The Universe has found many dim round objects, spotted by the latest radio telescopes

The latest highly sensitive radio telescopes make it possible to detect what is hidden from observation in other ranges – in visible and infrared light. Some of the amazing objects in the radio range are dim round objects, the origin of which can be very different and not always clear. There have been dozens of such discoveries, and the list continues to grow.

Examples of round, faint radio objects in the Universe. Image credit: Miroslav Filipovic

The crowning achievement of the finds could be hypothetical Dyson spheres created by powerful alien civilizations. But scientists already have more than enough miracles. Especially since the new ASKAP radio telescope array in Australia has completed only 25% of the southern sky survey under the Evolutionary Map of the Universe (EMU) program. This will be a catalog of radio objects for decades to come, where there are enough astronomical mysteries for thousands of discoveries.

In addition to ASKAP, the new MeerKAT radio telescope in South Africa has also made many previously unseen discoveries in the Milky Way and the nearby Universe. Both are precursors to the supernova and the not yet fully built Square Kilometre Array radio telescope. So by 2030, discoveries in astronomy will be pouring in like a never-ending stream. All these and similar instruments are allowing radio astronomers to discover a new “Low Surface Brightness Universe” that would otherwise be invisible.

An example of the amazing work of radio astronomers is the ghostly Kýklos ring (from the Greek κύκλος, meaning circle or ring) and the object WR16, surrounded by rare and unusual Wolf-Rayet stars. When large stars run out of fuel, they become unstable and enter one of the last stages of their life cycle, turning into Wolf-Rayet stars. They begin to pulse and expand, shedding their outer layers, which can form bright nebulae around the star.

In the case of WR16, the previous ejection cleared the space around the star, allowing the current ejection to spread symmetrically in all directions. The resulting sphere of stellar material looks like a circle.

Left Kýklos, right WR16

The image below, from left to right and clockwise, shows the supernova remnants of Stingray 1, Perun, Ancora, and Unicycle. When a star of a certain large mass runs out of fuel, it can no longer hold back gravity. The falling matter causes a final explosion, which scientists call a supernova. The expanding shock waves of the supernova suck material into the expanding sphere, forming beautiful circular structures.

Over time, the supernova remnant will become deformed by the drag of the surrounding environment. For example, if one side of the explosion expands into an interstellar cloud of gas and dust, we would see a flattened shape. So a nearly perfect circle in the universe is a special find. But they do exist. Shown below is Teleios, named after the Greek word Τελεɩοσ (perfect) because of its nearly perfect round shape. This unique object has never been observed at any wavelength, including visible light, demonstrating the incredible ability of the ASKAP radio telescope to discover new objects.

The perfect shape of the supernova envelope indicates that Teleios was relatively untouched by its environment. This allows us to draw conclusions about the original supernova explosion, providing insight into the very beginning of one of the most energetic events in the Universe.

On the other hand, objects are being discovered that allow us to discover something completely new about them. For example, a supernova remnant has been discovered, named Diprotodon after one of Australia’s most famous megafauna, which lived about 25,000 years ago. This supernova remnant is one of the largest objects in the sky. It is about six times larger than the Moon.

Diprotodon. The green circle shows previous observations, the yellow circle covers new ones.

The sensitivity of the ASKAP array allowed the object to be seen in all its glory. Further analysis revealed the history and physics of the object. The object’s inhomogeneous internal structure reveals itself when different parts of its expanding shell crash into the matter-rich interstellar medium.

Another object that may show how new radio telescope data can change the classification of previously discovered objects is Lagotis. The VdB-80 nebula has been observed before in the disk of our Milky Way galaxy. The light we see was emitted by stars close to the object and then reflected off a spherical cloud of gas and dust.

Lagos

ASKAP observations revealed a cloud of ionized hydrogen gas (known as an HII region) associated with the object. The star’s energy has caused the gaseous material to lose electrons. The HII region is aligned with the nebula’s shell, creating a bizarre spherical effect in space.

The ASKAP and MeerKAT radio telescopes also detect objects beyond the Milky Way. For example, “radio ring” galaxies. In visible light, this is an ordinary flat disk galaxy uniformly filled with stars, while in the radio range it looks like a ring whose core has disappeared somewhere. Scientists are not yet ready to say why this happens, waiting for new data on such objects.

On the left is the radio ring galaxy, on the right is the LMC-ORC

Finally, the LMC-ORC object is an Odd Radio Circle (ORC), a remarkable new class of objects with unusual origins. Visible only in radio wavelengths, they are perhaps the most mysterious of all. Their secret is still waiting to be discovered. And there are many such wonders.