope. Credit: Author provided
When we looked towards the center of our galaxy (the Milky Way), we found a source we called ASKAP J173608.2-321635 (this catchy name originates from its coordinates in the sky). This things was distinct in that it started out undetectable, ended up being brilliant, faded away, and then reappeared. This habits was amazing.
In addition to altering gradually, the signal was circularly polarised. Our eyes can not identify between polarized and unpolarized light, but ASKAP has the equivalent of polaroid sunglasses for radio waves.
Polarised radio sources are incredibly uncommon: we might discover less than 10 circularly polarised sources out of thousands. Practically all of them are sources we understand well, such as pulsars (the rapidly turning, extremely magnetized residues of exploded stars) or extremely magnetized red dwarf stars.
Finding more proof
Investigating a new astronomical things is a bit like a detective task. We require proof to determine what it is.
Based on our ASKAP information, we believed the brand-new things may be a pulsar or a flaring star: both kinds of things can be polarised, and change in brightness. Nevertheless, we required to find more ideas.
We next observed the source with the Parkes radio telescope in New South Wales to decide whether it was a pulsar. These observations yielded absolutely nothing.
We then attempted the more sensitive MeerKAT radio telescope in South Africa. The source disappeared in the course of a single day, even though it had actually lasted for weeks in our previous ASKAP observations.
Radio lightcurve revealing how ASKAP J173608.2-321635 differs with time. Credit: Author supplied
It is constantly a good concept to examine from several viewpoints. Telescopes operating at other wavelengths can act as another pair of eyes to assist us find new clues.
After the MeerKAT detection, we browsed for the source in X-rays (utilizing the space-based Neil Gehrels Swift Observatory and Chandra X-ray Observatory) and infrared (utilizing the Gemini telescope in Chile). We saw nothing.
Still a mystery
We have observed this odd item at numerous wavelengths utilizing telescopes on 3 continents and in area. What can we state about what it actually is?
Can it be a star? It seems not likely since stars likewise discharge much of their light in the optical and infrared (like the Sun), but we spot nothing at these wavelengths.
Can it be a pulsar? Like our signal, pulsars produce polarised radio waves and can vary considerably in brightness. However the attribute of pulsars is quick pulses in between milliseconds to seconds long, and we did not find these with Parkes or MeerKAT.
Is the sources proximity to the center of our galaxy an idea? Over the previous 15 years, a number of appealing radio sources have been found towards the Galactic center (consisting of one dubbed the “cosmic burper”). We dont understand what they are, but they are imaginatively called Galactic Center Radio Transients (GCRTs).
Are they associated to ASKAP J173608.2-321635? Our signal is still a mystery.
We will keep observing this source in brand-new methods. It is simply the very first of numerous uncommon short-term sources that we expect to find with the powerful ASKAP selection, and it offers a tip of the future of radio astronomy.
Composed by:
When we looked towards the center of our galaxy (the Milky Way), we discovered a source we called ASKAP J173608.2-321635 (this appealing name comes from its collaborates in the sky). We then tried the more delicate MeerKAT radio telescope in South Africa. Like our signal, pulsars produce polarised radio waves and can vary dramatically in brightness. Over the previous 15 years, a number of appealing radio sources have actually been discovered toward the Galactic center (including one called the “cosmic burper”). We do not understand what they are, but they are imaginatively called Galactic Center Radio Transients (GCRTs).
Ziteng Wang– PhD researcher, University of Sydney
David Kaplan– Associate teacher of Physics, University of Wisconsin-Milwaukee
Tara Murphy– Professor, University of Sydney
This article was first released in The Conversation.
