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Astronomers have measured all the starlight that has seeped into space in the history of the Universe. It turned out 4 x 1084 particles of light, that is, photons. This is roughly equivalent to all the photons that the Sun could radiate if it burned 100 billion trillion years — only now our luminary has no more than 5 billion years to burn. The Universe itself is only 13.7 billion years old.
Counting all these stray photons and figuring out when they were emitted can help astronomers plot star formation over the last 11 billion years, starting with the birth of the first stars. Marco Ayala of Clemson University in South Carolina and his colleagues reported about it on November 30 in Science.
How much light is crammed into star splinter
Despite all the blackness of the night sky, it contains a diffuse glow from the photons emitted long ago by ancient stars. Astronomers call it the extragalactic background light (EBL). This glow actually captures only a fraction of the photons ever born by stars. Most stars are born in dusty environments, and most of their light is absorbed by dust. Photons of extragalactic background glow are the lucky ones who have passed through the dust and have been traveling through space ever since.
And because the universe is so vast, all of the escaped light shines no brighter than a 60-watt bulb flickering four kilometers away, says Aiello.
“The night sky is very, very dim, but not quite dark.”
To calculate the photons of the extragalactic background, ayello and his colleagues took 10-year data from the gamma-ray space telescope Fermi. They observed one gamma-ray flash and 739 blazars, the light of which reached the Earth 0.2 — 11.6 billion years ago. Then we calculated how many gamma rays were absorbed or altered by collisions with photons in EBL.
“This allows us to understand the formation of galaxies and stars throughout the history of the Universe,” says Aiello. For example, the data confirmed that the fastest the universe produced stars was about 10 billion years ago. Also, this study will help determine how fast the universe is expanding.
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