Scientists delighted as failure to detect key signal from space explains the beginnings of the universe

Scientists have failed to detect a key signal from space – and used it to explain some of the earliest parts of the universe.

The inability to pick up the signal has allowed researchers to better understand the first galaxies to exist. It is one of the first times they have been able to study the period known as the “cosmic dawn”, when the first stars and galaxies came into being.

Scientists are now able to place limits on the mass and energy coming out of those first stars and galaxies – using a counterintuitive method.

Researchers were looking for a specific signal, known as the 21-centimetre hydrogen line. After they didn’t find it, they were able to rule out some scenarios for the beginnings of the universe’s stars and galaxies.

Those galaxies cannot yet be seen directly. But the new study is a way of understanding one of the most important moments in the cosmos, when it switched from being largely empty to being full of stars.

The 21-centimetre hydrogen line is a radio signal that is produced by hydrogen atoms in the early universe. Scientists are able to use it to examine entirely populations of very early galaxies.

At some point, scientists hope to see the earliest light from those first galaxies. And in 2018, researchers published a study that suggested they had – but found that the signal was much stronger than expected, and the conclusions remain in dispute.

In the new study, researchers used India’s SARAS3 radio telescope to try and find a scenario that could explain why that signal was so bright. But they could not find an explanation for it.

In failing to detect it, however, that allowed the researchers to understand the galaxies they were looking for in the first place. It also suggests that the dramatic implications of that 2018 finding – that something very unexpected was going on in the early universe – is not the case, and scientists can go back to working on more conventional scenarios.

“We were looking for a signal with a certain amplitude,” said Harry Bevins, a PhD 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.”

Scientists hope that the research is the beginning of a new era of developments in our understanding of the cosmic dawn and the beginnings of the universe. Nasa’s new JWST, for instance, will be able to directly see individual galaxies in the early universe.

“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, in a statement.

The study is described in a paper, ‘Astrophysical constraints from the SARAS 3 non-detection of the cosmic dawn sky-averaged 21-cm signal’, published in Nature Astronomy today.