Question

Why do elliptical galaxies appear red in color?

a) Their blue stars are too dim to be resolved by telescopes.

b) They don't have enough gas to form new stars.

c) Only low-mass red stars can form in ellipticals.

d) They are all moving away from the Milky Way at high speeds and their light is red shifted.

Answer 1

Ans : B.

Explanation

A galaxy is a collection of stars, and we know that when stars evolve they become more red. Therefore, since no new stars form in an elliptical galaxy then ellipticals become more red as they age.

All galaxies are the color of their brightest stars. In fact, 99% of a galaxy's light is emitted by the brightest 1% of the stellar population present. Lack of dust clouds means that star formation has ceased in these galaxies, long enough ago that there are no blue main sequence stars (OB types). The color is dominated by cool giant stars of luminosity class I. These stars are red. Therefore ellipticals are red.