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Astronomers have made an incredible discovery in what is known as our "cosmic dark ages." They have detected several overlapping bubbles of hydrogen gas that have been ionized by the stars in early galaxies.
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These galaxies existed when the Universe was merely 680 million years old, or less than 5% of its current age of 13.8 billion years. The finding constitutes the earliest direct evidence from the period when the first generation of stars formed, a period in the very early Universe known as the "cosmic dark ages."
At the time, no stars or galaxies existed yet to light up the Universe. We know of this period due to computer simulations but direct evidence is rare.
The very first stars of the Universe
Now, astronomers have revealed the imaging of a group of galaxies, known as EGS77, that contain the very first stars of the Universe. "The young Universe was filled with hydrogen atoms, which so attenuate ultraviolet light that they block our view of early galaxies," said James Rhoads at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
"EGS77 is the first galaxy group caught in the act of clearing out this cosmic fog."
EGS77 is visible due to the bubble that has been formed around it by hydrogen gas.
"Intense light from galaxies can ionize the surrounding hydrogen gas, forming bubbles that allow starlight to travel freely," said team leader Vithal Tilvi, a researcher at Arizona State University in Tempe.
"EGS77 has formed a large bubble that allows its light to travel to Earth without much attenuation. Eventually, bubbles like these grew around all galaxies and filled intergalactic space, clearing the way for light to travel across the Universe."
EGS77 was spotted as part of the Cosmic Deep And Wide Narrowband (Cosmic DAWN) survey. The ages of these galaxies were confirmed with spectra taken with the MOSFIRE spectrograph at the Keck I telescope at the W. M. Keck Observatory on Maunakea in Hawaii.