Faintest Galaxy discovered by scientists

The faintest galaxy from the early universe has been discovered by a team of scientists.
The galaxy, hidden behind a galaxy cluster known as MACS2129.4-741, was detected "as it was 13 billion years ago".

The results of the study, which have been published in Astrophysical Journal Letters, could help explain how a period called the "cosmic dark ages" ended – a period in which the temperature of cosmic radiation cooled dramatically, from 400 kelvin to around 60.

This cooling happened as the universe expanded, according to the big bang theory. This allowed for the possibility of water – potentially leading to primitive life.

During this time, according to Tommaso Treu, professor of physics at UCLA and co-author of the research, "protons captured electrons to form hydrogen atoms – giving rise to the cosmic dark ages".

"At some point, a few hundred million years later, the first stars formed and they started to produce ultraviolet light capable of ionizing hydrogen," he said. "Eventually, when there were enough stars, they might have been able to ionize all of the intergalactic hydrogen and create the universe as we see it now."

The team discovered the galaxy using "gravitational lensing" – a theory predicted by Einstein – which projects a distorted image similar to that of an image behind a glass lens.

The process of cooling has so far been a mystery to scientists, who were unsure whether it was caused by stars becoming visible or from gas falling into supermassive black holes.

"Currently, the most likely suspect is stars within faint galaxies that are too faint to see with our telescopes without gravitational lensing magnification," said Treu. "This study exploits gravitational lensing to demonstrate that such galaxies exist, and is thus an important step toward solving this mystery."

"This galaxy is exciting because the team infers a very low stellar mass, or only one per cent of one per cent of the Milky Way galaxy," said Marc Kassis, staff astronomer at the Keck Observatory.

"It's a very, very small galaxy and at such a great distance, it's a clue in answering one of the fundamental questions astronomy is trying to understand: What is causing the hydrogen gas at the very beginning of the universe to go from neutral to ionized about 13 billion years ago?" said Kassis. "That's when stars turned on and matter became more complex."

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