The Cosmic Dark Age
After the Big Bang, the universe was a dark sea of hydrogen and helium gas. For about 180 million years, this "Cosmic Dark Age" persisted until gravity slowly pulled the primordial gas into dense clumps. Inside these clumps, the first stars ignited, ending the darkness and beginning an era called the "Cosmic Dawn". These were not like any stars that exist today. Known as Population III stars, they were formed from pure hydrogen and helium, the only elements forged in the Big Bang.
The absence of heavier elements—which astronomers call "metals"—allowed these stars to grow to incredible sizes, possibly hundreds or even up to 1,000 times the mass of our Sun. Their immense mass made them hot and luminous, with a blue or ultraviolet light. It also meant they had very short lives. They burned through their nuclear fuel in just a few million years before dying in spectacular explosions. Some of these deaths were pair-instability supernovae, explosions so violent they completely obliterated the star, leaving no black hole or neutron star behind. These explosions scattered the first heavy elements, like carbon and oxygen, into the cosmos, enriching the gas clouds that would form the next generations of stars, Population II and I.
The Hunt for an Echo
Directly observing a Population III star is likely impossible; they are all long gone. Instead, astronomers hunt for their fossil record—the signature they left on the hydrogen that filled the early universe. Neutral hydrogen atoms naturally absorb and emit radio waves with a wavelength of 21 centimeters. The intense ultraviolet light from the first stars would have affected this signal, creating a distinct absorption dip in the cosmic radio background. This ancient signal, stretched by the expansion of the universe to a wavelength of several meters, astronomers are searching for today.
This POI's coordinates point to the Murchison Radio-astronomy Observatory (MRO) in Western Australia, one of the most radio-quiet places on Earth. It is an ideal location for listening to the faintest whispers from the early cosmos. Here, an experiment called EDGES (Experiment to Detect the Global EoR Signature) detected a potential signal from this era in 2018. While the signal was deeper than predicted, sparking intense scientific debate, it showed more about the Cosmic Dawn.
The MRO also houses precursor telescopes for the Square Kilometre Array (SKA), a next-generation observatory. The low-frequency part of the SKA, SKA-Low, will consist of over 131,000 antennas spread across the desert and is designed specifically to map the 21-cm signal from the early universe in unprecedented detail. In parallel, the James Webb Space Telescope (JWST) searches for indirect evidence by observing extremely distant galaxies that might contain clusters of these first-generation stars.