Hubblecast 80: The riddle of the missing stars

Summary

New Hubble observations challenge the prevailing theory on the formation of globular clusters, which are dense star groupings orbiting galaxies. Traditionally believed to be made of a single generation of stars, recent findings suggest these clusters contain a second, chemically distinct generation. The discovery of similar clusters in the smaller Fornax galaxy, which lacks the older stars needed to support the ejection theory, prompts astronomers to reconsider the origins of these stellar formations.

Takeaways

• 🌌 Globular clusters are dense groups of stars that orbit galaxies, including the Milky Way.
• 🔍 Previously, globular clusters were thought to consist of a single group of stars formed simultaneously.
• 🤔 The Milky Way's globular clusters are more complex, with at least two distinct groups of stars.
• 👥 About half of the stars in these clusters are a first generation of normal stars, and the other half are a second generation with more chemical pollution.
• 😮 Astronomers were surprised to find more second-generation stars in the Milky Way's clusters than expected.
• 💭 A leading theory suggested that globular clusters once had many first-generation stars, some of which were later ejected.
• 🌌 This theory would fit for clusters in the Milky Way, where ejected stars could blend into the galaxy's halo.
• 🔬 New Hubble observations examined globular clusters in the smaller Fornax galaxy, challenging the previous theory.
• 😯 The Fornax galaxy's clusters are similar in composition to those in the Milky Way but lack the older stars needed for the ejection theory.
• 🤷‍♂️ The findings indicate that the current leading theory on the formation of mixed-generation clusters may be incorrect.
• 🌟 Astronomers will need to reconsider the origins of these mysterious stellar formations in the Milky Way and beyond.

Q & A

What are globular clusters?

Globular clusters are dense, spherical collections of stars that orbit galaxies, including our own Milky Way.

What was the initial understanding of the formation of globular clusters?

Initially, it was believed that globular clusters consisted of a single group of stars that all formed together at the same time.

Why are the Milky Way's globular clusters considered complex?

The Milky Way's globular clusters are complex because they are made up of at least two distinct groups of stars, with different generations and chemical compositions.

What is the composition of the two distinct groups of stars in globular clusters?

About half of the stars in these clusters are a single generation of normal stars, and the other half form a second generation that is more chemically polluted due to the presence of elements produced by the earlier stars.

Why were astronomers baffled by the proportion of second-generation stars in the Milky Way's clusters?

Astronomers were baffled because there were many more second-generation stars than expected, suggesting a more complex formation history than previously thought.

What was the leading explanation for the high number of second-generation stars?

The leading explanation was that globular clusters originally contained a large number of first-generation stars, some of which were later ejected from the cluster.

How does the ejection of first-generation stars relate to the globular clusters in the Milky Way?

The ejected first-generation stars could potentially hide among the many similar stars in the vast halo of our galaxy, providing a plausible explanation for the observed star proportions.

What new observations have challenged the leading theory of globular cluster formation?

New Hubble observations of globular clusters in the smaller Fornax galaxy have shown that the same theory does not hold, as there are not enough older stars in the galaxy to support the ejection theory.

Why is the Fornax galaxy significant in the study of globular clusters?

The Fornax galaxy is significant because its globular clusters are similar in composition to those in the Milky Way, but the galaxy does not have enough older stars to support the ejection theory, challenging the existing explanation for cluster formation.

What does the finding in the Fornax galaxy imply for the theory of globular cluster formation?

The finding implies that the leading theory on how mixed-generation clusters formed is incorrect, as there is no evidence of the necessary older stars being present in the Fornax galaxy.

What is the Hubble mission and its purpose?

The Hubble mission is an international project between NASA and the European Space Agency aimed at studying the universe through the Hubble Space Telescope, providing valuable data and insights into celestial objects such as globular clusters.