Magellanic Cloud: Knots Of Evaporating Gas In Supernova Remnant Support Theory

"One theory concerning the global structure of the interstellar medium says that supernova shock waves will interact with the cold gas and dust of the interstellar medium, eventually forming three distinct temperature phases," said You-Hua Chu, a U. of I. professor of astronomy. "Although this 'three-phase model' has been popular for the past 20 years, no one had found convincing evidence for one of the model's basic tenets -- a cold cloud evaporating in the hot medium."

To study the supernova remnant -- called N63A, Chu and her colleagues obtained optical images from the Hubble Space Telescope and high-resolution X-ray images from the ROSAT X-ray telescope. "The X-ray observations reveal the full extent of this huge supernova remnant," Chu said, "but the optical images show the features we are most interested in."

Among those features are three bright clouds of gas and dust, similar in size to the Orion Nebula. Two of the clouds show distinct filamentary structures indicative of shock-wave compression, Chu said. The outward rushing shock wave has not yet reached the third, most distant cloud.

Numerous shocked cloudlets -- smaller clumps of gas embedded in the interstellar medium -- also were detected within the supernova remnant. "Swept back by high-velocity shock waves, these evaporating cloudlets provide clear support for the three-phase model," said Chu, who presented the team's findings at the American Astronomical Society meeting, held Jan. 5-9 in Austin, Texas.

After a massive star is formed, its stellar wind blows much of the surrounding interstellar medium away, creating a huge shell in space called an interstellar bubble. "Because the interstellar medium is not homogeneous, the denser knots of material [cloudlets] are left behind," Chu said. "The optical emission region of this supernova remnant appears the way it does because the supernova exploded inside an interstellar bubble in a cloudy medium."

The supernova remnant lies in the Large Magellanic Cloud, a small neighboring galaxy to our own Milky Way, about 160,000 light-years from Earth.

In addition to Chu, collaborators on the project included astronomer John Dickel, visiting researcher Adeline Caulet, and graduate students Sean Points and Rosa Williams (all at the U. of I.); astronomer Margarita Rosado and graduate student Lorena Arias-Montano at the Universidad Nacionale Autonoma de Mexico; astronomer Annie Laval and graduate student Patricia Ambrocio-Cruz at the Marseille Observatory; and astronomer Dominik Bomans at the University of Bochum in Germany.