New clues into way ancient galaxies lit up Universe

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GENEVA

Researchers report on observations of some of the first galaxies to form in the universe, less than 1 billion years after the big bang (or a little more than 13 billion years ago). The data show that in a few specific wavelengths of infrared light, the galaxies are considerably brighter than scientists anticipated. The study is the first to confirm this phenomenon for a large sampling of galaxies from this period, showing that these were not special cases of excessive brightness, but that even average galaxies present at that time were much brighter in these wavelengths than galaxies we see today.

No one knows for sure when the first stars in our universe burst to life. But evidence suggests that between about 100 million and 200 million years after the Big Bang, the Universe was filled mostly with neutral hydrogen gas that had perhaps just begun to coalesce into stars, which then began to form the first galaxies.

By about 1 billion years after the big bang, the Universe had become a sparkling firmament. Something else had changed, too: Electrons of the omnipresent neutral hydrogen gas had been stripped away in a process known as ionisation. The Epoch of Reionisation — the changeover from a universe full of neutral hydrogen to one filled with ionised hydrogen — is well documented.

Before this Universe-wide transformation, long-wavelength forms of light, such as radio waves and visible light, traversed the universe more or less unencumbered. But shorter wavelengths of light — including ultraviolet light, X-rays and gamma rays — were stopped short by neutral hydrogen atoms. — VoM

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