The new calculation of Total Starlight defers scientists in cosmic time

If you're a fan of big numbers who do not talk much to you about the world, Clemson University astrophysicist, Marco Ajello, has an excellent one: 4 x 10 ^ 84.

This is the total number of photons that have escaped from the stars and the dust that surrounds them in space during the history of the universe. You would expect that value to be enormous, of course, and here it is in all its incomprehensible extent. (For comparison, a recent estimate of the number of atoms in the universe is a few orders of magnitude lower.)

However, being able to calculate this number is only a big advantage for the new research conducted by Ajello and his team. This research backs up previous theories on star formation rates during the history of the universe, using information trapped in all this starry light – known officially as Light of the Universe. extragalactic background. [Gamma-Ray Universe: Photos by NASA’s Fermi Space Telescope]

The extragalactic background light is, by definition, the portion of near infrared, optical and ultraviolet radiation produced by the stars that manages to bring it out into space, rather than hitting the dust around them. "It's basically the light of the stars that's gone everywhere," Ajello told Space.com. "All the light emitted by the stars able to escape into space basically becomes this background."

But extragalactic background light is difficult to measure because it is scattered very thinly in the universe and is eclipsed by bright light sources closer to the Earth. Thus, Ajello and his co-authors have tried to analyze this bright background by exploiting blazars – a type of galaxy that hides in its center a supermassive black hole that is projected to project a gigantic stream of high energy materials into our direction. Their data on these blazars and the high-energy gamma-ray photons they emit are provided by NASA's Fermi Gamma Space Telescope.

The study relies on an annoying feature of the blazars: some of the light at the highest energy that they produce bursts light particles of a much lower energy like the photons that we can see. This collision transforms a pair of incompatible photons into an electron and a positron, essentially removing the high-energy photon released by the blazar. "In a way, yes, it's a disadvantage if you focus solely on studies on blazar," Space Manasvita Joshi, an astrophysicist at Boston University, told Space.com. "But you can use it to your advantage for something like this."

The interaction between blazar photons and extragalactic background light photons only triggers at a specific energy level. This means that scientists can extrapolate from light produced at energy levels lower than what should have been produced at these higher energy levels. Then they can calculate the difference, which is what disappeared in the collisions. And from there, it is quite easy to cross the other side of the collision to measure extragalactic background light.

By studying many blazars – 739, to be precise – at different distances from the Earth, the team was able to identify changes in extragalactic background light over time. "By measuring the evolution of stellar light in the universe, you can actually turn that into a corresponding measure of star formation," Ajello said. "We discover exactly how this has changed over the history of the universe." [Messier’s List: Hubble Telescope’s Stunning Views of Deep-Sky Objects]

"Now the new thing is using this to understand the history of cosmic star formation," Joshi said. This is a question that scientists have long wanted to attack, but until now, they had to do it indirectly and rely on some initial assumptions, which is nonsmoking. is never ideal. "The problem [with previous estimates] Is it because your initial mass function is … it's really an estimate, it's an initial estimate, and this can introduce uncertainty, "Joshi said.

Thus, the fact that this different approach – bypassing these initial assumptions – draws some of the same conclusions regarding the formation of stars over time is comforting for astrophysicists, said Joshi. This not only validates these conclusions, but also suggests that scientists were on the right track with the initial assumptions they had introduced in the old methods of estimating star formation over time.

So, what is the most popular period for the birth of stars? About 10 billion years ago. And the proof is in their starlight.

The research is described in an article published November 29 in the journal Science.

Email Meghan Bartels at [email protected] or follow her. @meghanbartels. follow us @Spacedotcom and Facebook. Original article on Space.com.