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Starts With A Bang

This Is Why Hubble Can’t See The Very First Galaxies

These three reasons are why there’s no getting around the fact that astronomy needs the James Webb Space Telescope.

Even the most powerful telescope in history, the Hubble Space Telescope, can’t do it all.

This NASA/ESA Hubble Space Telescope image shows a massive galaxy cluster, PLCK_G308.3–20.2, glowing brightly in the darkness. It was discovered by the ESA Planck satellite through the Sunyaev-Zel’dovich effect — the distortion of the cosmic microwave background radiation in the direction of the galaxy cluster by high-energy electrons in the intracluster gas. The large galaxy at the center is the brightest galaxy in the cluster, and above it a thin, curved gravitational lens arc is visible. This is what huge swaths of the distant Universe looks like. (ESA/HUBBLE & NASA, RELICS; ACKNOWLEDGEMENT: D. COE ET AL.)

The most distant discovered galaxies are all Hubble’s, but it’s unlikely to go farther.

Various long-exposure campaigns, like the Hubble eXtreme Deep Field (XDF) shown here, have revealed thousands of galaxies in a volume of the Universe that represents a fraction of a millionth of the sky. But even with all the power of Hubble, and all the magnification of gravitational lensing, there are still galaxies out there beyond what we are capable of seeing. (NASA, ESA, H. TEPLITZ AND M. RAFELSKI (IPAC/CALTECH), A. KOEKEMOER (STSCI), R. WINDHORST (ARIZONA STATE UNIVERSITY), AND Z. LEVAY (STSCI))

By observing dark, empty patches of sky, it reveals ancient galaxies without nearby interference.

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. But scientists using Hubble are up to the challenge. (NASA, ESA, AND J. LOTZ (STSCI))

When distant galaxy clusters are present, these massive gravitational clumps behave as natural magnifying lenses.

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. (NASA, ESA, M. POSTMAN AND D. COE (STSCI), AND THE CLASH TEAM)

The most distant observed galaxies have their light bent, distorted, and amplified along the journey.

The smallest, faintest, most distant galaxies identified in the deepest Hubble image ever taken. The 2017 Livermore et al. study has them beat, by perhaps two orders of magnitude, thanks to stronger gravitational lenses. (CREDIT: NASA, ESA, R. BOUWENS AND G. ILLINGWORTH (UC, SANTA CRUZ))

Hubble discovered the current cosmic record-holder, GN-z11, via lensing.

The most distant galaxy ever found: GN-z11, in the GOODS-N field as imaged deeply by Hubble. The same observations that Hubble made to obtain this image will give WFIRST sixty times the number of ultra-distant galaxies. (NASA, ESA, AND P. OESCH (YALE UNIVERSITY))

Its light arrives from 407 million years after the Big Bang: 3% of the Universe’s current age.

The galaxy cluster MACS 0416 from the Hubble Frontier Fields, with the mass shown in cyan and the magnification from lensing shown in magenta. That magenta-colored area is where the lensing magnification will be maximized. Mapping out the cluster mass allows us to identify which locations should be probed for the greatest magnifications and ultra-distant candidates of all. But to get the first galaxies, we’ll need a better-optimized observatory than Hubble.(STSCI/NASA/CATS TEAM/R. LIVERMORE (UT AUSTIN))

Three reasons combine to limit Hubble’s potential beyond this.

The Hubble Space Telescope, as imaged during its last and final servicing mission. Despite its reflective exterior, its proximity to the Earth, lack of active-or-passive cooling, and exposure to the Sun ensures that it will remain too warm to view longer-wavelength light than about 1700 nanometers. (NASA)

1.) Despite its reflective outsides, Hubble resides in low-Earth orbit, with no active cooling.

The powerful imaging capabilities of Hubble’s Wide Field Camera 3 allows us to see farther than every before into the distant Universe. But even with this instrument and its UV, visible, and infrared eyes, there are limits beyond which imaging is impossible with this technology. (NASA/AMANDA DILLER)

Its instruments are therefore warm; it cannot observe mid-infrared light.

Light may be emitted at a particular wavelength, but the expansion of the Universe will stretch it as it travels. Light emitted in the ultraviolet will be shifted all the way into the infrared when considering a galaxy whose light arrives from 13.4 billion years ago; the Lyman-alpha transition at 121.5 nanometers becomes infrared radiation at the instrumental limits of Hubble. (LARRY MCNISH OF RASC CALGARY CENTER)

2.) More distant galaxies have their light redshifted by cosmic expansion.

Past a certain distance, or a redshift (z) of 6, the Universe still has neutral gas in it, which blocks-and-absorbs light. These galactic spectra show the effect as a drop-to-zero in flux to the left of the big (Lyman-series) bump for all the galaxies past a certain redshift, but not for any of the ones at lower redshift. This physical effect is known as the Gunn-Peterson trough, and block the brightest light from the most distant stars and galaxies. (X. FAN ET AL, ASTRON.J.132:117–136, (2006))

Hubble’s wavelength limit, 1700 nanometers, corresponds to 326 million years after the Big Bang.

Schematic diagram of the Universe’s history, highlighting reionization. Before stars or galaxies formed, the Universe was full of light-blocking, neutral atoms. While most of the Universe doesn’t become reionized until 550 million years afterwards, with the first major waves happening at around 250 million years, a few fortunate stars may form just 50-to-100 million years after the Big Bang, and with the right tools, we may reveal the earliest galaxies. (S. G. DJORGOVSKI ET AL., CALTECH DIGITAL MEDIA CENTER)

3.) But the Universe is filled with light-blocking gas until it’s 550 million years old.

The farthest galaxy ever spectroscopically confirmed. To push the frontiers even farther, we’ll need to go even deeper into the Universe, which means seeing through the light-blocking gas-and-dust that populates the early Universe. (NASA, ESA, AND A. FEILD (STSCI))

Finding GN-z11 was serendipitous; it resides along a very rare, clear line-of-sight.

An artist’s conception (2015) of what the James Webb Space Telescope will look like when complete and successfully deployed. This will be the key observatory in finding the Universe’s most distant galaxies: the ones that Hubble cannot reveal. (NORTHROP GRUMMAN)

Only James Webb, with its distant orbit — and cooled, optimized instruments — will take us farther.

As we’re exploring more and more of the Universe, we’re able to look farther away in space, which equates to farther back in time. The James Webb Space Telescope will take us to depths, directly, that our present-day observing facilities cannot match. (NASA / JWST AND HST TEAMS)

Mostly Mute Monday tells the astronomical story of an object, image, or phenomenon in visuals and no more than 200 words. Talk less; smile more.

Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.


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