![]() Telescopes working at other wavelengths can serve as another pair of eyes to help us find new clues.Īfter the MeerKAT detection, we searched for the source in X-rays (using the space-based Neil Gehrels Swift Observatory and Chandra X-ray Observatory) and infrared (using the Gemini telescope in Chile). It is always a good idea to investigate from multiple perspectives. Radio lightcurve showing how ASKAP J173608.2-321635 varies with time. Author provided ![]() The source disappeared in the course of a single day, even though it had lasted for weeks in our previous ASKAP observations. Luckily, the signal returned, but the behaviour of the source was now dramatically different. Because the signal was intermittent, we observed it for 15 minutes every few weeks, hoping we would see it again. We then tried the more sensitive MeerKAT radio telescope in South Africa. However, these observations yielded nothing. We next observed the source with the Parkes radio telescope in New South Wales to decide whether it was a pulsar. We need evidence to determine what it is.īased on our ASKAP data, we thought the new object might be a pulsar or a flaring star: both types of object can be polarised, and change in brightness. Investigating a new astronomical object is a bit like a detective job. Almost all of them are sources we understand well, such as pulsars (the rapidly rotating, highly magnetised remnants of exploded stars) or highly magnetised red dwarf stars. Polarised radio sources are extremely rare: we might find fewer than ten circularly polarised sources out of thousands. ![]() Our eyes cannot distinguish between polarised and unpolarised light, but ASKAP has the equivalent of polaroid sunglasses for radio waves. The small insets show the source turning off and on in images from the MeerKAT telescope. Author providedĪs well as changing over time, the signal was circularly polarised. ASKAP image of the Galactic Centre region. This object was unique in that it started out invisible, became bright, faded away, and then reappeared. When we looked towards the centre of our galaxy (the Milky Way), we found a source we called ASKAP J173608.2-321635 (this catchy name comes from its coordinates in the sky). The past decade has seen thousands of transients discovered at optical and X-ray wavelengths, but radio wavelengths are largely untapped. Transients are usually connected with some of the most energetic and violent events in the Universe, such as the death of massive stars. That’s why objects that do change (known as variables) or appear and disappear (known as transients) are so interesting. Most things astronomers see in outer space are fairly stable and don’t change much on human time scales. We have been surveying the sky with ASKAP throughout 20 in search of unusual new objects, in a project called the Variables and Slow Transients (VAST) survey. A strange signal from the heart of the Milky Way Despite our best efforts, we are still unable to work out exactly what produced these mysterious radio waves. We first spotted the signal using the Australian Square Kilometre Array Pathfinder Telescope (ASKAP), then followed up with other telescopes around the world and in space. What’s more, the radio waves in the signal had an uncommon “circular polarisation”, which means the electric field in the radio waves spirals around as the waves travel through space. The signal blinked on and off, growing 100 times brighter and dimmer over time. In early 2020, we detected an unusual radio signal coming from somewhere near the centre of our galaxy.
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