Its record-holding galaxy is 32 billion light-years away, in a Universe that’s only 13.8 billion years old.
On April 24, 2020, humanity celebrates the 30th anniversary of NASA’s Hubble Space Telescope.
This photo shows the Hubble Space telescope being deployed, on April 25, 1990, one day after its launch. It was taken by the IMAX Cargo Bay Camera (ICBC) mounted aboard the space shuttle Discovery. It has been operational for 30 years, and has not been serviced since 2009. With a 2.4-meter diameter mirror, it gathers as much light in 1 minute as a 160-mm (6.3″) telescope would require 3 hours and 45 minutes to gather. (NASA/SMITHSONIAN INSTITUTION/LOCKHEED CORPORATION)
No optical observatory has peered farther into the depths of the distant Universe.
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, as well as information beyond that which we have no known way of gathering. (NASA, ESA, H. TEPLITZ AND M. RAFELSKI (IPAC/CALTECH), A. KOEKEMOER (STSCI), R. WINDHORST (ARIZONA STATE UNIVERSITY), AND Z. LEVAY (STSCI))
Yet even Hubble must reckon with certain fundamental limits.
The Hubble Space Telescope, as imaged during its last and final servicing mission. Although it hasn’t been serviced in over a decade, Hubble continues to be humanity’s flagship ultraviolet, optical, and near-infrared telescope in space, and has taken us beyond the limits of any other space-based or ground-based observatory. (NASA)
Hubble can only observe ultraviolet, visible, and near-infrared light; longer wavelengths are undetectable.
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: around 2,000 nanometers in wavelength. (LARRY MCNISH OF RASC CALGARY CENTER)
Consequently, the expansion of the Universe stretches light’s wavelength, fundamentally limiting Hubble’s vision.
Fewer galaxies are seen nearby and at great distances than at intermediate ones, but that’s due to a combination of galaxy mergers and evolution and also being unable to see the ultra-distant, ultra-faint galaxies themselves. Many different effects are at play when it comes to understanding how the light from the distant Universe gets redshifted, as well as the limits of what we can presently see. (NASA / ESA)
Even with deep-field imaging, Hubble’s observations can only go so faint.
Even the light from smallest, faintest, most distant galaxies ever identified must travel through the Milky Way’s dust. Without knowing how much reddening is due to dust, photometric data concerning the faintest galaxies could be miscalibrated, but spectroscopic investigations offer an unambiguous signature of the distances to these galaxies. (NASA, ESA, R. BOUWENS AND G. ILLINGWORTH (UC, SANTA CRUZ))
With a little serendipity, however, gravitational lensing — where foreground masses bend and magnify background light — provides enhancements.
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, as there is an area located a specific distance away from any given mass distribution, including galaxies and galaxy clusters, where the brightness enhancements will be maximized. (STSCI/NASA/CATS TEAM/R. LIVERMORE (UT AUSTIN))
Furthermore, beyond a certain, early point, the Universe is filled with light-blocking neutral atoms.
Schematic diagram of the Universe’s history, highlighting reionization. Before stars or galaxies formed, the Universe was full of light-blocking, neutral atoms. Most of the Universe doesn’t become reionized until 550 million years afterwards, with some regions achieving full reionization earlier and others later. The first major waves of reionization begin happening at around 250 million years of age, requiring a seredipitous line-of-sight to detect anything earlier than an age of 550 million years. (S. G. DJORGOVSKI ET AL., CALTECH DIGITAL MEDIA CENTER)
In 2016, Hubble overcame all these obstacles
to shatter the cosmic distance record.
A section of the GOODS-N field, which contains the galaxy GN-z11, the most distant galaxy ever observed. At a redshift of 11.1, a distance of 32.1 billion light-years, and an inferred age of the Universe of 407 million light-years at the time this light was emitted, this is the farthest back we’ve ever seen a luminous object in the Universe. (NASA, ESA, G. BACON (STSCI), A. FEILD (STSCI), P. OESCH (YALE UNIVERSITY))
The unprecedented galaxy, GN-z11,
is visible from 13.4 billion years ago: when the Universe was 3% its present age.
Factoring in the expanding Universe, it’s presently 32 billion light-years away.
The galaxy GN-z11 is so far away in the expanding Universe that the shortest-wavelength light we can see from it today, corresponding to light that was emitted in the ultraviolet part of the spectrum, is now at ~1,600 nanometers: more than double the maximum wavelength of the visible light capable of being detected by the human eye. (P.A. OESCH ET AL. (2016), APJ 819, 2, 129)
GN-z11’s light was only perceptible in Hubble’s longest-wavelength infrared bands.
The Great Observatories Origins Deep Studies North field (GOODS-N), cropped to show the Universe’s most distant galaxy, in red. A combination of Hubble and Spitzer data was used to discover this galaxy, whose distance has been confirmed spectroscopically. (NASA, ESA, G. ILLINGWORTH (UNIVERSITY OF CALIFORNIA, SANTA CRUZ), P. OESCH (UNIVERSITY OF CALIFORNIA, SANTA CRUZ; YALE UNIVERSITY), R. BOUWENS AND I. LABBÉ (LEIDEN UNIVERSITY), AND THE SCIENCE TEAM)
It was gravitationally lensed, providing a critical brightness enhancement.
Only because this distant galaxy, GN-z11, is located in a region where the intergalactic medium is mostly reionized, can Hubble reveal it to us at the present time. To see further, we require a better observatory, optimized for these kinds of detection, than Hubble. (NASA, ESA, AND A. FEILD (STSCI))
And it was favorably located along an unlikely, mostly reionized line-of-sight.
With superior capabilities across the board,
NASA’s upcoming James Webb Space Telescope will someday surpass this record.
The James Webb Space Telescope vs. Hubble in size (main) and vs. an array of other telescopes (inset) in terms of wavelength and sensitivity. It should be able to see the truly first galaxies, the earliest, most pristine stars, the smallest directly imaged planets and more. Its power is truly unprecedented, as it’s more than an order of magnitude better than Spitzer across all relevant wavelengths. (NASA / JWST SCIENCE TEAM)
Mostly Mute Monday tells an astronomical story in images, 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.