We have our best look yet at mysterious ORCs (individual radio circuits) in space

Astronomers have been puzzled over the nature and origin of the mysterious, rare radio circuits in space since the objects were first discovered in 2019. Now, the high-resolution MeerKAT radio telescope in South Africa has captured one of these circuits in much greater detail, providing some useful clues about this rare phenomenon. . The image and accompanying analysis appeared in a preliminary version on arXivAnd the the paper It has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

The discovery originated from Evolutionary map of the universe (EMU) which aims Takes enumeration radio sources in the sky. Several years ago, Ray Norris, an astronomer at Western Sydney University and CSIRO In Australia, the European Monetary Union project will bring unexpected discoveries. They were called “WTFs”. Norris admitted in piece 2020 For The Conversation, expect these discoveries to arise from machine learning analysis, given the massive amounts of data involved. He wrote, “But these discoveries were made by good old technique,”

One pair of eyeballs belongs to Anna Kabinska, an astronomer at the National Radio Astronomy Observatory (NRAO). While browsing through new radio astronomy data collected by CSIRO’s Australian Square Kilometer Array (ASKAP) telescope, Kapinska noticed several strange shapes that did not appear to resemble any known type of object. After naming Norris, she called them possible WTFs. One of these, Per Norris, “was an image of a ghostly circle of radio emission, suspended in space like a cosmic smoke ring.”

Soon, other team members found two strange circular points, which they called individual radio circuits (ORCs). A fourth ORC was identified in archival data from Giant MetreWave Radio Telescope, and a fifth was discovered last year in new ASKAP data. There are many objects that may also be ORCs. Based on this, the team estimates that there could be up to 1,000 ORCs in total.

while Norris et al. Initially assuming that the points were just artifacts, data from other radio telescopes confirmed that they were in fact a new class of astronomical objects. It does not appear in standard optical telescopes, or in infrared and X-ray telescopes – only in the radio spectrum. Astronomers suspect that the radio emissions are caused by clouds of electrons. But this does not explain why ORCs do not appear at other wavelengths.

All ORCs confirmed so far have a galaxy in the center, suggesting that this may be an important factor in how they formed. It is massive, about a million light-years in diameter, and larger than our Milky Way galaxy. “We know that ORCs are rings of faint radio emissions that surround a galaxy with a hyperactive black hole at its center, but we don’t yet know what causes them, or why they are so rare,” Norris said.

Astronomers have postulated several possibilities for what these objects might be. It might be a supernova remnant or Einstein’s rings. Alternatively, they may be caused by streams of electrons emitted from the vicinity of a supermassive black hole, although ORCs are more circular than the clouds typically seen resulting from this phenomenon in radio galaxies. The most speculated proposal assumed that ORCs might in fact be the “throats” of wormholes.

According to Norris, ASKAP is ideal for scanning large areas of the sky, while MeerKAT is designed to magnify any objects of interest, so the two telescope arrays are complementary. This latest radio image from MeerKAT shows several smaller rings within the larger outer circle. MeerKAT has also mapped the radio wave’s polarization, revealing a magnetic field along the edge of the sphere. This corresponds to an explosion in the center of the galaxy.

“We can now see that each of the ORCs is centered around a galaxy too weak to detect previously,” Norris wrote in his book. new article in conversation. “The circles are most likely massive explosions of hot gas, about a million light-years across, emanating from the central galaxy. From modeling the faint cloudy radio emission detected by MeerKAT within the rings, the rings appear to be the edges of a spherical shell around the galaxy, like a blast wave from a giant explosion.” In the galaxy. They look like rings rather than orbs just because the sphere appears brighter at the edges where there is more material along the line of sight, like a soap bubble.”

So what caused the explosion that led to the formation of ORCs? The new data is sufficient to rule out all but three possibilities. The first is that the ORCs are the result of a shock wave from the center of a galaxy, possibly arising from the merger of two supermassive black holes. Alternatively, it could be the result of radio jets spewing out particles from active galactic cores. Finally, ORCs may be projectiles generated by starburst events (“termination shock”), which would produce a spherical shock wave as hot gas ejected from the galactic center.

Determining which of these hypotheses is correct will require more data. A large group of radio telescopes, dubbed the Square Kilometer Array (SKA), are due to go online in 2028, and Norris is confident that SKA will find many more ORCs and hopefully reveal more details about the life cycle of galaxies. This additional observational data may also enable astronomers to identify the strange curved filaments of radio emissions lurking within the outer ring.

Meanwhile, many astronomers are enjoying having a new cosmic mystery to solve. “People often want to explain their observations and show that they are consistent with the best information we have,” Co-author Jordan Collier said: From the Interuniversity Institute for Data-Intensive Astronomy. “For me, it is even more exciting to discover something new that challenges our current understanding.”

DOI: Monthly Notices of the Royal Astronomical Society, 2022. 10.1093/manras/stac701 (About DOIs).