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CosmosUp | March 22, 2019

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Astrophysicists have Detected The Faintest Galaxy Known So Far

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Using the W. M. Keck Observatory located on the summit of Mauna Kea, Hawaii, astrophysicists at University of California have detected the faintest galaxy ever, born just after the Big Bang.

The team of scientists relied on gravitational lensing, in addition to Keck Observatory — the world’s largest optical and infrared telescopes, to see such incredible faint object; Its so faint that astronomers need a supermassive cluster of galaxy to magnify and create different images of the object.

The galaxy in question is also very old, astronomers see the galaxy as it was 13 billion years ago when the universe was only 3 percent of its current age.

Keck Observatory’s telescopes are simply the best in the world for this work,

said Marusa Bradac ~ lead author of the study published in The Astrophysical Journal Letters.

Their power, paired with the gravitational force of a massive cluster of galaxies, allows us to truly see where no human has seen before.

Because you see three of them and the characteristics are exactly the same, that means it was lensed,

said Marc Kassis ~ assists the discovery team at night.

The other thing that is particularly interesting is that it is small. The only way they would have seen it is through lensing. This allowed them to identify it as an ordinary galaxy near the edge of the visible Universe.

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,

said Kuang-Han Huang ~ also lead author of the paper.

It lies near the end of the reionization epoch, during which most of the hydrogen gas between galaxies transitioned from being mostly neutral to being mostly ionized (and lit up the stars for the first time). That shows how gravitational lensing is important for understanding the faint galaxy population that dominates the reionization photon production.

 The galaxy’s magnified images were originally seen separately in both Keck Observatory and Hubble Space Telescope data. Scientists collected and combined all spectra from all three images and thus confirming they were the same and that this is a triply-lensed system.

We now have good constraints on when the reionization process ends – at redshift around 6 or 12.5 billion years ago – but we don’t yet know a lot of details about how it happened,

Huang said.

The galaxy detected in our work is likely a member of the faint galaxy population that drives the reionization process.

This galaxy is exciting because the team infers a very low stellar mass, or only one percent of one percent of the Milky Way galaxy,

Kassis 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 ionized about 13 billion years ago. That’s when stars turned on and matter became more complex.

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