Astronomers using the W.M. Keck Observatory on Mauna Kea have been studying a "dwarf galaxy" about 2.6 million light years from Earth to try to get a picture of what our own Milky Way galaxy might have looked like billions of years ago.

The study of the very faint IC 10 galaxy also used images from NASA's Hubble Space Telescope, and has revealed evidence of a vigorous star formation event that took place within the last 10 million years.

That research is giving astronomers a picture of what the Milky Way might have looked like billions of years ago before the galaxy's interstellar medium was enriched with elements such as oxygen and nitrogen.

New images of IC 10 reveal a small region of space teeming with nearly a thousand stars, and astronomers suspect they may detect still more.

Astronomers have known that IC 10 has more giant, rare stars called "Wolf-Rayet stars" than all other nearby dwarf galaxies combined. Wolf-Rayet stars are extremely hot blue stars losing enormous amounts of mass to the interstellar medium.

Those stars present a puzzle because in that kind of collection of stars containing carbon, astronomers also expected to see a number containing nitrogen. Instead, very few nitrogen stars have been found.

Now that the Hubble and Keck telescope images have revealed many previously undiscovered stars in IC 10, each new star can be studied to determine its chemical composition. If the newly found stars contain nitrogen, then part of the "missing nitrogen" puzzle might be solved.

Dr. William Vacca at the NASA Ames Research Center led the study, and said IC 10 may answer many unresolved questions about stellar evolution.

"IC 10 is a remarkable galaxy," he said. "It is the only one we've seen that falls outside an established pattern of having a certain number of massive nitrogen-type stars for each carbon-type star. This imbalance has caused us to wonder if our past conclusions about massive stars have been correct. Do we need to revise the models of stellar evolution?"

The new images of IC 10 are centered on a bright star first thought to possibly be the most luminous Wolf-Rayet star in IC 10. Follow-up studies then found the star to be comprised of at least three or more components. Now, new data from Keck show the bright star, known as [MAC92] 24, is actually six or more stars, perhaps even a cluster of stars.

"The combination of HST images in the optical and Keck Laser Guide Star images in the infrared has been a major breakthrough in our understanding of dense stellar regions," said co-author Dr. James R. Graham, a professor of astronomy at the University of California-Berkeley.

"IC 10 has so many stars in such a tiny region of space that ground-based studies have been confused. But the combination of HST and Keck has been revolutionary in our understanding of this object, and for any object with a dense region of stars."

Though the properties of stars is one of the most well-studied topics in astronomy, scientists still don't fully understand all the mechanisms involved in star formation and evolution, particularly in galaxies with low levels of oxygen, nitrogen and other heavy elements.

Scientists studying the IC 10 galaxy may soon understand how stars might have looked in the distant past, when the universe was in a younger, more pristine form.

"A few years ago these types of studies would have been impossible from the ground," said Dr. Taft Armandroff, director of the Keck Observatory, who has studied dwarf galaxies. "We can now study individual stars of galaxies several million light years from Earth to understand how star formation events may have affected the evolution of the Milky Way galaxy. This galaxy can teach us what the most common types of galaxies in the universe might be like."

The findings were published in the paper called "Imaging of the Stellar Population of IC 10 with Laser Guide Star Adaptive Optics and the Hubble Space Telescope," in the June 10 issue of Astrophysical Journal.

The research was financed by grants provided by the National Science Foundation and the National Aeronautics and Space Administration.