Using the James Webb Space Telescope (JWST), an international team of astronomers has found compelling evidence that early galaxies were responsible for the reionization of the early universe. This is the process by which neutral hydrogen atoms are ionized, making the universe transparent to light at wavelengths that would have been absorbed by the atoms. The research was done by members of the EIGER collaboration, which is using the JWST’s Near Infrared Camera (NIRCam) to study light from quasars in the early universe.
The cosmological era of reionization occurred around a billion years after the Big Bang. Prior to reionization, neutral hydrogen gas between early galaxies absorbed light at certain wavelengths. Then something caused the cosmos to heat up, ionizing the gas to create a plasma. These regions of plasma were less efficient at absorbing light, creating “bubbles” of transparency in the universe.
These bubbles were much larger than the galaxies themselves, with diameters of about 4 million light–years across. Over the hundred million years or so, the bubbles grew and joined together, and eventually the entire universe became transparent. However, exactly what caused this reionization is an important cosmological mystery.
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