We finally know what turned the lights on at the dawn of time
We finally know what brought light to the dark and formless void of the early Universe.
According to data from the Hubble and James Webb Space Telescopes, the origins of the free-flying photons in the early cosmic dawn were small dwarf galaxies that flared to life, clearing the fog of murky hydrogen that filled intergalactic space.
“This discovery unveils the crucial role played by ultra-faint galaxies in the early Universe’s evolution,” says astrophysicist Iryna Chemerynska of the Institut d’Astrophysique de Paris.
“They produce ionizing photons that transform neutral hydrogen into ionized plasma during cosmic reionization. It highlights the importance of understanding low-mass galaxies in shaping the Universe’s history.”
At the beginning of the Universe, within minutes of the Big Bang, space was filled with a hot, dense fog of ionized plasma. What little light there was wouldn’t have penetrated this fog; photons would simply have scattered off the free electrons floating around, effectively making the Universe dark.
As the Universe cooled, after about 300,000 years, protons and electrons began to come together to form neutral hydrogen (and a little bit of helium) gas. Most wavelengths of light could penetrate this neutral medium, but there was very little in the way of light sources to produce it. But from this hydrogen and helium, the first stars were born.
Those first stars delivered radiation that was strong enough to peel electrons away from their nuclei and reionize the gas. By this point, however, the Universe had expanded so much that the gas was diffuse, and could not prevent light from shining out. By about 1 billion years after the Big Bang, the end of the period known as the cosmic dawn, the Universe was entirely reionized. Ta-da! The lights were on. [Continue reading…]