“Probability factor of one to one “Probability factor of one to one...we have normality, I repeat we have normality. Anything you still can't cope with is therefore your own problem.” The Hitchhiker's Guide to the Galaxy Group Project is due: please put a symbol below your names, as they will be scanned and posted on-line. I’ll collect them in a few minutes after class begins. Reading updated for the entire section on stars.

This is what random (unrelated) looks like In science, if we can measure 2 things, we plot them against each other and look for relationships. This is what random (unrelated) looks like

This is not random Blue Red

The stars fall into groups The stars fall into groups. The group where we see the most stars is called the Main Sequence. Stars of similar temperature, but brighter are called Red Giants, and smaller stars are called white dwarfs.

About this plot: The X axis- Temperature- hotter to the left, cooler to the right. Color: blue is hot, red is cool And spectral types

Spectral type mnemonic Oh Be A Fine Girl/Guy Kiss Me I like: Oh Boy! Astronomy Faculty Get Killed Monday

So what determines where a star is in the HR diagram?

Russell-Vogt theorem: A star's location on the HR diagram is determined by only 3 things: its mass, age, and (barely) composition.

On the main sequence, what is the underlying relationship? HR Diagram Why are the stars in different regions? What makes a main sequence star that is red and faint (Star A) different from a main sequence star that is hot and bright (Star B) ? On the main sequence, what is the underlying relationship?

MASS HR Diagram The difference between this star and this star is Blue Red

HR Diagram What are the masses of stars at the top and bottom of the main sequence? Blue Red

HR Diagram 100-200 MSun at the top and about 0.02MSun at the bottom. Blue Red

That is L=M3.5=MxMxMx(M1/2) In solar units (the Sun=1). We will start with mass. Along the main sequence, luminosity goes as mass to the 3.5 power. That is L=M3.5=MxMxMx(M1/2) In solar units (the Sun=1).

On the main sequence, luminosity goes as mass to the 3.5 power. That is L=M3.5=MxMxMx(M1/2) In solar units (the Sun=1). Let's try one: How bright (compared to our Sun) is a 4 solar mass star?

On the main sequence, luminosity goes as mass to the 3.5 power. That is L=M3.5=MxMxMx(M1/2) In solar units (the Sun=1). Let's try one: How bright (compared to our Sun) is a 4 solar mass star?

On the main sequence, luminosity goes as mass to the 3.5 power. That is L=M3.5=MxMxMx(M1/2) In solar units (the Sun=1). Let's try one: How bright (compared to our Sun) is a 4 solar mass star? This MS star is 128 times brighter than our Sun.

The Pistol star is about 100-200MSun Upper range for mass: The Pistol star is about 100-200MSun However, stars that big are extremely rare.

If the Pistol star is 100MSun how bright should it be. L = M3 If the Pistol star is 100MSun how bright should it be? L = M3.5 = M1/2xMxMxM

If the Pistol star is 100MSun how bright should it be. L = M3 If the Pistol star is 100MSun how bright should it be? L = M3.5 = M1/2xMxMxM = 10 million!

Gliese 229B is in a binary with a Red Giant star Gliese 229B is in a binary with a Red Giant star. It is only 20-50 times more massive than Jupiter or 0.019MSun. (How bright?)

Gliese 229B is 0.019MSun. How bright? L=(0.019)3.5 = 9.5x10-7 = 0.00000095 9.5 ten-millionths!

Do stars with more mass live longer or shorter? So stars can get ~200 times the mass of the Sun, but millions of times brighter. What does that mean for fuel consumption? Do stars with more mass live longer or shorter?

Q10: Which should go farther? A) The large star (Hummer with a 50 gallon tank). B) The small star (Metro with a 10 gallon tank).

Massive stars have shorter main sequence lifetimes. They have more mass, so more fuel to burn, but have to burn it quicker to support their massive weight. tMS=1x1010/M2.5=1x1010/(MxMxM1/2) in years. If you put in mass in solar units. So for M=1 (our sun), t=1x1010=10 billion years.

Stellar lifetimes. So our Sun will be on the main sequence for 10 billion years. What about the Pistol Star (assuming 100 solar masses)? tMS=1x1010/(MxMxM1/2)

Stellar lifetimes. So our Sun will be on the main sequence for 10 billion years. What about a star with 100 solar masses? t=1x1010/1002.5=1x1010/(100x100x10)=1x1010/105=105 Only 100,000 years!

What about a star with 0.04 solar masses? Stellar lifetimes. So a star with 100 solar masses only remains on the main sequence 100,000 years. What about a star with 0.04 solar masses? t=1x1010/0.042.5=1x1010/(0.04x0.04x0.2)=?

What about a star with 0.04 solar masses? Stellar lifetimes. So a star with 100 solar masses only remains on the main sequence 100,000 years. What about a star with 0.04 solar masses? t=1x1010/0.042.5=1x1010/(0.04x0.04x0.2)=1x1010/0.00032= 3x1013 years. (30 trillion!)

Relations on the main sequence Relations on the main sequence. How bright a star is on the main sequence depends on its mass. How long a star is on the main sequence depends on its mass. These equations use solar units (mass and luminosity)

So what? So what's the big deal about the main sequence lifetime, or why are most stars we see on the main sequence? Stars spend 90% of their lifetime (some kind of energy generation) on the main sequence.