Do mysterious “radio circles” form during explosions of galaxies?

In the early 1960s, successfully identifying the optical analogue of the source radio powerful discovery of radio telescopes of that time and dubbed 3C 273, astronomers notice that it looks like star but what is it range the light is strongly redshifted. As part of cosmology the relativism of that time is already quite well developed, which would mean that it is on the billionslight years distance and that therefore it radiates to be visible from afar, quantitiesenergy amazing and almost unbelievable, because no ordinary star or even stellar explosion can physically explain it.

Several hypotheses exotic proposed to explain the existence of this source and others like it that radio astronomers will discover within the same decade. The conservative hypothesis suggested that they were indeed stars, but very massive and therefore with a significant redshift due to their field of view. gravityfamous prediction general theory of relativity since its opening Einstein. Then these stars would be close and their brightness then the inner would have nothing extraordinary.

Other researchers in the same decade when The Big Bang Theory quickly established after opening cosmic radiation in 1965, more daring and exploratory, like Igor Novikov and Yuval Neeman proposed the idea that what we already call quasars may be partsUniverse expansion of which during big Bang was postponed (speculation lagging nucleus). They will even go so far as to suggest that these cosmic phenomena are the other end of wormholes ejecting to matter which they took in the form black holes in another part of space or even in another universe.

We think we now know that quasars are active galactic nuclei containing huge black hole accreting agent, such as M87* now pictured by collaborators Event horizon telescope.

From quasars to ORCs

Since 2019, however, British-Australian astronomer Ray Norris and his colleagues have been very puzzled by the handful of objects they have detected usingAustralian Pathfinder Array of Square Kilometers (Askap), an Australian network of radio telescopes that served as the prototype for the long-awaited Array of square kilometers (SKA), a virtual giant radio telescope project with a collecting surface equivalent to one square kilometer, is underway and integrates several instruments.

Askap’s first unusual object was named ORC 1, ORC for ” weird radio circles “, which can be translated as ” weird radio circles “.

As their name implies, they appeared on the radio as rings, but nothing in the visible region was associated with them, which ruled out the hypothesis that they could be remnants. supernovae or planetary nebulae, which may also have this aspect. Also, it is unlikely that these are radio lobes associated with supermassive black hole jets because they are much more irregular.

The distance, and therefore the size of these circles, had not yet been determined at the outset. But that just changed and posting in Royal Astronomical Society Monthly Notices (MNRAS), which can be viewed free of charge at arXiv, starts to give some answers.

Astronomers mobilized South African radio telescope MeerKATalso the predecessor of SKA, to whom we are already indebted discoveriesto better observe resolution ORC 1. It then became possible to find a new radio source at the center of the radio circle, a source that could be associated with the galaxy. After all, the data now collected suggests that we are in the presence of a ring located a billion light-years from Earth. Milky Way and, accordingly, about a million light years in diameter.

Similar conclusions were drawn with MeerKAT, and now it seems that ORCs are giant bubbles from gas very hot, the contours of which seem brighter, because we can see in the sections a large thickness of the material containing electrons relativists, forming a plasma immersed in magnetic fields and radiating, respectively. The presence of magnetic fields is detected by the polarization of radio waves measured using MeerKAT. This type of radiation is called synchrotron because it is observed in these particle accelerators on Earth, is well known in the Milky Way, and also in space. crab nebula.

Bubbles appear in the center galaxies discovered, and therefore it seems clear and established that they were blown up by these galaxies as if they were the shock front of a quasi-spherical explosion.

An artist’s impression of the formation of one of the strange radio circles from an explosion in the central galaxy. It is believed that the bubble from the explosion took 1 billion years to grow to the size we know today. Radio circles are so large (millions of light-years in diameter) that they extend beyond their original galaxies. © Sam Moorfield/CSIRO

However, the nature of the explosion remains unclear. It may be an unpredictable and unobservable phenomenon when two supermassive black holes collide after the merger of two galaxies.

It can also be a sudden formation collapse the gravitational force of about a million stars in the galaxy, with the birth of these stars causing a sudden outburst of plasma leaving the galaxy.

We should know more with an additional resolution increase once SKA is fully operational.

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