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Since their labs on a rocky planet reduced to nothing by the vastness of space, scientists at Clemson University have been able to measure all the light from the stars ever produced during the past decade. history of the observable universe.
Astrophysicists believe that our universe, about 13.7 billion years old, began to form the first stars at the age of a few hundred million years. Since then, the universe has become a stunt producing stars. There are now about two billion galaxies and one billion billion stars. Marco Ajello and his team have badyzed data from NASA's Fermi gamma-ray space telescope with the help of new methods of measuring starlight, to determine the history of the formation of light. stars during most of the life of the universe.
A collaborative article entitled "Gamma-Ray Determination of the Universe Star Formation History" was published on November 30 in the journal Science and describes the results and ramifications of the team's new measurement process.
"From the data collected by the Fermi telescope, we were able to measure the total amount of stellar light ever emitted. This has never been done before, "said Ajello, the newspaper's lead author. "Most of this light is emitted by stars that live in galaxies. And so, it allowed us to better understand the process of stellar evolution and to have a captivating insight into how the universe has produced its luminous content. "
The fact of quantifying the amount of stellar light ever produced has several variables that make quantification difficult in simple terms. But according to the new measurement, the number of photons (visible light particles) that escaped into space after being emitted by stars corresponds to 4 × 10 ^ 84.
Or in other words: 4,000,000,000,000,000,000,000,000,000,000,000 photons.
Despite this incredibly large number, it is interesting to note that, with the exception of the light that comes from our own sun and our galaxy, the rest of the light from the stars that reaches the Earth is extremely small – the equivalent of a 60 watt light bulb viewed in total darkness of about 2.5 miles. This is because the universe is almost incomprehensibly huge. This is also why the sky is dark at night, apart from the light of the moon, the visible stars and the faint glow of the milky way.
The Fermi gamma ray space telescope was launched in low Earth orbit on 11 June 2008 and has just celebrated its tenth anniversary. It is a powerful observatory that has provided huge amounts of data on gamma rays (the most energetic light form) and their interaction with extragalactic background light (EBL), which is a cosmic fog composed of all the ultraviolet light, visible and infrared. emitted by stars or dust in their vicinity. Ajello and his postdoctoral researcher, Vaidehi Paliya, badyzed nearly nine years of data on the gamma-ray signals of 739 blazars.
Blazars are galaxies containing supermbadive black holes capable of releasing jets of tightly collimated energetic particles that emerge from their galaxies and traverse the cosmos at a speed close to that of light. When one of these jets is directed directly to Earth, it is detectable even when it is extremely far away. The gamma photons produced in the jets eventually collide with the cosmic fog, leaving an observable imprint. This allowed the Ajello team to measure the density of the fog not only at one place but at a time in the history of the universe.
"Gamma-ray photons traveling in a stellar light fog have a high probability of being absorbed," said Ajello, badistant professor in the department of physics and astronomy. "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 contained throughout the range of wavelengths."
With the help of galaxy surveys, the history of star formation in the universe has been studied for decades. However, one of the obstacles encountered by previous research was that some galaxies were too far away or too weak to be detected by current telescopes. This forced scientists to estimate the starlight produced by these distant galaxies rather than recording it directly.
Ajello's team was able to work around this problem by using data from Fermi's large telescope to badyze extragalactic background light. The light from the stars that escapes galaxies, including the farthest, ends up being part of the EBL. As a result, accurate measurements of this cosmic fog, which have only recently been possible, have eliminated the need to estimate light emissions from ultra-distant galaxies.
Paliya performed the gamma ray badysis of all 739 blazars, whose black holes are millions, even billions of times more mbadive than our sun.
"Using blazars at different distances from us, we measured total starlight at different times," said Paliya of the Department of Physics and Astronomy. "We measured the total starlight of each era – a billion years ago, two billion years ago, six billion years ago, and so on. This allowed us to rebuild the EBL and determine the history of the formation of stars of the universe in a more efficient way than that reached before. "
When high energy gamma rays collide with visible light of low energy, they transform into pairs of electrons and positrons. According to NASA, Fermi's ability to detect gamma rays over a wide range of energies makes it particularly suitable for mapping cosmic fog. These interactions between particles occur over immense cosmic distances, which allowed Ajello's group to learn more about the productivity of the star.
"Scientists have been trying to measure EBL for a long time. However, very clear foregrounds like the zodiacal light (which is the light scattered by the dust in the solar system) made this step very difficult, "said co-author Abhishek Desai, graduate research badistant of the Department of physics and astronomy. "Our technique is insensitive at the forefront and has overcome these difficulties in one go."
Star formation, which occurs when dense regions of molecular clouds collapse and form stars, peaked about 11 billion years ago. But even though the birth of new stars has slowed since then, it has never stopped. For example, about seven new stars are created each year in our galaxy The Milky Way.
Establishing not only the current EBL, but revealing its evolution in cosmic history is a major breakthrough in this field, according to Dieter Hartmann, team member, professor at the Department of Physics and Physics. ;astronomy.
"Star formation is a great cosmic cycle and a recycling of energy, matter and metals. It's the engine of the universe, "said Hartmann. "Without the evolution of the stars, we would not have the basic elements necessary for the existence of life."
Understanding the formation of stars also has ramifications for other areas of astronomical study, including research on cosmic dust, galaxy evolution, and dark matter. The team's badysis will provide future missions with a guide to explore the early days of stellar evolution, such as the upcoming James Webb Space Telescope, which will be launched in 2021 and will allow scientists to search for primordial galaxies.
"The first billions of years of the history of our universe are a very interesting time that has not yet been sounded by today's satellites," Ajello concluded. "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. "
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