Two Iowa State physics and astronomy professors, Dr. Phil Appleton and Dr. Curt Struck, have their heads in the clouds. High speed, galactic “comet clouds,” that is.

With the help of the Hubble Space Telescope (HST), the two professors, along with a team of scientists, have discovered “supersonic” gas clouds in the heart of the Cartwheel galaxy about 500 million light years from earth. The clouds may give astrophysicists a clearer idea of the conditions leading to star formation in galaxies.

“What we are seeing is sort of the late stages of the effects of [galaxy] collisions,” Appleton said.

“We are trying to understand how galaxies formed in the early universe. Ultimately we are trying to understand how the Milky Way came about.”

The Cartwheel galaxy was formed during a recent collision with another galaxy, a phenomenon which lead to its wheel-like shape. During such collisions a great deal of matter is “splattered” out into space, Appleton said.

Eventually clouds of gas and dust fall back toward the center of the target galaxy, at great velocity due to the force of gravity, where they collide with more gas and dust left over from the galactic collision.

Because of their v-shaped, comet-like structures scientists think the clouds are made up of dense material possibly moving as fast as a thousand times the speed of sound, he said.

The processes that create them may be similar to those that create the shock waves in front of supersonic aircraft.

“We are inferring from the shapes of these arrowhead structures that we are dealing with a supersonic collision of some sort,” Appleton said. “Its very hard to think of other explanations for what would explain these structures.”

Galactic collisions, like the one that created the Cartwheel, cause the formation of some of the most massive stars known in the universe, Appleton said.

“This is a very special kind of galaxy collision that gives us more evidence in the evolution of galaxies and star formation,” said Struck, in a press release.

“When a galaxy gets a kick from a collision, that speeds things up, triggering the formation of more stars. This discovery gives us insight into why this type of collision produces a different result.”

“In a sense we are seeing the smoking gun that galaxies really do collide,” Appleton said. “It’s exciting from that point of view. Before it has always been kind of speculative.”