A surprising fact about galactic astronomy is that we know more about other galaxies than our own. The Solar System is not in a great place to learn all there is to know about the Milky Way. The origin of our galaxy is still very mysterious, but we might have found a way to learn more about it.
A team of Spanish and Italian astronomers were the first to study the globular cluster called E 3 in detail. Globular clusters are spherical groups of stars that tend to have formed together, so they have approximately the same age. The team discovered a very old system that formed at the very dawn of the Milky Way, with a chemical composition that is a lot richer than we expected.
The results have been published in a paper titled "Ghosts of Milky Way’s past" in the journal Astronomy & Astrophysics.
"This globular cluster, and a few similar ones – such as Palomar 5 or Palomar 14 – are `ghosts´ because they appear to be in the last stages of their existence, and we say ´from the past´ because they are very old," said Carlos de la Fuente Marcos, one of the authors, in a statement. "They were formed when our galaxy was virtually new-born, 13,000 million years ago."
"Unlike typical globular clusters, which contain hundreds of thousands and in some cases millions of stars, the object studied only has a few tens of thousands of them."
The Sun belongs to the latest generation of stars that are described as metal-rich, because a small percentage of their mass is made up of elements heavier than hydrogen and helium. Older stars tend to be metal-poor, but the chemical composition of this globular cluster shows the stars having 20 percent of the metallicity of the Sun. This discovery suggests that the metal enrichment started very early in the history of the Milky Way.
This chemical composition is shared among all the stars that are members of the cluster. "This is characteristic of an object that was created in block, in one single episode, like what is supposed to have happened when our galaxy was born: very large star clusters (containing millions of stars) were formed, but what remains of them today are objects like E 3, ghosts from a distant past," said De la Fuente Marcos.
The team will continue to study the cluster in 2016 in the hope of answering more questions about the origin of this fascinating object.