Faintest 'normal' early galaxy ever discovered

Gravitational lensing has allowed astronomers to spy on a 'typical' galaxy as it was in the days of the early Universe. This find will allow them to study the most numerous kind of fledgling galaxy present during this highly important era.

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As the distant galaxy was gravitionally lensed by a closer galaxy cluster (centre inset), astronomers were able to not only image the faint galaxy using Hubble (top right inset), but take its spectra with the Keck telescope (bottom right inset). 
Credit: NASA/Keck/Austin Hoag/Marusa Bradac

Astronomers have managed to image the faintest galaxy in the Universe ever spotted, the light of which dates from 13.1 billion years ago. But this galaxy has one unique property over all those observed before – it’s completely normal.

“Other most distant objects are extremely bright and probably rare compared to other galaxies,” says Austin Hoag, the University of California, Davis graduate student who led the discovery. “We think this is much more representative of galaxies of the time.”

The galaxy, MACS1423-z7p64, is at a redshift of 7.6, a distance so immense that astronomers had to rely on gravitational lensing to find it. Lensing happens when light from a distant object passes by a massive foreground object, it can cause the light to bend and be magnified, as if passed through a lens.

The galaxy dates from a critical period of the Universe’s history – the epoch of reionization, when space became transparent.

After the Big Bang, the Universe was filled with cold atomic hydrogen, which blocked most light from travelling very far. As the first stars and galaxies began to condense out of this haze, the light they emitted began to burn away the hydrogen, like the Sun clearing a morning fog.

However, this ‘fog of reionization’ hides much of what was occurring during this important era when the stars first began to shine. The newly found galaxy will help astronomers untangle the mysteries around this time, such as whether it was solely young galaxies that were responsible for the reionisation, or if black holes and gamma ray bursts contributed as well.


Read more about the early Universe on BBC Sky at Night Magazine:


To find the galaxy, astronomers hunted around galaxy clusters of the right size and distance to lens a galaxy from the epoch of reionisation. It was chance that MACS1423-z7p64 happened to fall in precisely the right position that its brightness was magnified by a factor of ten, allowing observers to capture it with the Hubble Space Telescope. The galaxy was further imaged by the Keck Observatory Telescope in Hawaii, and study will continue with the James Webb Space Telescope, which is due to launch in 2018.

“We will truly witness the birth of the first galaxies which will allow us to answer the longstanding question of where did we come from,” says Marusa Bradac, a physics professor from the University of California, Davis.

Carouselle image credit: NASA/ESA


 

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