Some newly discovered distant galaxies are helping astronomers shine a light on the time when the early Universe moved out of the cosmic dark ages and began to glow.
Following the Big Bang, 13.8 billion years ago, it took hundreds of thousands of years for the first complete atoms to form. But the Universe was completely opaque and hundreds of million more years had to pass before stars and galaxies formed and began to shine.
This “switching on” of the Universe is known in science as the “epoch of reionisation”. A boost to our understanding of the period is expected to follow the identification of a fantastic family of remote galaxies.
The first example of a spectacularly bright galaxy as seen during the epoch of reionisation was made in 2015 by a team led by Dr David Sobral, of Lancaster University. It was dubbed CR7 – short for Cosmos Redshift 7 to denote its distance – and it was thought to be home to the earliest stars to form.
The same team also found another similar galaxy, called MASOSA, and a further example, named Himiko, was discovered by a Japanese team. These finds all hinted at the existence of a larger population of similar galaxies, which might contain the earliest stars and black holes.
Sobral’s team has now discovered more examples of these first galaxies, using giant telescopes in Hawaii and Chile, and observed that they are all enclosed in a giant bubble of ionised gas.
Five bright sources have now been confirmed, but they are thought to be just a handful amongst hundreds of thousands of a similar age, waiting to be discovered.
Announcing the discoveries at the UK’s National Astronomy Meeting in Nottingham, Sobral said in a statement: “Stars and black holes in the earliest, brightest galaxies must have pumped out so much ultraviolet light that they quickly broke up hydrogen atoms in the surrounding universe. The fainter galaxies seem to have stayed shrouded from view for a lot longer. Even when they eventually become visible, they show evidence of plenty of opaque material still in place around them.”