Aug 08, 2016 I Paul Seaburn

Deadly Cloud Blasts a Huge Hole in the Milky Way

The only thing more puzzling than unidentified objects is a complete void of objects in an area where there's supposed to be something … anything. So astronomers were understandably puzzled when they scanned our Milky Way galaxy that is normally dense with stars, dust, gases and other stellar stuff and found patches (if you can call a void that’s 3,000 light year across a ‘patch’) of nothingness. For the first time, the cause of one of these voids has been identified and it’s a high-velocity cloud. A what?

South Korean astronomers Geumsook Park and Bon-Chul Koo report in Astrophysical Journal Letters about their study of a rare phenomena known as supershells or the more friendly "superbubbles." These are huge (2,000 light years or more wide) dense clouds of dust formed by stellar explosions from multiple clustered supernovas. The gas released expands like a bubble or balloon, pushing everything else out of its way and leaving a super-sized supershell to fill the space. Well, that’s what happens everywhere but in the Milky Way.

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An illustration of a Milky Way supershell

There are 20 supershells in the Milky Way and nearby galaxies that have no evidence of a cataclysmic event in their centers. Park and Koo took a new look at one of them and found a surprising cause – another type of high-velocity denser cloud blasted through the Milky Way and carved a hole that became a supershell. What kind of cloud has that kind of power?

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The Smith Cloud, another high-density cloud

This one has a name. HVC 040+01-282 (for its coordinates near the Scutum-Centaurus arm of the galaxy) is better known as CHVC040 (the C stands for compact, not crusher). It’s one of about 300 known high-velocity clouds in the Milky Way that travel around with tails that make them look like gassy comets ... deadly gassy comets whose cause is unknown but are most likely formed by exploding galaxies or supernovas. What happens when one of them runs into something of substance?

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Illustration of a high-velocity cloud heading towards a collision with the Milky Way

Park and Koo were studying CHVC040 when they noticed that there was nothing around it for thousands of light years. When they finally reached the edge of nothingness, they determined it was in the center of a supershell and was probably the cause of it. Looking at the data, they determined that indeed there was no other possible cause for this hole than a collision between a high-velocity cloud and a piece of the galaxy, making this the first known supershell caused by a rogue high velocity cloud.

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Top: The supershell. Bottom: At the center is the high-velocity cloud,Geumsook Park and Bon-Chul Koo / Seoul National University

The astronomers are quick to point out that these destructive clouds and the voids they create are a good thing. Supershells act as galactic chimneys that heat up heavy elements and create new gases that can form new stars. They also note that there are at least 300 known high-velocity clouds plowing their way through the Milky Way which are probably responsible for creating many giant galactic holes and will likely blast more in the future.

Great. Something else to keep us awake at night beside the election.

Paul Seaburn
Paul Seaburn is the editor at Mysterious Universe and its most prolific writer. He’s written for TV shows such as "The Tonight Show", "Politically Incorrect" and an award-winning children’s program. He's been published in “The New York Times" and "Huffington Post” and has co-authored numerous collections of trivia, puzzles and humor. His “What in the World!” podcast is a fun look at the latest weird and paranormal news, strange sports stories and odd trivia. Paul likes to add a bit of humor to each MU post he crafts. After all, the mysterious doesn't always have to be serious.

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