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 μm photons escape their host galaxies; this value rises linearly (with log λ) to 87% ± 3% at 2.1 μm. We deduce that the energy output from stars in the nearby universe is (1.6 ± 0.2) × 1035 W Mpc−3, of which (0.9 ± 0.1) × 1035 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.