Faintest early-universe galaxy discovered

Scientists have detected and confirmed the faintest early-universe galaxy yet, located about 13 billion light years away from Earth.
This new object could help astronomers understand the "reionisation epoch" when the first stars became visible.
Gravitational lensing and a special instrument on the 10-meter telescope at the W M Keck Observatory in Hawaii, enabled the team to see the incredibly faint object.
It would not have been visible at all if the light from the galaxy was not magnified by the gravitational lens, said Kuang-Han Huang, postdoctoral researcher at University of California, Davis.
Gravitational lensing is a phenomenon predicted by Einstein. Because gravity can bend the path of light, it is possible for a distant galaxy to be magnified through the "lens" created by the gravity of another object between it and the viewer.

In this case, the detected galaxy was behind the galaxy cluster MACS2129.4-0741, which is massive enough to create three different images of the object.

The astronomers were able to show that the three images were of the same galaxy because they showed similar spectra.
At 13 billion years old, the galaxy lies near the end of the reionisation epoch, during which most of the hydrogen gas between galaxies transitioned from being mostly neutral to being mostly ionised, and the stars appeared for the first time.
The discovery shows how gravitational lensing can help us understand the faint galaxies that dominate this important period of the early universe, Huang said.

"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 ionised about 13 billion years ago? That's when stars turned on and matter became more complex," said Marc Kassis, staff astronomer at the Keck Observatory.
The galaxy's magnified images were originally seen separately in both Keck Observatory and Hubble Space Telescope data.
Researchers used the DEIMOS (DEep Imaging and Multi-Object Spectrograph) instrument on the 10-metre Keck II telescope to confirm that the three images were of the same object.

The study was published in the Astrophysical Journal Letters.