Answer:
A) supergiants have a higher absolute brightness than the Sun.
D) white dwarfs have a lower absolute magnitude than the Sun.
Explanation:
The Hertzsprung-Russel diagram is a diagram representing:
- The surface temperature of the star on the x-axis (on a decreasing scale, so from higher to lower)
- The absolute brightness (luminosity) of the stars on the y-axis
The H-R diagram is characterized by the presence of a diagonal line going from the top left corner to the bottom right corner, and this line contains most of the star. Stars along this diagonal are the stars in the main sequence, which is the longest stage of life of a star, characterized by a stability due to the balance between the gravitational inward pressure and the outward radiation pressure of the star.
However, supergiant stars are located outside this diagonal, and in particular in the top right corner of the diagram (in fact, these stars have a very high luminosity but a lower temperature).
On the other hand, white dwars are also located outside the main sequence diagonal, having a lower luminosity and a higher temperature (so they are located in the bottom left corner).
The Sun, instead, is located approximately at the center of the main sequence diagonal.
Therefore, the correct option is
A) supergiants have a higher absolute brightness than the Sun.
D) white dwarfs have a lower absolute magnitude than the Sun.
