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UGA Astronomers Discover “Hot Tip” on Evolution of the Milky Way

by Phillip Lee Williams



University of Georgia astronomers have discovered a startling absence of hot gas in a spiral galaxy first cataloged more than 225 years ago. The galaxy, NGC 1068, may offer insights into the evolution of our own spiral galaxy, the Milky Way, said Robin Shelton, who led the research.

“In many ways, the younger NGC 1068 is a window on our past,” she said, “and the process of heating gas in these galaxies is more complex than we had expected.”

NGC 1068 is 60 million light years from Earth and moving away at more than a thousand miles a second. It was first discovered in 1780.

The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, launched by NASA in 1999, has provided researchers new information on the mysterious spiral galaxy. FUSE, an 18-foot-tall, 3,000-pound satellite that orbits nearly 500 miles above the Earth, has four telescopes that can function as a single instrument and analyze light at wavelengths too short for the famed Hubble Space Telescope to see.

“In late 2001, FUSE observed NGC 1068 during five different sessions,” said Shelton. The observation focused on a location in the galaxy about the same distance as the Earth is from the center of the Milky Way.

Researchers studied emissions of the tracer-gas oxygen+5 to see how much hot gas is in the disk of NGC 1068. Oxygen+5 has five fewer electrons than normal oxygen – a state that only occurs at extremely high temperatures. “It functions as a tracer of hot gas,” said Shelton, “so examining oxygen+5 tells us a lot about how much hot gas is in these galaxies.”

The astronomers based their expectations about the amount of hot gas in the galaxy on comparisons with the Milky Way, but the results showed dramatically less gas than expected. There should be considerable hot gas in NGC 1068, especially since its center is a huge black hole. The energy released around it might be compared to millions of atomic bombs continuously exploding, Shelton said. Also, NGC 1068 has “starburst regions,” where enormous “bubbles” of hot gas are blown.

“We just didn’t find the oxygen+5 we expected, and we’re not sure of the cause,” said Shelton.

For more information, email Robin Shelton at


Research Communications, Office of the VP for Research, UGA
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