Astronomers measured all the light of the stars ever issued

During the history of the universe, astronomers measured all the stellar light that managed to escape into space

which equates to 4 x 10 ⁸⁴ particles of light, or photons. That's roughly equivalent to all the photons that the sun would emit if it burned for $ 100 billion – well over the remaining $ 5 billion. The universe itself is only 13.7 billion years old.

Measuring all these parasitic photons and determining their date of emission can help astronomers to write a timeline of star formation over the last 11 billion years since the birth of the first stars, astrophysicist Marco Ajello of Clemson University in South Carolina and his colleagues report in the November 30 edition of Scienc e.

Despite the darkness of the night sky, it contains the diffuse glow emitted by photons long emitted by ancient stars, which astronomers call the extragalactic background light, or EBL ( SN: 9 / 7/13, p 22 ). This glow actually captures only a fraction of the photons ever produced in the stars. Most stars are born in dusty environments and most of their light is absorbed by dust. The photons of the EBL layer are the lucky ones who managed to get out of the dust and to travel in space since.

And yet, because the universe is so huge, all that escaped the light shines as brightly as a 60 – According to Ajello, a bulb of a watt was seen at four kilometers away.

"The night sky is very dark," said Ajello, "but it's not completely dark."

This light is too dark and too wide. locate directly, even with the most powerful telescopes. Ajello and his colleagues researched the interaction of EBL with the gamma rays emitted by powerful distant blazars. Blazars are active black holes that send white-hot radiation jets into the universe. Their light can reach us in billions of light years.

To establish the photon count in the EBL, Ajello and his colleagues used 10 years of data from the Fermi Gamma space telescope. The team observed an explosion of gamma rays and 739 blazars whose light reaches the Earth 0.2 to 11.6 billion years ago. Then they calculated how many gamma rays had been absorbed or modified by photon collisions in the EBL.

"This allows us to understand the formation of galaxies and stars in the history of the universe," says Ajello. For example, the data confirmed that the universe was creating stars most rapidly about 10 billion years ago, he says. The measurement could also help determine the rate of expansion of the universe ( from SN: 3/4/17, p.18 ).

The EBL measurement provides an independent means of cross-checking other measurements made with visible light telescopes, says astrophysicist Elisa Prandini of the University of Padova in Italy. "It's a treasure, this huge data set and this EBL measurement they've done," she says. "It will be used later by the community."