Astronomers witness David versus Goliath fight between galaxies

November 8, 2018 by Will Wright, Australian National University
The research team developed this map that reveals the Magellanic Clouds have had repeated interactions with each other over billions of years. Credit: Dougal Mackey, ANU

Astronomers have witnessed, in the finest detail yet, a brutal David-vs-Goliath fight between two nearby galaxies that are tearing chunks from each other and flinging them into the gaseous Magellanic Stream, a cosmic river of blood encircling our Milky Way.

The new study led by ANU investigated the violent stoush between the Large and Small Magellanic Clouds—dwarf galaxies on the Milky Way's periphery that are visible at night with the naked eye from the southern hemisphere.

Lead researcher Dr. Dougal Mackey from ANU said the team created an ultra-faint map of stars in the outer edges of the Clouds using the Dark Energy Camera on the 4m Blanco telescope in Chile and revealed the Clouds have had repeated interactions with each other over billions of years.

"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," said Dr. Mackey from the Research School of Astronomy and Astrophysics at ANU.

"The Large Magellanic Cloud is really beating up its smaller companion—the outer parts of the Small Cloud are strongly elongated both towards and away from the Large Cloud."

The distribution of stars with different ages in the Small Cloud indicates possible unpleasant encounters with the Large Cloud stretching back several billion years.

"The Large Cloud has definitely not come away unscathed from these brawls, as the side closest to the Small Magellanic Cloud is heavily warped and pruned, and other parts of its outskirts show major distortions."

Dr. Mackey said the results provided further evidence that the nasty and continuous conflicts between the two Clouds had created the Magellanic Stream.

"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," he said.

"We also revealed, in the best detail so far, young stars forming in Magellanic Stream between the Clouds—this part of the Stream is known as the Magellanic Bridge."

Dr. Mackey said the team also discovered a previously unknown tiny galaxy, called Hydrus I, sitting in between the two Clouds.

"This galaxy is part of a class known as ultra-faint dwarfs, the existence of which was only discovered about 10 years ago. These are extremely low-brightness dwarf galaxies, but they still have lots of dark matter," he said.

There is broad scientific consensus that dark matter—matter that scientists cannot see—is widely present in the Universe and helps explain how hold together rather than fly apart as they spin.

"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," Dr. Mackey said.

Astronomers from the United Kingdom and United States supported the study, which is published in the Astrophysical Journal Letters.

Explore further: Magellanic clouds duo may have been a trio

More information: Dougal Mackey et al. Substructures and Tidal Distortions in the Magellanic Stellar Periphery, The Astrophysical Journal (2018). DOI: 10.3847/2041-8213/aac175

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Joe1963
1 / 5 (10) Nov 08, 2018
Gravity reverses and becomes repulsive at approximately 1.5 million light years. It becomes more and more strongly repulsive, reaches a peak, and then decreases trailing off to zero.

This does away both with dark matter and also dark energy.

It also explains gravitational rotational rates without the need of dark matter. Galaxies are pushing dust and gas into the interstitial space between galaxies. This dust and gas means that each galaxy or small galaxy cluster is surrounded by a womb of material at a distance that repulsive gravity operates. This repulsive womb, along with the pressure from other galaxies, holds outer stars in place, explaining higher than expected rotation.
You may read the justification for this theory here, along with responses to objections at the bottom:
https://www.reddi...tter_is/
Surveillance_Egg_Unit
1.7 / 5 (7) Nov 09, 2018
@Joe1963

Just wondering why someone gave you a "1" rating instead of a "5".
Oh wait - it surely must be that old bugaboo "DARK MATTER" and its kid brother, Dark Energy that most scientists and physorg 5-Star Club members cling to and cry over if anyone DARES to insinuate that DM doesn't and never did exist. They can't SEE it, but their faith in it never falters.
I'm not too sure about "repulsive gravity" though. It seems too much of an oxymoron to me.
Old_C_Code
5 / 5 (7) Nov 09, 2018
Joe1963: that is not only wrong, but literally insane. 1.5m light years is to the edge of Andromeda galaxy our nearest neighbor. To say gravity reverses or is zero in the rest of the universe is truly, insane.
jonesdave
5 / 5 (5) Nov 09, 2018
Gravity reverses and becomes repulsive at approximately 1.5 million light years. It becomes more and more strongly repulsive, reaches a peak, and then decreases trailing off to zero.

This does away both with dark matter and also dark energy.

It also explains gravitational rotational rates without the need of dark matter. Galaxies are pushing dust and gas into the interstitial space between galaxies. This dust and gas means that each galaxy or small galaxy cluster is surrounded by a womb of material at a distance that repulsive gravity operates. This repulsive womb, along with the pressure from other galaxies, holds outer stars in place, explaining higher than expected rotation.
You may read the justification for this theory here, along with responses to objections at the bottom:
https://www.reddi...tter_is/


Utter idiocy.
tblakely1357
not rated yet Nov 09, 2018
"Gravity reverses and becomes repulsive at approximately 1.5 million light years. It becomes more and more strongly repulsive, reaches a peak, and then decreases trailing off to zero.

This does away both with dark matter and also dark energy."

While I think dark energy and dark matter are a kludge similar to the luminiferous aether in the late 1800s, the above is just as kludgey and makes even less sense.
tgmeloche
1 / 5 (1) Nov 09, 2018
Evidence dark matter research is a waste of public money!
Parsec
not rated yet 14 hours ago
@tg - what on earth does this article have to do with dark matter? First rule of posting... post first THEN smoke crack. Reversing the order makes you look like an idiot.
rrwillsj
not rated yet 4 hours ago
As I've pointed before. The gaggle of stupid fulminating against the phenomena called "Dark Matter" "Dark Energy" and "Black Holes"?
Are basically asserting their innate racist bigotry.

Those words "dark and black" scare them into a hysteric rage,

If only there had been a little more care taken by the original authors in choosing those designations? I doubt if all this woomongering controversy would would be as extent.

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