Astronomers Have Determined That Two Satellite Galaxies Of The Milky Way Have Recently Collided

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For those who are in the Southern Hemisphere, there are two distant patches of milky clouds that can be seen in the night sky. These are both satellite galaxies of the Milky Way, known as the Small Magellanic Cloud and the Large Magellanic Cloud — and astronomers have determined that these galaxies have very recently collided with each other.

As reports, astronomers at the University of Michigan have just published a new study using data collected from the Gaia space telescope — which the European Space Agency launched — and have found that the “wing,” or southeast area of the Small Magellanic Cloud, is slowly drifting away from the larger part of the galaxy’s body.

Sally Oey, a University of Michigan professor of astronomy — and lead author of the new study — explained that you can now see clearly that the “wing” is detaching itself from the body of the Small Magellanic Cloud.

“This is really one of our exciting results. You can actually see that the Wing is its own separate region that’s moving away from the rest of the SMC.”

This discovery of the collision of the Milky Way’s satellite galaxies came about after Oey and undergraduate researcher Johnny Dorigo Jones were observing the Small Magellanic Cloud, searching for what are known as runaway stars. By using the Gaia space telescope, astronomers can easily trace the movement of stars across the sky, according to Oey.

“We’ve been looking at very massive, hot young stars — the hottest, most luminous stars, which are fairly rare. The beauty of the Small Magellanic Cloud and the Large Magellanic Cloud is that they’re their own galaxies, so we’re looking at all of the massive stars in a single galaxy.”

As Jones noted, “It’s really interesting that Gaia obtained the proper motions of these stars. These motions contain everything we’re looking at. For example, if we observe someone walking in the cabin of an airplane in flight, the motion we see contains that of the plane, as well as the much slower motion of the person walking. So we removed the bulk motion of the entire SMC in order to learn more about the velocities of individual stars. We’re interested in the velocity of individual stars because we’re trying to understand the physical processes occurring within the cloud.”

When Oey and Jones were analyzing the data from Gaia, they noticed that every one of the stars in the “wing” of the Small Magellanic Cloud were all cruising quickly at exactly the same speed. Said stars were also travelling in the same direction. What this demonstrated is that the Large and Small Magellanic Clouds had obviously collided with each other relatively recently, although in this case the term recently technically means something like a few hundred million years ago.

The new study, which demonstrates that two satellite galaxies of the Milky Way have collided, has been published in Astrophysical Journal Letters and can be read on arXiv.