It's not common for space to throw something completely new at us, but in 2019, astronomers discovered a completely unknown phenomenon they called the Singular Radio Circle (ORCS). Now, more data may shed light on how these rare objects formed.
Image of the Odd Radio Circle (ORC). Radio images captured by the Meerkat radio telescope are highlighted in green, while the background is filled with optical and near-infrared data from the dark energy survey english (u. manitoba)/emu/meerkat/des(ctio)
Everything you need to know about ORC is in the name: they are round radio emission clusters, and they are strange because the reason for their formation is unknown. The first few objects were discovered in data from the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope, and at first it was unclear whether they were small objects within the Milky Way or huge objects further afield.
ORCs are very faint and invisible to both infrared and optical wavelengths, making them difficult to study, but more information that emerged in 2022 is beginning to help determine their identity. The latter scenario was confirmed to be true – the ORC is enormous, millions of light-years wide, and is centered on certain galaxies. As it turns out, this can be the key to understanding them. In this new study, astronomers have uncovered an almost literal ironclad case for orc with:"starburst"The galaxies are connected.
Alison Coil, first author of the study, said:"These galaxies are very interesting. They appear when two large galaxies collide. The merger pushes all the gas into a very small area, which causes a violent burst of star formation. Massive stars burn up quickly, and when they die, they emit gas in the form of outflow winds. "
Of course, the birth of stars coincides with the death of stars, so these galaxies will have a large number of supernovae at the same time after a period of time. With a large number of stars nearby** at the same time, the gas they spew is accelerated into wind and flows out of the galaxy at a speed of 2,000 kilometers (1,240 miles) per second. The team suspects that ORC may be a later stage in the process.
To find out, they used optical and infrared light to look at galaxies located at the center of an ORC. Sure enough, there seemed to be a large amount of bright, red-hot compressed gas in the center there. Based on this data, they determined that the stars in the galaxy were about 6 billion years old, and that the period of crazy stellar explosions ended about 1 billion years ago.
Next, the team conducted simulations that calculated the properties of the galaxy, its stars, and the ORC around it. The results showed that the outflow blew for about 200 million years and then stopped. After that, a shock wave ripples out, pushing the hotter gas farther away, forming a radio circle, while another shock wave moves in the opposite direction, pushing the cooler gas back into the galaxy. The whole process takes about 7500 million years, which the team says is consistent with their initial estimate of the age of the structure.
A simulated image of how the exophoresis winds of a starburst galaxy form a singular radio sphere. MYR = million years. The upper part shows the gas temperature, and the lower part shows the radial velocity.
Cole said"To achieve this, you need a high-quality outflow rate, which means it can eject large amounts of material quickly. The density of the surrounding gas outside the Milky Way must be low, otherwise the shock will stall. These are two key factors. It turns out that the galaxies we've been studying all have this high mass outflow rate. They are rare, but they do exist. I really think this suggests that the ORC is derived from some kind of exogalactic wind. "
In this way, these radiospheres may no longer seem so strange. But the team says we still have a lot to learn about them, and they can teach us about galaxies in general.
Cole said"They can also help us learn more about the evolution of galaxies: do all massive galaxies go through an ORC phase?When spiral galaxies no longer form stars, do they become elliptical galaxies?I think we can learn a lot about ORC from ORC. At the same time, we are excitedly awaiting the next cosmic puzzle to emerge from the depths of space. "
The study was published in the journal Nature.