People 'n' Issues

Cape doc helps find cosmic ‘train wreck’

August 18th, 2015
In the southern Milky Way, a galaxy collision has been uncovered by an international team of astronomers, one of whom is Michelle Cluver from the University of the Western Cape. This is the closest such “collisional ring” galaxy system ever detected.

The team of astronomers, led by Prof. Quentin Parker at the University of Hong-Kong and Prof. Albert Zijlstra at the University of Manchester, includes Dr Michelle Cluver from the University of the Western Cape. Their peer-reviewed paper appeared today in the Monthly Notices of the Royal Astronomical Society publication and details the discovery and description of this galaxy “train wreck.” It has been dubbed “Kathryn’s wheel” both after the famous fireworks that the system resembles, but also after the wife of the paper’s second author.

Such cosmic fireworks are very rare and arise from “bulls-eye” collisions between two galaxies of similar mass. Shock waves from the collision compress previously dormant reservoirs of gas 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.

Kathryn’s Wheel was discovered during a wide-field optical survey of the Milky Way.  The survey had been looking for the remnants of dying stars in our Galaxy, and the authors were very surprised to also find this example of a cosmic “ring of fire”, only about 30 million light years from us. This makes it seven times closer than the previous nearest example, and forty times closer than the famous ‘Cartwheel’ example of such systems. The galaxy is located behind a dense star field and close to a very bright foreground star, which is likely why its true nature had not been noted before. In addition, this appears to be a relatively empty region of space, making the chances of such a collision at this location very low.

Professor Parker said, “Not only is this system visually stunning, but it is 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.”

Dr Cluver added: “Further detailed studies of this system will help us learn more about the physics of shocks under these conditions, which may apply to a range of different astrophysical phenomena. In particular we are interested in how energy is dissipated from shocks to star formation.”

Smaller galaxies are more common than large ones enabling the authors to revise upwards the estimated number of such curious but rare phenomena by a factor of ten. They also find that Kathryn’s Wheel is probably the nearest collisional ring.


Prof. Q.A.Parker, Dr D.J.Frew and Dr I.Bojicic (HKU)

Prof. Albert Zijlstra and Dr George Bendo (University if Manchester)

Dr. Milorad Stupar (University of Western Sydney/Macquarie University)

Dr Michelle Cluver  (University of the Western Cape)

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