Astronomers have measured the whole sky, which was leaked to the space in the entire history of the Universe. Get 4 x 1084 light particles, i.e. photons. It is roughly equivalent to all photons, which could radiate the Sun if I burned 100 billion trillion years — except that our sun has left to burn no more than 5 billion years. The Universe itself is only 13.7 billion years.
Counting all these stray photons and asking when they were rejected, may help astronomers schedule star formation over the last 11 billion years since the birth of the first stars. About the same time Marco Aiello from Clemson University in South Carolina, and his colleagues reported on 30 November in Science.
How much light is crammed into star splinter
Despite the blackness of the night sky, it contains a diffuse glow from the photons emitted long ago by the ancient stars. Astronomers call it the extragalactic background light (EBL). This glow actually captures only part of the photons ever born stars. Most stars are born in dusty environments, and most of their light is absorbed by the dust. Photons of extragalactic background light — it’s the lucky ones that went through the dust and since then travel across the space.
And since the universe is so huge, all escaped light shines no brighter than a 60 watt light bulb, flickering at a distance of four kilometers, says Aiello.
“The night sky is very, very dim but not completely dark.”
To count the photons of extragalactic background, Aiello and his colleagues took 10 years of data gamma-ray space telescope Fermi. They observed a single gamma-ray flash and 739 blazers, the light of which reached Earth 0,2 — 11,6 billion years ago. Then calculated how many gamma rays were absorbed or modified by collisions with photons of the 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 most fast the universe gave birth to stars about 10 billion years ago. Also this study will help to determine how fast the universe is expanding.