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Astrophysicist Marco Ajello at Clemson Outdoor Lab. (Credit: Pete Martin / Clemson University)
Astrophysicists estimate that our universe was formed about 13.7 billion years ago. The first stars were formed while it was only a few hundred million years ago. In scrutinizing the early days of stellar creation, scientists from South Carolina measured all the light of the stars ever produced during the entire history of the observable universe.
Scientists have been working for a long time to obtain this measurement, also called extragalactic background light (EBL) or "cosmic fog". "The EBL represents the book chronicling the history of stellar activity and the evolution of galaxies in the universe," said Marco Ajello, principal investigator and astrophysicist at Clemson College of Science in South Carolina, in an email.
Measuring EBL could be a great tool for scientists, helping them better understand the evolution of galaxies, star formation processes, and how the universe has evolved, Ajello explained. But so far scientists have not been able to take this step because EBL is much darker than the Milky Way and other night sky lights. Scientists were not able to observe distant galaxies because their too dark and brighter light in the foreground further obscured this view. Now, using an indirect method, the scientists finally made this step.
The team found that the amount of stellar light, or the number of photons (visible light particles) emitted by the stars during the history of the observable universe, was 4 × 10 ^ 84 photons. Or, alternatively, 4,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,
1,000,000,000,000,000,000,000,000 of photons.
An indirect measure
The team was able to perform this stellar measurement by observing blazars or galaxies with supermassive black holes emitting beams of matter and radiation in our direction, using NASA's Fermi Gamma space telescope.
"Using blazars at different distances from us, we measured total starlight at different times. We measured the total starlight of each era – a billion years ago, two billion years ago, six billion years ago, and so on. – since the creation of the stars. This allowed us to rebuild the EBL and determine the history of star formation in the universe more efficiently than before, "said Vaidehi Paliya, co-author and postdoctoral fellow having analyzed nearly nine years of relevant data. A declaration.
Blazars emit jets of energetic particles containing gamma rays or ultra-energetic photons. And the gamma rays emitted by the blazars cross the cosmic fog (EBL), consisting of visible and ultraviolet light. When gamma rays collide with visible light, they transform into pairs of electrons and positrons. "In fact, the process attenuates the gamma-ray signal in the same way that the fog darkens a distant lighthouse," NASA said in a press release on the phenomenon. These collisions leave visible footprints that scientists can observe with Fermi.
"By measuring the number of photons absorbed, we were able to measure the thickness of the fog and also, as a function of time, the amount of light available throughout the entire range of wavelengths," Ajello said. its press release.
By mapping the various densities of this cosmic fog, researchers were able to observe an extremely distant (and therefore extremely old) starlight, since these collisions occur over great distances. This technique has also worked because, by indirectly observing the light of the stars through interactions between gamma rays and visible light, the technique is not masked or hindered by a bright light in the foreground.
"The first billions of years of our universe's history are a very interesting time that the current satellites have not yet investigated. Our measurement allows us to take a look at the inside. Maybe one day we will find a way to go back to the Big Bang. This is our ultimate goal, "Ajello concluded in his statement.
The researchers published their work today in the journal Science.
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