There’s an epic fight under way on the outskirts of the Milky Way

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  Last updated November 12, 2018 at 3:44 pm


It’s a David vs Goliath battle between two dwarf galaxies – and David is getting hammered.

The Magellanic Clouds have repeatedly interacted over the past billion years, majorly distorting both. Credit: Dougal Mackey, ANU

On the outer edge of the Milky Way there is a brutal fight going on between two dwarf galaxies, tearing chunks from each other and flinging them into the gaseous Magellanic Stream, like a cosmic river of blood encircling our galaxy.

Astronomers from the Australian National University have observed the violent stoush between the Large and Small Magellanic Clouds, located 150,000-200,000 light years away from Earth.

While the dwarf galaxies are visible at night with the naked eye from the southern hemisphere, researchers led by Dougal Mackey took a closer look, developing an ultra-faint map of stars in the outer edges of the Clouds using the Dark Energy Camera installed on the Blanco telescope in Chile. Their results have been published in Astrophysical Journal Letters.

With the Large Magellanic Cloud around twice the diameter of its smaller associate, it has been likened to the biblical tale of David vs Goliath. But unlike in the tale, Goliath is exerting its larger size.

“This fight is a lot like the one that David and Goliath could have had if the little guy didn’t have such good luck with his sling shot,” says Mackey. “The Large Magellanic Cloud is really beating up its smaller companion.”

Nearly 200 000 light-years from Earth, the Large Magellanic Cloud, a satellite galaxy of the Milky Way, floats in space, in a long and slow dance around our galaxy.
Credit: NASA/ESA Hubble Space Telescope.

A billion-year battle

The results show that over the last billion years there have been repeated interactions between the two clouds.

This has resulted in warping of the shape of both clouds, with the outer parts of the Small Cloud elongated towards and away from the Large Cloud. However, the Large Cloud has not escaped unscathed, with major distortions to its outer regions, including heavily warped regions nearest the small cloud.

Mackey says the results provide further evidence that the nasty and continuous conflicts between the two clouds have created the Magellanic Stream, a long trail of gas streaming from the Magellanic clouds.

Only visible at radio wavelengths, the stream extends around almost half of the Milky Way, passing beneath the south galactic pole and through both Magellanic clouds. Their observations also revealed young stars forming in the area of the stream between the clouds, called the Magellanic Bridge.

However, one of the most unexpected results was the discovery of a brand new tiny galaxy between the clouds. Named Hydrus I, it is one of a relatively recently discovered category of galaxies called ultra-faint dwarves. While being extremely low-brightness dwarf galaxies, they still have a large amount of dark matter.

“Hydrus I is likely to be a satellite of either cloud, or both, that has fallen into the Milky Way together with its larger companions,” says Mackey.

However, like Hydrus I, the clock may be ticking for the Magellanic clouds.

“The clouds will eventually be completely consumed by the Milky Way, but we would like to know how long they have left, and what sort of impact they will make before their ultimate destruction,” say the researchers.


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About the Author

Ben Lewis
Ben Lewis is the Editor of Australia’s Science Channel, and a contributor to Cosmos Magazine. He has worked with scientists and science storytellers including Jane Goodall, Dr Karl, Brian Cox, Chris Hadfield, Robert Llewellyn, astronauts, elite athletes, Antarctic explorers, chefs and comedians. Ben has also been involved in public events around Australia and was co-writer, producer and director of The Science of Doctor Who, which toured nationally in 2014 in association with BBC Worldwide Australia & New Zealand. Want more Ben? You can hear him on ABC and commercial radio in Adelaide, regional SA, across NSW, and the ACT. He also speaks at universities around Australia on communicating science to the public. Around the office he makes the worst jokes known to mankind.

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