Young Stars & Stellar Associations

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  • 0:02 Association Rules and Fees
  • 0:41 What is an Association?
  • 1:45 T, R, & OB Associations
  • 3:12 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will describe the concept of a stellar association for you and how it differs from a star cluster. You'll also learn about the three general kinds of stellar associations: R associations, T associations, and OB associations.

Association Rules and Fees

I may never be able to buy an apartment as a result of this, but I'm just gonna say it: I generally dislike homeowner associations. Associations are the organizations that take a property owner's money for things that, often times, they don't even want or need, but it's supposedly for the good of the community.

You may own your own home, but you still have to follow the rules associations set and pay the fees they charge you. To me, that makes little sense most of the time since I can't do anything with my property unless someone else, someone who doesn't own it, approves of what I want to do with it. So, as I've grown older, I've moved away from any properties associated with, well, associations.

Stars also appear to dislike pesky associations, and move away from them with time as well.

What Is an Association?

In the world of astronomy, an association is a loose collection of stars (roughly 10 to 100) moving together through space but not bound to one another by gravity. This means that these stars do not move in a star cluster, a collection of relatively tightly-bound stars moving together through space and held together by way of gravitational attraction to one other.

In star clusters, the stars like one another and stick close by. Associations, however, are a bunch of young stars that simply haven't had the time to move far away from the gas clouds from which they formed.

It's not clear why some gas clouds give rise to a star cluster and others give birth to associations, however. What is known is that the vast majority of stars begin their life as part of an association. But maybe because they don't like their association's rules or fees or whatever, they move away from the association with time - within a few million years, that is.

T, R, & OB Associations

Not all associations are created equal, so I'm sure there are good homeowners associations I don't want to receive any letters about.

Not all stellar associations are the same either.

  • T Associations are large groups of T Tauri stars.
  • OB Associations are groups of very young stars consisting of spectral types O and B.
  • R Associations are groups of bright young stars of intermediate mass illuminating reflection nebulae.

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