Eposode 30: Mass and Luminosity

Comic Transcript

Panel 1.
Alkina: You see? All the stars you observed going supernova were very luminous.
Professor Ahmix: Great Galaxies! You’re right!

Panel 2.
Alkina: And now if we look at the plot of luminosity versus lifetime…

Panel 3.
Professor Ahmix: Ah, well I know the mass of our sun, but not its luminosity.
Alkina: No problem, the two are closely related, what is your sun’s mass?

Panel 4.
Professor Ahmix: It’s about 4 times 10 to the 30th power kilograms.
Alkina: I see, so about 2 of our solar masses.

Panel 5.
Alkina: So here is a graph of mass vs lifetime instead. Your star falls here.

Panel 6.
Alkina: It looks like it’s below the 8 solar masses needed to go supernova.
Professor Ahmix: That’s it! You’ve got it, congratulations!

What does it mean?

Solar mass – This is a unit of mass equal to the mass of our own Sun. About 1.99 × 1030 kilograms.

In human speak please!

The mass and luminosity of a star are closely related. The more massive a star is, the more energy is required to keep it from collapsing. This energy comes in the form of heat. More massive stars burn at higher temperatures and their nuclear fuel is used more quickly, causing them to have greater luminosities. This is the same process that leads them to have shorter life spans and go supernova as their supply of nuclear fuel runs out.