Astronomers have measured all the light of the stars ever issued

Astronomers have measured all the light of the stars that managed to escape into space during the history of the universe.

It is equivalent to 4 x 10⁸⁴ light particles 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 misled photons and determining when they were emitted can help astronomers write a timeline of star formation over the last 11 billion years since the birth of the first stars, explained the Astrophysicist Marco Ajello of Clemson University in South Carolina in November. 30 Science.

Despite the darkness of the night sky, it contains the diffuse glow emitted by the photons emitted by the ancient stars, what astronomers call the extragalactic background light, 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 EBL photons are the lucky ones who have managed to get out of the dust and travel to space since that time.

And yet, as the universe is so immense, all that escaped the light shines only through a 60-watt light bulb seen from a distance of four kilometers, explains Ajello.

"The night sky is very very dark," says Ajello, but "he is not completely black".

This light is too weak and too scattered to be located 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 of the EBL layer, 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 layer.

"This allows us to understand the formation of galaxies and stars throughout 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 measure could also help to determine the speed at which the universe is developing (SN: 3/4/17, p. 18).

Measuring EBL provides an independent way to cross-check 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 more by the community."