Date: December 10, 2009

Title: Blue Star Blues

Podcaster: Mel Blake, Ashley Wills and Cara Depew

Organization: http://www.una.edu/physics
http://www.una.edu/planetarium

Description: A giant, blue B star is singing the Blues. Why might our large bright friend be feeling this way? What is a B star anyway? Where did it come from and what will happen to it? We will discuss the B-star and cheer it up by showing the very important role that these short-lived massive stars play in the galaxy and the origin of life.

Bio: Dr. Mel Blake is director of the University of North Alabama Planetarium and Observatory operated by the department of Physics and Earth Science. When not conducting planetarium programs for schools and the public he conducts research on binary and variable stars.

Ashely Wills and Cara Depew are undergraduate students enrolled in the honors program at University of North Alabama.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Craig Clark.

Transcript:

B-Star Blues

Me on Harp.

I got the Blue-star blues
I got the Blue-star blues
Some stars are red,
Some stars are yellow
But one thing is true,
One of the brightest of them all are giant and blue
The Blue-star blues

Student 1. Mister Blue-star, why do you have the blues?

Student 2. Yeah. You seem pretty impressive to us.

B-star. What do you mean?

Student 1. Well, lets see. First of all, you are a B star. This means you are among the brightest stars in the Universe. Only the O-stars are brighter.

B-star. Hey, wait. I didn’t know I was a B star. I just thought I was blue.

Student 2. Well, you are blue but you are also a B star. We classify stars based upon their temperatures, brightnesses and sizes. It all started with Annie Cannon at Harvard College Observatory. She was given the job of trying to classify hundreds of spectra coming from telescopes about 100 years ago.

Student 1. She eventually devised a system with spectral types based upon the hydrogen features in the light of the stars. She had to study the light from thousands of stars. Her system tells us a lot about the stars.

Student 2. The letters go OBAFGKM. The hot stars are O and B stars, like you. The cool stars are K and M stars. Also, you are a large star, a blue super giant star. That makes you one of the brightest stars in the Universe.

B-star. OK. But why aren’t the letters in order?

Student 1. Its because the processes that caused the features in starlight from the different chemical elements wasn’t fully understood when Annie Cannon did this. So there was some trial and error involved.

Student 2. It was only when Celia Payne was able to show that the spectral types were related to temperature that a full understanding of the spectral sequence came about.

B-Star. But you say I am a B star and I’m blue. How does that relate to temperature? I just kinda thought all the other stars near me were puny.

Student 1. Well, a scientist by the name of Max Planck studied the physics of radiation from different objects. What he discovered was that stars emit light at different colors depending upon temperature. It turns out that the hotter stars emit lots of light in the blue or even ultraviolet light humans can’t even see.

Student 2. So you are really hot, which makes you blue. It also means you are really bright as well.

Student 1. Some B-stars have so much radiation that the outer layers form a stellar wind. We see gas streaming off them into space. We call these Be stars.

Student 2. You don’t seem to be a Be star.

B-star. I don’t know if that is good or bad. Oh well. At least I have neighbors.

Student 1. That’s because you are in a star cluster, a very young open cluster.

B-star. Why do you say young? I am 1 million years old!

Student 2. That’s young for a star. Some stars are billions of years old. Most stars form in clusters, anywhere from a few dozen to thousands of stars. The fact that you are even in the cluster tells us that the cluster is very young.

B-star. Why is that?

Student 1. We’ll astronomers can use the laws of physics to study stars. They discovered that stars shine mostly by converting light elements into heavier elements. Some matter in the stars in converted to energy.

Student 2. Yes. Albert Einstein’s theory tells us that matter and energy are the same, through his famous equation e = mc2

B-star. What does that have to do with my cluster being young?

Student 1. Well, even though you are large, the nuclear reactions in your core run through fuel very fast. As a result you produce a lot of energy very quickly. You are about twenty times more massive than our own Sun.

Student 2. So you will only last about 10 million years. That means your clusters can’t be older than that. After all, you can’t be older than the clusters of stars you formed in.

B-star. Wow. I thought I had more time than that. Its even more depressing. What happens then?

Student 1. In your core you are producing heavy elements. However, you will eventually get to the element iron.

Student 2. Iron fusion will rob energy from your core, and cause the core to collapse. The outer layers will fall and rebound and you’ll blow up in a supernovae explosion.

Student 1. Your explosion will be as bright as an entire galaxy.

B-star. Well, I’ll literally go out with a bang. I kinda thought my interior was changing fast. That’s why I had the blues.

Student 2. You shouldn’t. When you explode, you will produce many heavy elements; a lot of these heavy elements are needed for life in the Universe.

Student 1. So humans are literally made of the remains of stars that exploded!

B-star. So without me, life could not happen in the Universe. I feel a lot better.

Student 1 & 2. Glad we could cheer you up!

I got the Blue-star blues
I got the Blue-star blues
I big, I’m bright,
Lots and lots of light!
But bright don’t last
There’s gonna be a blast!

End of podcast:

365 Days of Astronomy
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