Which of the Following Sources Contributes the Greatest Number of Photons

question 17

Multiple Choice

Which of the following sources contributes the greatest number of photons to the general radiation background in our universe?

• A) The cosmic microwave background,the remnant of the Big Bang
• B) The very large number of average solar-type cool stars,contributing vast numbers of visible and infrared photons
• C) Atomic hydrogen,which is very abundant throughout the universe,contributing mainly 21-cm radio photons.
• D) Extremely hot intergalactic gas in clusters of galaxies,producing copious numbers of X-ray photons

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