Question

Hundreds, even thousands of stars may be easily observed in the night sky. What process produces the light from the stars?

A.
radioactive decay of heavy elements
B.
chemical combustion of hydrogen
C.
nuclear fusion, in which atomic nuclei combine
D.
gravitational waves, released by the high mass of stars

Answer 1

C. Nuclear fusion, in which atomic nuclei combine.

In stars' cores hydrogen nuclei fuse into helium (via the proton–proton chain in stars like the Sun, or the CNO cycle in more massive stars), releasing energy as photons (light) and neutrinos by converting mass to energy (E = mc^2). Chemical burning, radioactive decay, or gravitational waves do not account for the enormous sustained luminosity of stars.