Using data from the NASA’s Fermi gamma-ray telescope, scientists calculated the number of all photons ever existing in the universe, which will help reveal the history of star formation and ultimately get to the Big Bang.
From the data collected by the Fermi telescope, we were able to measure the total amount of starlight that has ever occurred. This allowed us to better understand the evolution of stars and get fascinating information about how the Universe spawned its radiant contents.
-Marco Agello, lead author of the study from Clemson University (USA)
It is believed that the formation of the first stars began several hundred million years after the Big Bang. Now in the observable universe about two trillions of galaxies and trillions of trillions of stars are recorded. According to the new dimension, the number of photons (particles of visible light) released into space by stars is estimated at 1084^4. Or in other words: 4,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 photons.
Despite the huge amount, it is interesting to note that, with the exception of the light coming from the Sun and the Milky Way, the rest of the starlight reaching the Earth is extremely dim and equivalent to a 60-watt light bulb, visible in total darkness from a distance of 2.5 kilometers. That is why the night sky for the naked eye is so dark.
Space Fermi telescope in June 2018 celebrated its 10th anniversary. During this time, a powerful observatory has provided a huge amount of data on gamma rays and their interaction with the extragalactic background (EBL), which is a cosmic mist consisting of all ultraviolet, visible and infrared light emitted by stars or dust in their vicinity. Scientists have analyzed almost nine years of data on gamma radiation signals of 739 blazars.
Blazars are galaxies containing supermassive black holes that are capable of emitting jets of energy particles almost at the speed of light. The gamma quanta generated inside the jets eventually collide with the cosmic mist, leaving an observable imprint. This allowed the team to measure the density of fog not only in a particular place, but also at a specific point in time in the history of the Universe.
Gamma photons flying through the fog of starlight have a high probability of absorption. Measuring how many photons were absorbed, the scientists determined how thick the fog was, and also measured as a function of time, how much light was in the entire wavelength range.
The problem of distant galaxies
One of the obstacles faced by previous studies of the history of star formation in the Universe was that some galaxies are too far or too weak to be accessible to modern telescopes. The team managed to get around this using Fermi data to analyze the extragalactic background.
Starlight, elusive from even the most distant galaxies, ultimately becomes part of the EBL. Therefore, accurate measurements of this cosmic fog, which have only recently become possible, have eliminated the need to estimate the emission of light from ultra-distant galaxies.
Using blazars at different distances from us, we measured the total starlight in different periods of time. We received the total starlight of each era – one, two, six billion years ago and so on – right up to the formation of the first stars, which allowed us to reconstruct the EBL and determine the star formation history in the Universe in the most efficient way.
-Vaidehi Paliya, co-author from Clemson University
When high-energy gamma rays collide with low-energy visible light, they turn into pairs of electrons and positrons. Fermi’s ability to detect gamma rays in a wide range of energies makes it unique for the mapping of cosmic fog.
Scientists have long tried to measure EBL. However, very bright objects in the solar system made it irresistibly difficult. Our equipment is insensitive to the nearest light and thus copes with these difficulties.
-Abhishek Desai, co-author of the study at Clemson University
Star formation, which occurs during the collapse of dense regions of molecular clouds, reached its peak about 11 billion years ago. But although the birth of new stars has slowed down since then, it never stopped.
Star formation is a great space conveyor and a utilizer of energy, matter and metals. This is the engine of the universe. Without the evolution of stars, we would not have the fundamental elements necessary for life to exist.
-Dieter Hartmann, a member of the research team at Clemson University
Understanding star formation also has implications for other areas of astronomy, including studies of cosmic dust, evolution of galaxies, and dark matter. Team analysis will provide future missions, in particular, the NASA “James Webb” space telescope, with material for studying the early evolution of stars.
The first billions of years of the history of the Universe is a very interesting era, which has not yet been explored by modern instruments. Our dimension allows you to look into the depths of the ages. Perhaps one day we will find a way to return to the Big Bang. This is our ultimate goal.
-Marco Agello
Scientists have calculated the whole light in the universe
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