What we thought was a fairly ordinary spiral galaxy not far from the Milky Way has revealed a hidden surprise. About 56 million light-years away, NGC 4632 orbits the galaxy surrounded by a massive ring of gas that rotates at a high angle to the galactic plane. Why haven’t we seen this before? It is invisible in most of the electromagnetic spectrum, appearing only when we look at the sky through radio telescopes.

This finding could place NGC 4632 in the extremely rare class of galaxies known as polar ring galaxies, but it also suggests that these galaxies may not be as rare as we think. On the contrary, NGC 4632 may mean that we are looking at them from the wrong angle.

“The data suggest that one to three percent of nearby galaxies may have gaseous polar rings, much more than optical telescopes suggest. Galaxies with polar rings may be more common than previously thought,” says astrophysicist Nathan Dague of Queen’s University in Canada.

“Although this is not the first time astronomers have observed polar ring galaxies, NGC 4632 is the first galaxy observed with ASKAP, and many more may follow.”

Galaxies with polar rings are what they sound like: galaxies with a ring of material consisting of dust, gas, and stars orbiting at or near the galactic poles; that is, perpendicular to the galactic plane. They usually look quite impressive; its bright rings are curved like the donut of the von Braun space station.

We don’t know how they reached this conclusion, but there are currently two leading competitors. The first is that the material travels through the cosmic web of intergalactic space and falls into orbit around the galaxy, forming part of it.

A second and more common explanation is that the ring consists of material gravitationally collected from another galaxy that approaches and interacts with the polar ring galaxy. Interestingly, these are, as a rule, galaxies of lenticular and elliptical types with polar rings. These are fuzzy, unstructured galaxies that do not have the distinctive spiral arms seen in galaxies such as the Milky Way.

Optical observations have revealed polar rings in about 0.5 percent of the nearest lenticular galaxies. But there is much more to the universe than what our limited human eyes see. However, Daeg and an international team of astronomers did not necessarily expect a hidden polar ring to exist around spiral galaxy NGC 4632.

It was revealed in data collected by the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY) operated by the Australian Square Kilometer Array Pathfinder, a powerful radio telescope array located in the Western Australian desert. WALLABY’s goal is to survey hundreds of thousands of galaxies in the southern sky and map the gas distribution within them.

“NGC 4632 is one of only two galaxies with polar rings that we identified from the 600 galaxies mapped in our first small WALLABY survey,” says astronomer Berbel Korybalski of the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia.

“We expect to discover more than 200,000 hydrogen-rich galaxies using ASKAP over the next few years, including many more unusual galaxies such as polar rings.” Source