The Energy Output of the Universe from 0.1 to 1000 μm

The dominant source of electromagnetic energy in the universe today ( over ultraviolet, optical, and near-infrared wavelengths) is starlight. However, quantifying the amount of starlight produced has proved difficult due to interstellar dust grains that attenuate some unknown fraction of the light. Combining a recently calibrated galactic dust model with observations of 10,000 nearby galaxies, we find that (integrated over all galaxy types and orientations) only 11% +/- 2% of the 0.1 mu m photons escape their host galaxies; this value rises linearly (with log lambda) to 87% +/- 3% at 2.1 mu m. We deduce that the energy output from stars in the nearby universe is (1.6 +/- 0.2) x 10(35) W Mpc(-3), of which (0.9 +/- 0.1) x 10(35) W Mpc(-3) escapes directly into the intergalactic medium. Some further ramifications of dust attenuation are discussed, and equations that correct individual galaxy flux measurements for its effect are provided.