Astronomers have detected the glow from the time when the earliest stars began to shine, 180 million years after the Big Bang.
These latest observations, made by the Experiment to Detect the Global Epoch of Reionisation Signature (EDGES) project, couldn’t pick up the light from these stars directly: even the most powerful telescopes can only pick up light from galaxies that existed 400 million years after the Big Bang.
Instead the team searched for the imprint that the star’s bright ultraviolet light left on the cosmic background radiation.
The ultraviolet radiation from early stars interacted with surrounding hydrogen molecules, causing them to absorb the photons that make up the cosmic microwave background radiation (CMB).
“You start seeing the hydrogen gas in silhouette at particular radio frequencies,” says Alan Rodgers from MIT’s Haystack Observatory, who took part in the study.
“This is the first real signal that stars are starting to form, and starting to affect the medium around them.”
This interaction between stars and hydrogen eventually led to the hydrogen atoms of the Universe being torn apart and stripped of their electrons; an era known as ‘reionisation’.
The ‘dip’ in radio frequency from this early light has been difficult to find as it sits between 65 and 95 megahertz.
Not only is this one of the most widely used FM frequencies, it is also the wavelengths that the Milky Way galaxy naturally transmits.
“There is a great technical challenge to making this detection. Sources of noise can be 10,000 times brighter than the signal – it’s like being in the middle of a hurricane and trying to hear the flap of a hummingbird’s wing,” says Peter Kurczynski from the National Science Foundation who oversaw the funding for the project.
The signal the team did find was twice as intense as those predicted by models.
Several theories have been put forward to explain this, including the idea that dark matter interactions might be at work.
“If that idea is confirmed, then we’ve learned something new and fundamental about the mysterious dark matter that makes up 85 per cent of the matter in the Universe, ” says Judd Bowman from the University of Arizona who led the project.
“This would provide the first glimpse of physics beyond the standard model.”