Los Angeles, California – In the early stages of the universe, there was a period known as the “cosmic dark ages,” occurring before the formation of stars and galaxies. During this time, the lack of bright sources made it challenging for astronomers to observe the cosmos.
One key element present during this period was neutral hydrogen, the most abundant element in the universe. Unlike today, where most hydrogen exists in a super-heated plasma state, the early universe’s hydrogen was cool and neutral.
Neutral hydrogen consists of a proton and an electron, each possessing a quantum property called spin. When the electron’s spin randomly flips, the hydrogen emits energy in the form of a 21-centimeter wavelength photon. Despite these quantum transitions being rare, the presence of enough neutral hydrogen allows for the creation of a significant signal.
Observations of 21-cm radiation have been instrumental in astronomy, helping to map cold gas reservoirs within the Milky Way. The emission of 21-cm radiation from primordial neutral hydrogen clouds during the cosmic dark ages sheds light on this ancient era, with the radiation traveling over 13 billion light-years before reaching telescopes and experiencing the redshift effects of the expanding universe.
Overall, the study of neutral hydrogen and 21-cm radiation offers valuable insights into the early universe’s evolution and the processes that occurred before the emergence of stars and galaxies. Through these observations, astronomers can piece together the cosmic history leading up to the universe’s current state.