Tau.Neutrino said:
Astronomers Detect Unexpected Class of Mysterious Circular Objects in Space
Although we usually have a pretty good handle on all the different kinds of blips and blobs detected by our telescopes, it would be unwise to assume we’ve seen everything there is to see out there in the big, wide Universe. Case in point: a new kind of signal spotted by radio telescopes, which has astronomers scratching their heads.
more…
> Western Sydney University in Australia has nicknamed them ORCs – short for “Odd Radio Circles” – in a new paper posted to arXiv and submitted to Nature Astronomy, where it awaits peer review. Circular features are well-known in radio astronomical images, and usually represent a spherical object such as a supernova remnant, a planetary nebula, a circumstellar shell, or a face-on disc such as a protoplanetary disc or a star-forming galaxy. The fourth ORC was discovered – in archival data, collected in 2013 with the Giant MetreWave Radio Telescope, a few years before ASKAP was switched on. Follow-up observations of ORC 1 and ORC 2 using a different telescope, the Australia Telescope Compact Array, also revealed the objects.
> late 2019 Pilot Survey of the Evolutionary Map of the Universe (EMU) conducted using the Australian Square Kilometre Array Pathfinder
Good on you ASKAP and ATCA.
> All four are also only visible in radio wavelengths – they are completely invisible in X-ray, optical, or infrared wavelengths. For planetary nebulae, the radio spectral index is not consistent with the radio spectral index of the ORCs. As for supernova remnants, the problem is with numbers. The EMU survey only looked at a small patch of the sky, and detected three ORCs. For that to be likely, there would need to be at least 50,000 supernova remnants in the Milky Way. We know of only around 350. The team believes that whatever is causing the ORCs is likely outside the Milky Way, like a giant spherical shockwave from some massive event.
Small for inside the Milky Way, Large for outside. If outside, quasar jets would be my guess.
> the jets of a radio galaxy or blazar when seen end-on, down the ‘barrel’ of the jet. Alternatively, they may represent some remnant of a previous outflow from a radio galaxy.
Oh, good, that’s what I just said.