Terzan 5, a globular cluster that wasn't much thought of since it was first discovered some 40 years ago, has recently received a second look by astronomers at the European Southern Observatory's Very Large Telescope, and what they found was nothing short of extraordinary.

The cluster appears to contain stars of two different groups, each composed of different concentrations of elements. But here's the real shocker: The two groups have an age gap of 7 billion years between them. This not only means that star formation was not continuous in Terzan 5, but that the younger group of stars somehow managed to survive being disrupted for billions of years. Their younger age combined with their connection to the older group of stars in the cluster means it could represent a sort of galactic "fossil," a remnant of what galaxies like our own Milky Way looked like in their early years, according to an ESO press release.

“Some characteristics of Terzan 5 resemble those detected in the giant clumps we see in star-forming galaxies at high-redshift, suggesting that similar assembling processes occurred in the local and in the distant Universe at the epoch of galaxy formation,“ explained Francesco Ferraro from the University of Bologna, Italy, lead author of the study.

By "high-redshift," Ferraro means galaxies that are very far away, and thus very ancient. In other words, whatever is happening within Terzan 5 is a much more recent view of what may have been happening during a time in the universe's past when galaxy formation was rampant. Studying Terzan 5 could therefore give us a chance to test theories about how the Milky Way first formed.

Terzan 5 is particularly intriguing for this purpose because its stellar population is very similar to the stellar population which can be found in the Milky Way's galactic bulge, the tightly packed region in the center of the galaxy. It's therefore apt to think of Terzan 5 as a preserved fossil of our own galaxy's early years. It's a tremendous, albeit mysterious, find.

“Terzan 5 could represent an intriguing link between the local and the distant Universe, a surviving witness of the Galactic bulge assembly process,” continued Ferraro.