Back in 2018, a team of astronomers and astrophysicists measured all of the light in the history of the observable universe.
Marco Ajello, an astrophysicist at Clemson University, led the team that used NASA's Fermi Gamma-ray Space Telescope to view all of the light within the observable universe bubble, which is estimated to be about 14 billion light-years in radius. This bubble represents how far researchers are able to see back in time to the beginning of the universe, and so far researchers know that the observable universe contains, "contains at least two trillion galaxies and a trillion trillion stars," writes Dennis Overbye in New York Times Science.
Ajello and his team analyzed all of the relevant data acquired by NASA's Fermi Gamma-ray Space Telescope and found, "From data collected by the Fermi telescope, we were able to measure the entire amount of starlight ever emitted. This has never been done before. Most of this light is emitted by stars that live in galaxies. And, so, this has allowed us to better understand the stellar-evolution process and gain captivating insights into how the universe produced its luminous content", says Ajello.
Additionally, researchers were able to measure how many photons, or particles of visible light that can be seen with the naked eye, in the observable universe - arriving on 4x10^10, or -
4,000,000,000,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000, 000,000,000,000,000,000,000 photons.
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