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All the light of all the stars that have ever existed. It's a quantity of unimaginable magnitude, but now astronomers have put a number.
From the oldest weaker stars to the largest galaxies, an international team managed to measure the total amount of stellar light emitted over the entire 13.7 years Bnn years of history. universe.
"This has never been done before," said Marco Ajello, an astrophysicist at Clemson College of Science in South Carolina and senior author of the journal.
a few hundred million years after the big bang. Since then, galaxies have produced stars at a staggering rate, and scientists estimate about 1 trillion trillion
In total, astronomers estimate that the stars radiated 4×10 84 (a photon in progress). the smallest unit of light). In other words: 4,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 photons.
Astronomers based their calculations on measurements of extragalactic background light (EBL), a cosmic fog of accumulated radiation. More than 90% of the starlight eventually survives in this dark radiation context.
"Today we are in this ocean of light," said Kári Helgason of the University of Iceland in Reykjavík and paper.
Since it has been obscured by the light of neighboring stars, the EBL has proved difficult to study.
The latest observations, collected over the past nine years by NASA's Fermi Space Telescope, use the light of blazars – super mbadive black holes that emit powerful gamma rays – as beacons to illuminate the cosmic fog . "They are so brilliant that they can shine on almost any observable universe," Helgason said.
In total, the team captured the signals of 739 blazars – some relatively close and others extremely distant, whose light was emitted in the ancient universe. It took billions of years to get to Earth.
Gamma-ray photons traveling in a stellar light fog are likely to be absorbed. Thus, by taking blazars at different distances from the Earth and calculating the amount of radiation lost along the way, we were able to determine the total light of stars at different periods of time.
"We measured the total light of the stars of each era – 1 billion years ago, 2 billion years ago, 6 billion years ago, all went back to the Era of star formation, "said Vaidehi Paliya, co-author of the newspaper, also from Clemson.
" It's really this cast that gives us the opportunity to restore light "An additional complication is that, while starlight accumulates over time, cosmic fog is simultaneously diluted as the universe gets darker," says Helgason
. expands and that the space itself expands .. Overall, the fog becomes ever denser.This phenomenon and other complex phenomena have been taken into account in the use of & # 39; 39, a computer model.
The measurements suggest that the formation of stars has peaked there about 11 billion years ago and that it has been declining ever since. Each year, about seven new stars are created in our Milky Way galaxy.
The results, published in the journal Science, are consistent with previous indirect estimates of total starlight based on galaxy surveys. "It's really satisfying when two methods give you the same answer," Helgason said.
The data also provide new information about the first billion years of the history of the universe, an era that has not yet been probed by current satellites. [19659002] "Our measurement allows us to take a look inside," Ajello said. "Maybe one day we will find a way to wind up to the big bang. This is our ultimate goal. "
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