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Starts With A Bang

Faintest galaxies ever seen explain the ‘Missing Link’ in the Universe

How gravitational magnification allows us to see what we’ve never seen before.

“The problem is, you’re trying to find these really faint things, but you’re looking behind these really bright things. The brightest galaxies in the universe are in clusters, and those cluster galaxies are blocking the background galaxies we’re trying to observe.” –Rachael Livermore

To see farther than ever, we point our most powerful space telescopes at a single region and collect light for days.

One of the most massive, distant galaxy clusters of all, MACS J0717.5+3745, was revealed by the Hubble Frontier Fields program. Image credit: NASA / STScI / Hubble Frontier Fields.

The Hubble Frontier Fields program focused on massive galaxy clusters, using their gravity to enhance our sight even further.

Ultra-distant, colliding galaxy clusters have been revealed by the Hubble Frontier Fields program, looking fainter, wider-field and deeper than any other survey before it. Image credit: NASA, ESA, D. Harvey (École Polytechnique Fédérale de Lausanne, Switzerland), R. Massey (Durham University, UK), the Hubble SM4 ERO Team, ST-ECF, ESO, D. Coe (STScI), J. Merten (Heidelberg/Bologna), HST Frontier Fields, Harald Ebeling(University of Hawaii at Manoa), Jean-Paul Kneib (LAM)and Johan Richard (Caltech, USA).

By warping space, the light from background objects gets magnified, revealing extraordinarily faint galaxies.

Gravitational lenses, magnifying and distorting a background source, allow us to see fainter, more distant objects than ever before. Image credit: ALMA (ESO/NRAO/NAOJ), L. Calçada (ESO), Y. Hezaveh et al.

The only problem? The cluster itself is closer and overwhelmingly luminous, making it impossible to tease out the distant signals.

The overwhelmingly large brightness of the galaxies within a foreground cluster, like Abell S1063, shown here, make it a challenge to use gravitational lensing to identify ultra-faint, ultra-distant background galaxies. Image credit: NASA, ESA, and J. Lotz (STScI).

Until now. Thanks to a superior new technique devised by Rachael Livermore, light from the foreground cluster galaxies can be modeled and subtracted, revealing faint, distant galaxies never seen before.

The ultra-distant, lensed galaxy candidate, MACS0647-JD, appears magnified and in three disparate locations thanks to the incredible gravity of the gravitational lens of the foreground cluster, MACS J0647. Image credit: NASA, ESA, M. Postman and D. Coe (STScI), and the CLASH Team.

With Steven Finkelstein and Jennifer Lotz, Livermore has applied this technique to two Frontier Fields clusters already: Abell 2744 and MACS 0416.

The galaxy cluster MACS 0416 from the Hubble Frontier Fields, with the mass shown in cyan and the magnification from lensing shown in magenta. Image credit: STScI/NASA/CATS Team/R. Livermore (UT Austin).

The galaxies that came out were up to 100 times fainter than the dimmest galaxies in the Hubble eXtreme Deep Field, setting a new record.

The smallest, faintest, most distant galaxies identified in the deepest Hubble image ever taken. This new study has them beat, thanks to stronger gravitational lenses. Image credit: NASA, ESA, R. Bouwens and G. Illingworth (UC, Santa Cruz).

From when the Universe was less than 10% of its current age, the light from these faint, young galaxies made the Universe transparent.

The reionization and star-formation history of our Universe, where reionization was driven by these faint, early but theoretically numerous galaxies. At last, thanks to Livermore’s work, we’re discovering them. Image credit: NASA / S.G. Djorgovski & Digital Media Center / Caltech.

Four more Frontier Fields clusters await, while James Webb, launching next year, will extend this technique even further.

An artist’s conception (2015) of what the James Webb Space Telescope will look like when complete and successfully deployed. It will reveal fainter galaxies, using this technique, than Hubble ever could. Image credit: Northrop Grumman.

Mostly Mute Monday tells a story about our Universe in pictures, visuals and no more than 200 words.

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