Star Clusters: Crash Course Astronomy #35

Summary

This script delves into the cosmos of star clusters, distinguishing between open and globular clusters. Open clusters, young and loosely bound, consist of dozens to thousands of stars, while globular clusters, very old and dense, contain hundreds of thousands of stars. The script explains the formation, characteristics, and eventual dissolution of open clusters, and the enduring nature of globular clusters, which are rich in stellar remnants and offer a unique view of the universe's early stages.

Takeaways

• 🌌 Stars can form in groups, with the number of stars determining the type of system: binary for two stars, trinary for three, and so on.
• 🌟 Most stars are believed to be born in clusters, which can contain hundreds to millions of stars, indicating a common origin.
• 🔍 There are two main types of star clusters: open (or galactic) clusters and globular clusters, each with distinct characteristics.
• 🌠 Open clusters are loosely bound groups of dozens to thousands of stars, often irregular in shape and visible to the naked eye as faint patches.
• 🌌 Open clusters are formed from massive clouds of gas and dust, with local conditions determining the number of stars formed.
• 🌟 The stars in an open cluster orbit the cluster's center of mass, contributing to a collective gravitational pull, unlike the solar system's central gravity from the Sun.
• 🚀 Open clusters are typically a few dozen light years across, with stars closer together than in interstellar space, indicating a dense environment.
• 🌠 The age of open clusters can be determined by observing the most massive stars still on the main sequence, providing insights into their formation and evolution.
• 🌌 Globular clusters are massive, spherical collections of hundreds of thousands of stars, with a well-defined core and a halo that fades with distance.
• 🌟 Globular clusters are very old, some over ten billion years, and are thought to be among the first objects to form after the Universe itself.
• 🌠 The stars in globular clusters are denser and have fewer heavy elements, suggesting an older generation of stars formed before the Universe was enriched with heavier elements.

Q & A

What is the term used to describe a system of two stars orbiting each other?

A binary system.

What are the two types of star clusters mentioned in the script?

Open clusters and globular clusters.

How do open clusters form?

Open clusters form from gigantic clouds of gas and dust, where local conditions can lead to the formation of dozens, hundreds, or thousands of dense clumps that contract to form individual stars.

Why are open clusters typically not as old as globular clusters?

Open clusters are typically younger because they evaporate over time due to gravitational interactions between the stars, which change their orbits and eventually cause stars to be flung out of the cluster.

How can the age of a star cluster be determined?

The age of a star cluster can be determined by observing the most massive stars still on the main sequence, as these stars are fusing hydrogen into helium. Their spectra can be used to identify their mass, which in turn helps determine the cluster's age.

What is the Pleiades and why is it significant?

The Pleiades is a famous open cluster about 500 light years from Earth, appearing as a small, tightly-packed collection of stars. It is significant because it is one of the few clusters visible to the naked eye and is embedded in a dust cloud.

How are globular clusters different from open clusters in terms of structure?

Globular clusters are larger, have hundreds of thousands of stars, and are more spherical in shape compared to open clusters. They also have a well-defined core with stars scattered around them in a halo that fades away with distance.

Why are globular clusters considered to be very old?

Globular clusters are considered very old because most of the stars in them are less massive than the Sun, indicating that they have been around long enough for even stars like the Sun to become red giants and die.

What is the significance of the presence of blue stragglers in globular clusters?

Blue stragglers in globular clusters are significant because they are stars that have physically collided and merged to form a single, higher mass star. This is a rare phenomenon in space but more common in the tightly packed environment of globular clusters.

Why might it be unlikely for planets like Earth to form in globular clusters?

It is unlikely for planets like Earth to form in globular clusters because the stars in these clusters lack heavy metals, which are necessary for planet formation. Additionally, the closely packed stars could eject any planets that did form due to nearby encounters.