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Astronomers Have Detected The Faintest Early-Universe Galaxy Ever

An international team of astronomers has observed the faintest object at the edge of the visible universe. The object is one of the first galaxies ever; when the light detected was emitted, it was less than 17 million years old.

This impressive feat was possible thanks to the power of the Keck Observatory on top of Mauna Kea in Hawaii, as well as to the serendipitous position of this object in the sky. The galaxy appears to be positioned right behind the large galaxy cluster MACS J2129.4-0741, whose intense gravitational field acted like a lens and magnified the light of this distant object.

The gravitational lens produced three images of the same galaxy. By pairing them with each other, the researchers were able to discover that it was actually all from the same object. The discovery is reported in the Astrophysical Journal Letters.

“If the light from this galaxy was not magnified by factors of 11, five and two, we would not have been able to see it,” Kuang-Han Huang, the lead author of the paper, said in a statement.

Image of the cluster taken by Hubble, with the three spectra of the faint lensed images. They have peaks at the same wavelength, hence showing that they belong to the same source. Credit: Bradac/Hst/W. M. Keck Observatory

Small faint galaxies are thought to be the driver of reionization, an early phase of the universe when hydrogen gas formed and the universe post-Big Bang became ionized (lost its electrons), due to the light of the first stars.  

The galaxy has a mass equal to 17 million Suns, which is about 0.01 percent of the mass of the Milky Way. Its diminutive size and its great distance make it a likely member of the population of faint galaxies that drove the epoch of reionization.

“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,” added Marc Kassis, a staff astronomer at the Keck Observatory, who helped the discovery team. “That’s when stars turned on and matter became more complex.”

Next-generation observatories like the James Webb Space Telescope will be able to discover more of these objects, probing the distant universe and providing answers to its mysteries.  

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