Dubbed “Kathryn’s Wheel” after the famous firework it resembles and after the wife of the paper’s second author. Such systems are very rare and arise from “bulls-eye” collisions between 2 galaxies of similar mass. Shockwaves from the collision compress reservoirs of gas in each galaxy and trigger the formation of new stars. This creates a spectacular ring of intense emission, and lights up the system like a Catherine wheel firework on bonfire night.
Galaxies grow through collisions but it is rare to catch one in the process, and extremely rare to see a bull’s-eye collision in progress. Fewer than 20 systems with complete rings are known. This occurred in the constellation of Ara (the Altar).
Kathryn’s Wheel was discovered during a special wide field survey of the Southern Milky Way undertaken with the UK Schmidt Telescope in Australia. It used a narrow wavelength optical region centred on the so-called red “H-alpha” emission line of gaseous hydrogen, uncovered during a search of the survey images for the remnants of dying stars in our Milky Way.
The newly discovered ring galaxy is 7X closer than anything similar found before, and 40X closer than the famous ‘Cartwheel’ galaxy. The ring is located behind a dense star field and close to a very bright foreground star, which is why it had not been noted before. There are very few other galaxies in its neighbourhood; the odds of a collision in such an empty region of space are very low.
Professor Parker said “Not only is this system visually stunning, but it’s close enough to be an ideal target for detailed study. The ring is also quite low in mass, less than 1% of the Milky Way – so our discovery shows that collision rings can form around much smaller galaxies than we thought.” Smaller galaxies are more common than large ones, implying that collisional rings could be 10X as common as previously thought. http://www.ras.org.uk/news-and-press/2699-celestial-firework-marks-nearest-galaxy-collision
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