Radio astronomers see what the naked eye can’t. As we study the sky with telescopes that record radio signals rather than light, we end up seeing a lot of circles.
The newest generation of radio telescopes – including the Australian Square Kilometre Array Pathfinder (ASKAP) and MeerKAT, a telescope in South Africa – is revealing incredibly faint cosmic objects, never before seen.
In astronomy, surface brightness is a measure that tells us how easily visible an object is. The extraordinary sensitivity of MeerKAT and ASKAP is now revealing a new “low surface brightness universe” to radio astronomers.
It’s comprised of radio sources so faint they have never been seen before, each with their own unique physical properties.
Many of the ASKAP results presented here were obtained with one of its major observing programs called EMU (Evolutionary Map of the Universe).
EMU is mapping the entire southern sky with an unprecedented sensitivity and will deliver the most detailed map of the Southern Hemisphere sky to date – a spectacular new radio atlas that will be used for decades to come.
EMU’s all-hemisphere coverage paired with ASKAP’s exceptional sensitivity, especially within the Milky Way, is what’s yielded so many recent discoveries.
Here’s what they’re teaching us.
Unstable stars
The ghostly ring Kýklos (from the Greek κύκλος, circle or ring) and the object WR16 both show the environment of rare and unusual celestial objects known as Wolf-Rayet stars.
When big stars are close to running out of fuel, they become unstable as they enter one of the last stages of the stellar life cycle, becoming a Wolf-Rayet star. They begin surging and pulsing, shedding their outer layers which can form bright nebulous structures around the star.
In these objects, a previous outflow of material has cleared the space around the star, allowing the current outburst to expand symmetrically in all directions. This sphere of stellar detritus shows itself as a circle.
Exploded stars
Stingray 1, Perun, Ancora and Unicycle are supernova remnants. When a big star finally runs out of fuel, it can no longer hold back the crush of gravity. The matter falling inwards causes one final explosion, and the remains of these violent star deaths are known as supernovas.
Their expanding shockwaves sweep up material into an expanding sphere, forming beautiful circular features.
The supernova remnant will be deformed by its environment over time. If one side of the explosion slams into an interstellar cloud, we’ll see a squashed shape. So, a near-perfect circle in a messy universe is a special find.
Teleios – named from the Greek Τελεɩοσ (“perfect”) for its near-perfectly circular shape – is shown below. This unique object has never been seen in any wavelength, including visible light, demonstrating ASKAP’s incredible ability to discover new objects.
The shape indicates Teleios has remained relatively untouched by its environment. This presents us with an opportunity to make inferences about the initial supernova explosion, providing rare insight into one of the most energetic events in the universe.
At the other extreme, we can take an object and discover something entirely new about it. The Diprotodon supernova remnant is shown below.
This remnant is one of the largest objects in the sky, appearing approximately six times larger than the Moon. Hence the name: the animal Diprotodon, one of Australia’s most famous megafauna, a giant wombat that lived …
