489607186

489607186

Satellite Communications Under A Starry Sky

Photo by: FilippoBacci

FilippoBacci

Odd Radio Waves Coming From Outer Space

First, some background. A huge collaboration of astronomers is currently busy spending some hard-won cash to build the world’s largest radio telescope array, called the Square Kilometre Array.

August 20, 2020

I won’t award you any points for guessing how big it is – but it's a total area of one square kilometer, with the individual telescopes split between Australia and South Africa.

It’s a big telescope, and it’s taking a long time to build.

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654647222

High resolution, low noise picture by multi-panel stitching.

Photo by: Haitong Yu

Haitong Yu

In the meantime, astronomers are testing a lot of the necessary technologies with various much smaller arrays, such as the Australian Square Kilometre Array Pathfinder (ASKAP).

ASKAP tests technologies and gets some useful science done in the form of deep-space radio surveys. During one such survey, the Evolutionary Map of the Universe Pilot survey (yes, astronomers are fond of absurdly long names for instruments and programs), ASKAP found… circles.

Yup, circles.

Now circles in radio surveys aren’t exactly a surprise by themselves. The best way to generate radio emissions is by moving and wiggling charged particles around. One way to do that is by shooting those charged particles up and down a long wire, which is relatively easy with antenna on the surface of the Earth but somewhat more challenging in the middle of the universe. The other way, is moving charged particles around in a circle, which makes…circular radio waves.

All sorts of cool and exciting sources make circular-shaped radio emissions: leftovers from supernova explosions, planetary nebulae (the leftover remnants of stars like our sun), materials just hanging out nearby random stars, disks of gas that are just beginning to form planets around newborn stars, and galaxies in especially vigorous periods of star formation.

You know, the usual.

But the three radio circles recently found with ASKAP (plus a bonus circle discovered in archival data) don’t match any of the known circle-making phenomena in the universe. And what’s more, they aren’t associated with anything else in particular: no galaxy, no explosive event, nothing in any other wavelength of light.

So they get a new name: Odd Radio Circles, or OCRs.

The authors of the recent study put forth a few brave hypotheses to explain these OCRs. One of the challenges in studying OCRs is that since we don’t know how far away they are, we don’t know how big they are. They could be close but relatively small, or far away and appropriately massive.

They could be winds from still-hidden galaxies blowing bubbles of hot gas. Or they could be something closer, say, stars nearing the end of their lives, and blowing bubbles of hot gas. They could be jets of material that got warped into rings. Or they could be tricks of gravity, caused by some massive but unseen object bending the paths of background light.

But no explanation seems to fit. They don’t match up with any known physical process, and they don’t look like anything else we’ve seen before.

They’re just…odd.

Paul M. Sutter

Paul M. Sutter is an astrophysicist at Stony Brook University and the Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of How to Die in Space.

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