How many secrets of the universe remain unsolved?

One day in 2019, Anna Kandinsky of the University of Western Sydney's Faculty of Science was observing the Australian Square Kilometer Array Pathfinder (ASKAP) when she suddenly spotted a very mysterious object. As a female scientist, she couldn't help but say, "WTF!"

The Square Kilometer Array is one of the most powerful observing devices in the world today, and it was with this observing capability that it discovered this strange object. In the image, this kind of object is like a mysterious cloud of smoke in the universe, floating in interstellar space.

This mysterious object, which they jokingly called WTFs, however, also came up with a professional term - Odd Radio Circles (ORCs).

As the name implies, this mysterious object is invisible in the visible band and can only be observed using radio telescopes. In images taken by telescopes, they appear as circles, which are relatively brighter around and fainter inside when observed at radio wavelengths.

A circular object is the most common in the universe, but it is different from all known objects. And, since our knowledge of it is almost nil, scientists do not know exactly how far away they are from us. The inability to determine the distance makes it impossible to determine how large the odd radio circles are, which makes it even more difficult for scientists to determine their nature.

The earliest exotic radio circles were photographed by ASKAP in 2019 when a total of three were discovered. Two of them were confirmed when observations were made using other telescope arrays. Subsequently, other telescopes also reported new data. With these four data, astronomers determined that the phenomenon was not a problem with the telescope itself.

That being the case, could it be some special phenomenon of a known celestial body?

Scientists have proposed many speculations, such as supernova explosion relics, charged particles ejected by supermassive black holes, Einstein rings from gravitational lending effects, or radio rings of galaxies, etc., but in the end, all these candidate answers were ruled out. It seems that it is indeed a new kind of object that we have never seen before.

So, what is the nature of this strange radio ring? Only by finding more objects like them will scientists have a chance to understand them better.

To this end, Barbel Korzybski, an astronomer from CSIRO and the University of Western Sydney, led a scientific team that used ASKAP to make a large number of observations during December 2019-2020, and indeed found some new exotic radio circles.

Notably, at the center of one of these strange radio circles, the team found an elliptical radio galaxy. This galaxy, in turn, is located almost exactly in the center of the strange radio circle.

They suddenly realized that two of the four circles found in previous studies also had elliptical radio galaxies at their centers. The team pointed out that statistically speaking, the probability that the center of an exotic radio circle coincides with another radio source and is observed by us is one in a few hundred. Now, we have found three in one breath.

This means that the probability of a coincidence between them is almost non-existent and that there must be some unknown connection between these strange radio circles and the inner radio galaxies. Accordingly, the research team came up with three more possible conjectures.

Radio flaps

In general, in radio galaxies, there is usually a radio flap, a huge elliptical radio flap that spreads out on both sides of the galactic nucleus and is only observable in the radio band. There is a possibility that we happen to be observing directly across from this radio flap, so the shape we see is a circle-shaped strange radio ring.

Galactic center explosion waves

We know that the center of galaxies is usually the most chaotic and bizarre region of the whole galaxy. Therefore, the strange radio circles could also be coming from some kind of huge explosion inside the galactic nucleus. However, given the size of the strange radio ring, the source of such an explosion would need to be very, very large, such as a collision of two supermassive black holes.

Interaction of galaxies with the medium

There is also the possibility of an interaction between radio galaxies and the intergalactic medium. However, the team believes that this is not very likely and that the first two speculations are more likely to be the real situation.

In any case, now that the relationship between the strange radio circles and the inner radio galaxies has been found to exist, we can at least determine their distances and sizes. If, for example, an elliptical radio galaxy named EDS J010224.33-245039.5 is indeed related to one of them, then the size of this strange radio circle should be 980,000 light years.

This is also quite important data for astronomers. Whether it comes from a radio flap or an explosion wave, this size can help us understand the scale data of their occurrence.

For now, astronomers have discovered only a very limited number of strange radio circles, so many questions remain open. Although this study is an important contribution to our understanding of such objects, more observations and studies are needed if we want to figure out the secrets of the strange radio circles.

As astronomers discover more and more strange radio circles, we can find more commonalities, and these commonalities are an important means for us to understand the mechanism of their production.

As human observation capabilities improve, we are bound to discover more and more mysterious objects. It is hard to imagine how many secrets of the universe have yet to be discovered.