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Celestial firework marks nearest galaxy impact


An amazing galaxy collision has been detected lurking behind the Milky Way. The closest such system ever detected, the discovery was declared at 16 August 2015 by a team of astronomers directed by Prof. Albert Zijlstra at the University of Manchester and Prof. Quentin Parker at the University of Hong Kong. The researcher’s results were announced in Monthly Notices of the Royal Astronomical Society.
The galaxy is 30 million light years away, which indicates that it is relatively close by. It has been called “Kathryn’s Wheel” both after the well-known firework that it look like, and also after the spouse of the paper’s second writer.
Galaxies grow through collisions but it is sporadic to catch one in the process, and very rare to see a bull’s-eye collision in evolution. Less than 20 systems with full rings are identified.

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Color image of the collision, made by merging the CTIO H-alpha representation with blue and red images. For better clarity, the bright star to the south has been removed so as not to distract from the observable effects of the bull’s-eye collision. The H-alpha illustration was taken with a “narrow-band” filter sensitive to the great burst of star formation arising in the ring round the central elongated galaxy. The image measures about 4 arc minutes across and all were taken on the Cerro-Tololo Inter American Observatory (CTIO) 4-metre telescope in Chile. Image credit: Ivan Bojicic / the scientific team.

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Color image of the collision, made by merging the CTIO H-alpha photo with blue and red reflections in other colors. In this interpretation the bright star to the south has been left in place while the dynamic ring of star formation focused on the elongated galaxy at the center of the photo has been rendered a fiery orange. These images were taken on the Cerro-Tololo Inter American Observatory (CTIO) 4-metre telescope in Chile. Image credit: Ivan Bojicic / the scientific team.

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Residual image of the collision, created by subtracting the red image from the CTIO H-alpha photo, which mostly cancels the influences from regular stars and is effective in highlighting just the areas of active star creation. For clarity any remaining stellar residuals have been removed. The images were taken on the Cerro-Tololo Inter American Observatory (CTIO) 4-metre telescope in Chile. Image credit: Quentin Parker / the scientific team.
Professor Parker declared “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 — a few thousand million Suns, or less than 1% of the Milky Way — so our discovery shows that collision rings can form around much smaller galaxies than we thought.”
Professor Zijlstra supplementary said “It is not often that you get to name any objects in the sky. But I think Kathryn’s Wheel is particularly fitting, resembling as it does a firework and continuing the tradition of naming objects after loved ones.”

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