For 100s of millions of years after the Big Bang, the entire universe was a thick soup of hydrogen atoms swimming in total blackness. So dense was this cosmic goulash that the first light from the first stars in existence couldn’t penetrate it — the hydrogen fog simply absorbed and scattered the starlight in circles, trapping the universe in a cosmic dark age as ever more stars, galaxies and black holes slowly smoldered to life. That all changed after 500 ma, when a grand cosmic makeover called the epoch of reionization began. As ancient galaxies grew ever larger and radiated more powerful energy, they began to burn away the cosmic fog that surrounded them by ionizing hydrogen atoms into a plasma of free protons and electrons. Suddenly, light could travel across the cosmos — first through “bubbles” of plasma surrounding large galaxies, then farther and farther as multiple bubbles began to expand and overlap. The galaxy group, named EGS77, dates to 680 ma after the Big Bang and appears to be surrounded by 3 overlapping bubbles of plasma — meaning these pioneering galaxies may have been caught in the act of reionizing their corner of the universe and bringing the cosmic dark ages to an end.

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