The total luminosity of the stars in our galaxy isL≈3×1010L. Suppose that the luminosity of our galaxy has been constant for the past 10 Gyrs. How much energy has our galaxy emitted in the form of starlight during that time? Most starsare powered by the fusion of H into4He, with the release of 28.4 MeV for every helium nucleusformed. How many helium nuclei have been created within stars in our galaxy over the course ofthe past 10 Gyrs, assuming that the fusion of H into4He is the only significant energy source? Ifthe baryonic mass of our galaxy isM≈1011M, by what amount has the helium fraction Y ofour galaxy been increased over its primordial valueY4= 0.24?