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New Spitzer and Hubble space telescope data show that in a few specific wavelengths of infrared light, some of the first galaxies to form in the Universe, less than a billion years after the Big Bang, were considerably brighter than predicted by astronomers.
The illustration of this artist shows what could look like one of the very first galaxies of the Universe. Image Credit: James Josephides, Swinburne Astronomy Productions.
Nobody knows for sure when the first stars of our universe come to life. But the evidence suggests that between about 100 and 200 million years after the Big Bang, the Universe was mostly filled with neutral hydrogen that may have begun to merge to form stars, which then began to form the stars. first galaxies.
About 1 billion years after the Big Bang, the Universe had become a glittering firmament. Something else has also changed: the electrons of neutral hydrogen, ubiquitous, have been eliminated by a process called ionization.
The era of reionization – the transition from the universe filled with neutral hydrogen to a universe filled with ionized hydrogen – is well documented.
Before this universe – wide transformation, long – wave light forms, such as radio waves and visible light, traversed the universe more or less without clutter. . But the shorter wavelengths of light – including ultraviolet light, X-rays, and gamma rays – have been interrupted by neutral hydrogen atoms. These collisions would strip the neutral hydrogen atoms of their electrons and ionize them.
But what could possibly have produced enough ionizing radiation to affect all the hydrogen in the universe? Was it individual stars? Giant galaxies?
If one or the other were the culprits, these first cosmic colonizers would have been different from most modern stars and galaxies, which usually do not release large amounts of ionizing radiation. Then again, maybe something else has completely caused the event, like quasars.
This deep-sky view of the sky, taken by NASA's Spitzer Space Telescope, is dominated by galaxies – some of them very faint and far away – surrounded by red. The inset on the bottom right shows one of these distant galaxies, made visible by Spitzer's long-term observation. The wide-field view also includes data from NASA / ESA's Hubble Space Telescope. Image Credit: NASA / JPL-Caltech / ESA / Spitzer / P. Oesch / S. De Barros / I. Labbe.
To go back to the time just before the end of the reionization era, NASA's Spitzer Space Telescope observed two regions of the sky for over 200 hours, allowing the telescope to capture the light that had traveled more than 13 billion years ago. Join us.
Among the longest scientific observations ever made by Spitzer, they were part of an observation campaign called "Spitzer's Large-Scale Treasury at the Time of the Re-ionization of Goods" (GREATS).
With the help of Spitzer observations and NASA / ESA's Hubble Space Telescope data, astronomer Stephane De Barros of the University of Geneva and his colleagues studied 135 distant galaxies.
The researchers found that these galaxies were all particularly bright in two specific wavelengths of infrared light produced by ionizing radiation interacting with the hydrogen and oxygen gases present in galaxies.
This implies that galaxies were dominated by massive young stars composed mainly of hydrogen and helium. They contain very small amounts of heavy elements – such as nitrogen, carbon, and oxygen – compared to stars found in modern galaxies.
These stars were not the first stars to form in the universe (these would have been composed only of hydrogen and helium) but still belonged to a very first generation of 39, stars.
The era of reionization was not an instant event. Therefore, although the new results are not enough to close the book on this cosmic event, they provide new details on how the universe evolved at that time and on the transition.
"These results from Spitzer are certainly another step in solving the mystery of cosmic reionization," said Dr. Pascal Oesch, a member of the team, also from the University of Geneva.
"We now know that the physical conditions in these early galaxies were very different from those of the typical galaxies of today."
The results were published in the Monthly Notices from the Royal Astronomical Society.
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S. De Barros et al. GREATS Hβ +[O III]Brightness function and galaxy properties in z~8: Browse the path of JWST. MNRAS, published online April 4, 2019; doi: 10.1093 / mnras / stz940
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