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Scientists using data from NASA's Fermi gamma-ray space telescope have measured all the starlight produced at over 90% of the universe's history.
The analysis, which examines the gamma-ray output of distant galaxies, estimates the rate of star formation and is a reference for future missions exploring the still obscure beginnings of stellar evolution.
"Stars create most of the light we see and synthesize most of the heavy elements of the universe, such as silicon and iron," said lead scientist Marco Ajello, an astrophysicist at Clemson University in Carolina. from South. "Understanding how the cosmos in which we live is born largely depends on understanding the evolution of the stars."
An article describing the new Starlight measurement appears in the November 30 issue of Science and is now available online.
One of the main goals of the Fermi mission, which celebrated its 10th anniversary in orbit this year, was to evaluate the extragalactic background light (EBL), a cosmic fog composed of all the ultraviolet light stars , visible and infrared created above the story. As the light of the stars continues to travel in the cosmos long after its sources have become extinct, the EBL measurement allows astronomers to study the formation and evolution of stars separately from the stars themselves.
"This is an independent confirmation of past measurements of star formation rates," said David Thompson, deputy scientist of the Fermi Project at NASA's Goddard Space Flight Center in Greenbelt, in Maryland. "In astronomy, when two completely independent methods give the same answer, it usually means that we are doing something right, in which case we measure star formation without looking at them, but observing the gamma rays that have crossed the cosmos. . "
Gamma rays are the form of light at the highest energy. In fact, they are so energetic that their interactions with starlight have unusual consequences. "When the right light frequencies collide, they can turn into matter thanks to Albert Einstein's famous E = mc2 equation," said co-author Alberto Dominguez, astrophysicist at the Complutense University. from Madrid.
The collision between a high-energy gamma ray and infrared light, for example, transforms energy into a pair of particles, an electron, and its antimatter counterpart, a positron. The same process occurs when medium energy gamma rays interact with visible light and low energy gamma rays interact with ultraviolet light. Fermi's ability to detect gamma rays over a wide range of energies makes it particularly suitable for mapping the EBL spectrum. Enough of these interactions occur over cosmic distances that scientists observe further in the past, plus their effects become apparent on gamma ray sources, allowing deep probing of the stellar content of the universe.
Scientists, led by Vaidehi Paliya, a postdoctoral researcher from the Ajello group in Clemson, examined the gamma-ray signals of 739 blazars – galaxies with monstrous black holes – collected over a nine-year period by the Fermi Large Area Telescope (LAT) . The measure, quintupled by the number of blazars used in a previous EBL Fermi analysis released in 2012, includes new calculations on how EBL is built over time, thus revealing the peak of star formation there. about 10 billion years ago.
The new EBL measurement also provides important confirmation of previous estimates of star formation from missions analyzing many individual sources in deep galaxy surveys, such as the Hubble Space Telescope. However, these types of surveys often lack stars and weaker galaxies and can not explain the formation of stars that takes place in the intergalactic space. These missing contributions must be estimated when analyzing each survey.
EBL, however, includes starlight from all sources and avoids these problems. The result of Fermi thus provides independent confirmation that measurements using surveys in deep galaxies correctly account for their biases. It can also help guide future mission investigations such as the James Webb Space Telescope (JWST).
"One of the main goals of Webb is to understand what has happened over the first billion years after the big bang," said co-author, Kári Helgason, astrophysicist at the University of Iceland. "Our work imposes significant new limits to the amount of starlight we can expect to see in this first billion years – a largely unexplored period in the universe – and is a point of reference for future studies. "
Reference:
"Gamma ray determination of the history of star formation in the universe," Fermi-LAT Collaboration, November 30, 2018, Science [http://science.sciencemag.org/content/362/6418/1031, related perspective: http://science.sciencemag.org/content/362/6418/995].
The Fermi Gamma Ray Space Telescope is an astrophysics and particle physics partnership run by NASA's Goddard Space Flight Center in the Maryland Greenbelt. Fermi was developed in collaboration with the US Department of Energy, with significant contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.
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