Scientists Explore Missing Star Mystery in Small Dwarf Galaxy's Globular Clusters

While most new information is supposed to solve mysteries, some recent findings have merely deepened them. New observations of globular clusters in a small galaxy, called Fornax, show that they are very similar to those found in the Milky Way, and so must have formed in a similar way. Yet theories predict that globular clusters should only be found nestled among large quantities of old stars; while these stars are present in the Milky Way, they're not found in the small galaxy.

Globular clusters are large balls of stars that orbit the centers of galaxies. Once thought to be formed out of a single population of stars that all formed together, globular clusters are far more complex than that. In fact, studies of the Milky Way's globular clusters have shown that many are made up of at least two distinct populations of stars, if not more.

In globular clusters, one population of stars is usually a single generation of normal stars; these form first. The second population is a second generation of stars which are populated with different chemical elements.

In this case, the researchers found that the proportion of polluted stars in the Milky Way's globular clusters was far higher than expected. This suggests that a large chunk of first generation star populations is missing. It's possible that these stars might have been ejected from the cluster at some time in its past.

More interesting, though, is that the clusters within the small galaxy also contain a second polluted population of stars. This suggests that they formed in a similar manner to those in the Milky Way. Based on the number of polluted stars in these clusters, they would have been up to ten times more massive in the past. Unlike in the Milky Way, though, the galaxy that hosts these clusters doesn't have enough old stars to account for the huge number that were supposedly ejected.

"If these kicked-out stars were there, we would see them-but we don't!" said Frank Grundahl, co-author of the new paper, in a news release. "Our leading formation theory just can't be right. There's nowhere that Fornax could have hidden these ejected stars, so it appears that the clusters couldn't have been so much larger in the past."

The findings are published in The Astrophysical Journal.