What of the following distance methods is used to determine the ...

[neverstopbelieb]

What of the following distance methods is used to determine the distance to the most distant galaxies?
 
  a. radar echo
  b. supernova observations
  c. period-luminosity relationship of variable stars
  d. parallax

Question 2

Why are massive stars more luminous than low mass stars? That is, why is there a mass-luminosity relation?
 
  What will be an ideal response?

[billybob123]

Answer to Question 1

b

Answer to Question 2

To understand the mass-luminosity relation, recall (1) the principle of hydrostatic equilibrium, which says that pressure balances weight, and (2) the pressure-temperature thermostat, which regulates energy production. A star that is more massive than the Sun has more weight pressing down on its interior, so the interior must have a higher pressure to balance that weight. That means the massive star's automatic pressure-temperature thermostat must keep the gas in its interior hot and the pressure high. A star less massive than the Sun has less weight on its interior and thus needs less internal pressure; therefore, its pressure-temperature thermostat is set lower. Massive stars are more luminous because they must make more energy to support their weight.