Analyzing data from the W.M. Keck Observatory on Mauna Kea and other sources, an Italian-led team of astronomers have gleaned surprising new insight into a cluster of stars first discovered 40 years ago — insight that could help to further understanding of how the Milky Way formed.

The international team, led by Francesco Ferraro of the University of Bologna, studied data from the Keck Observatory’s Near Infrared Camera, the Advanced Camera for Surveys and Wide Field Camera aboard the Hubble Space Telescope, and the Multi-conjugate Adaptive Optics Demonstrator at the European Southern Telescope’s Very Large Telescope in Chile.

They found that the globular cluster known as Terzan 5, located 19,000 light-years away within the Milky Way’s Galactic Bulge, is composed of both ancient and young stars.

The findings were published this month in the Astrophysical Journal.

Previous studies in 2009 found that Terzan 5 had two subpopulations of stars with different chemical abundances.

The most recent study found that the two groups were formed roughly 7 billion years apart, suggesting that the star formation process in Terzan 5 was not continuous but rather defined by two distinct bursts of formation.

“This requires the Terzan 5 ancestor to have large amounts of gas for a second generation of stars and to be quite massive — at least 100 million times the mass of the sun,” said study co-author Davide Massari.

Current theories assume that vast clumps of gas and stars interacted to form the Galactic Bulge, merging and dissolving in the process.

“We think that some remnants of these gaseous clumps could remain relatively undisturbed and keep existing embedded within the galaxy,” Ferraro said. “Such galactic fossils allow astronomers to reconstruct an important piece of history of our Milky Way.”