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Why scientists tried to measure all the bright starlight



Fermi-LAT view of the gamma-ray sky.
Image: Fermi-LAT

Astronomers announced this week that they wanted to measure all starlight in the universe.

You may wonder why. Ultimately, they try to tell the story of the universe.

"We wanted to know how the history of star formation works," said Kari Helgason, a scientist at the Max Planck Institute for Astrophysics in Germany, to Gizmodo.

The entire universe is diffuse with "extragalactic background light" or EBL, photons emitted by all galaxy stars in infrared, optical and ultraviolet wavelengths. Back in time, this light is the sum of all the light emitted by the stars from the Big Bang to the moment and the distance you are looking at. Remember that the distance is the same as the time in the room, so look at another area of ​​the room, you see fewer stars. The EBL can weaken gamma rays. So the scientists have measured the gamma rays coming from far away quasars to see if they bear the signature of a shadow from that starlight. With this information, scientists can make a statement about the speed of star formation over time .

The researchers analyzed nine-year gamma rays collected from the Fermi Gamma-Ray Space Telescope. Specifically, they viewed 739 blazars, black holes ejecting matter-directed matter beams, and a gamma-ray burst. These objects went back 200 million to 1

1.6 billion years. They applied an equation to all data that calculated the total background light, according to the new study published in Science.

The results were consistent with earlier extragalactic background light measurements, indicating that star formation reached its maximum about 10 billion years ago.

The extragalactic background light is exciting for other reasons, Elisa Prandini, astroparticle physicist at the University of Padua in Italy, wrote in a commentary for Science. The measurement limits the number of weak galaxies around 12 billion years ago. These galaxies are thought to have caused a "reionization time", an important time in the history of the universe, when the first atoms were formed from protons that combine with electrons, and the energy of the new galaxies split them. However, very few sources were used for this specific measurement, so further observations of distant gamma-ray sources could clarify things.

In addition, the extragalactic backlight could provide a new way to never hunt. Previously seen particles, said Prandini.

The study has reservations, Helgason said – assuming that all background light came from starlight, but strong black holes can spew radiation into space. Current estimates suggest that they do not make much of an impact, but it's worth taking a closer look.

No, you do not just add the starlight of the universe for free.

[Science]


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