A new analysis of the early universe sheds new light on the "cosmic dawn" of the universe

Peering far back into the cosmic dawn

The scientists were actually able to place these limits, in part, since they didn't find what they were looking for. The researchers had set out to observe the 21-centimeter hydrogen line. The absence of the hydrogen line allowed them to rule out certain scenarios, including galaxies that were inefficient at cosmic heating gas and ineffective at producing radio emissions.

"We were looking for a signal with a certain amplitude,” explained Harry Bevins, a Ph.D. student from Cambridge's Cavendish Laboratory and the paper's lead author. "But by not finding that signal, we can put a limit on its depth. That, in turn, begins to inform us about how bright the first galaxies were."

Though our technology today doesn't give us the capacity to directly observe such early galaxies, the new findings, reported in a study in the journal Nature Astronomy, provide vital clues about the early evolution of the cosmos. They also serve as a guide for future projects that will be able to peer further back in time. The SKA project, for example, will use two next-generation telescopes by the end of the decade to take images from the early universe by peering further than ever before.

Today, astronomers use data from existing telescopes to try to detect the cosmological signal of the first stars re-radiated by thick hydrogen clouds. This radio signal, known as the 21-centimeter line, is produced by hydrogen atoms from the early universe. Observations can allow scientists to better understand galaxies from further back in time than NASA's James Webb Space Telescope can observe.

Uncovering the mysteries of the early universe

The Cambridge-led international team's analysis of the SARAS3 data was the first time that radio observations of the averaged 21-centimeter line have provided insight into the properties of the first galaxies by enabling scientists to determine specific limits of their physical properties.

"Our analysis showed that the hydrogen signal can inform us about the population of first stars and galaxies," said co-lead author Dr. Anastasia Fialkov from Cambridge's Institute of Astronomy. "Our analysis places limits on some of the key properties of the first sources of light, including the masses of the earliest galaxies and the efficiency with which these galaxies can form stars. We also address the question of how efficiently these sources emit X-ray, radio, and ultraviolet radiation."

The scientists' findings are an early step and aim to gradually uncover the mysteries of the early universe currently shrouded in figurative and literal darkness. “This is an early step for us in what we hope will be a decade of discoveries about how the Universe transitioned from darkness and emptiness to the complex realm of stars, galaxies, and other celestial objects we can see from Earth today,” said Dr. Eloy de Lera Acedo from Cambridge's Cavendish Laboratory, who co-led the research.