Milky Way's building blocks still sparkle in the sky
© NASA/ESA/Hubble SM4 ERO Team
Jae-Woo Lee of Sejong university in Seoul, South Korea, and his colleagues re-examined 37 of the clusters, and found that more than half of them hold two distinct populations of stars. One population seems to have more complex chemistry than the other, containing high levels of calcium.
This calcium and other heavy elements could have been created in supernova explosions, and then incorporated into new stars, but the clusters as they are today are too small to keep hold of the material violently thrown out by supernovae. This suggests that the clusters are the remnants of entire dwarf galaxies.
original source (for full reading needs nature-login): Nature