Most of the globular clusters found in the Milky Way were created when the galaxy first formed roughly 13 billion years ago, while some of them are faint, sparsely populated systems that were only discovered within the past five decades or so, according to a new study.
Among those so-called ghosts from the galaxy’s past is ESO 37-1 (E3), a poorly studied globular cluster first located in 1976 which had never been the subject of spectroscopic observations. That is, until now, as a team of European astronomers analyzed it in this way for the first time.
E3, an extremely faint spherical-shaped grouping of stars, is one of some 200 such objects in the Milky Way, but few have so piqued the interest of researchers. As they wrote in a recent edition of the journal Astronomy & Astrophysics, it is a ghost from the galaxy’s past that has long been hidden behind younger, brighter objects found closer to Earth.
“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,” study co-author Carlos de la Fuente Marcos explained in a statement. “They were formed when our galaxy was virtually new-born, 13 billion years ago.”
Cluster’s characteristics indicate it was created all at once
Using the European Southern Observatory’s Very Large Telescope (VLT) in Chile, de la Fuente and his colleagues analyzed E3 and found that it had far fewer stars than most globular clusters—just a few tens of thousands compared to hundreds of thousands or even millions.
In addition, the cluster located the regular circular symmetry found in such objects. Instead, he added, it had a far more distorted rhomboidal shape distorted by galactic gravitational waves. A previous study also found that it is chemically homogeneous—or lacking variety in terms of the different types of stars that can be found within 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,” said de la Fuente Marcos. “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.” These findings, he added, “enable us to gain insight into the infancy of the Milky Way.”
Even with the new data, astronomers still need to verify that this cluster actually formed within the Milky Way, and was not pulled into the galaxy from elsewhere. De la Fuente Marcos said he and his colleagues hope to conduct additional research into the issue starting next year.
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