Galaxies come in various forms and sizes, from giant spiral disks to ball-shaped blobs. Much of what we know about galaxies comes from optical images, which are either taken from backyard telescopes or space-based imaging tools. Recently, astronomers have used radio telescopes, which allow experts to map the glow of free-floating atoms throughout the universe, providing a glimpse of much more interesting happenings beyond the bright disk of stars.
Giant Eye in Space
In Wajarri Yamaji Country in Western Australia, astronomers discovered two rare polar ring galaxies that look like giant eyes with entire galaxies within. They were spotted during a study of hydrogen gas in 600 galaxies using CSIRO's Australian Square Kilometre Array Pathfinder (ASKAP).
The two galaxies, named, are spiral galaxies found in the constellations Virgo and Ara, respectively. They were seen as part of the WALLABY pilot survey, which aims to detect atomic hydrogen emission from around half a million galaxies.
NGC 4632 is among the first-ever galaxies discovered to have a polar ring by a radio telescope. Located at a region in space 56 million light-years away from Earth, this galaxy is circled by a huge ring of gas wrapping around the galaxy at a highly inclined angle to its galactic plane. It was not seen until now because it is invisible in most electromagnetic spectrums and appears only when the sky is observed with radio telescopes.
The astronomers are hopeful that further research could reveal more about the rare polar ring galaxies. They expect to reveal the type of ring, whether gaseous or star-filled, associated with the structure of the host galaxy.
What is a Polar Ring Galaxy?
Polar ring galaxies (PRGs) are unusual galaxies with beautiful gas rings perpendicular to a spiral disk of stars. They are best known for their ring composed of gas, dust, and stars, which orbit around or close to the galactic pole perpendicular to its plane.
Scientists still cannot explain how these rings formed, but two current leading theories exist. The first one is that materials traveling along the cosmic web through intergalactic space ended up orbiting around a galaxy and becoming part of it. The second, more commonly accepted theory is that the ring is composed of material gravitationally slurped from another galaxy that came close to and interacted with the polar ring galaxy.
According to Dr. Nathan Deg from the Department of Physics, Engineering Physics, and Astronomy at Queen's University in Canada, the discovery of NGC 4632 and NGC 6256 reveals that 1%-3% of nearby galaxies could have gaseous polar rings, more than what is suggested by optical telescopes. His colleague, Dr. Kristine Spekkens, also indicates that the results of their investigations illustrate the important value of mapping the sky more widely and deeply than ever.
It was observed that polar rings are more common in galaxies of the elliptical and lenticular types. Such galaxy types are unstructured and fuzzy, and do not have well-defined spiral arms seen in galaxies like the Milky Way. Experts are hoping that by exploring PRGs, they can gain a better understanding of the evolution of galaxies.
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