As a one solar mass star evolves into a red giant, its Answer 1. luminosity increases while the surface temperature decreases. 2. surface temperature and luminosity increase. 3. surface temperature and luminosity decrease. 4. luminosity decreases while the surface temperature increases.

Question

As a one solar mass star evolves into a red giant, its Answer 	1. 	 luminosity increases while the surface temperature decreases. 	2. 	 surface temperature and luminosity increase. 	3. 	 surface temperature and luminosity decrease. 	4. 	 luminosity decreases while the surface temperature increases.

chillout · Answer

The Answer is 1)
When the star runs out of Hydrogen in its core, it starts to collapse on itself (contracts) and the adjacent shell starts heating, initiating fusion of hydrogen to helium in that shell. The increased temperature produces energy, which leads to an increased luminosity.
The expansion of the outer layers of the star makes the energy produced in the core of the star to be spread over an enormous area which results in a lower surface temperature and a redshift in the wave spectrum.