Ultra-distant galaxy spied amidst cosmic 'Dark Ages'

Light from the young galaxy captured by the orbiting observatories was emitted when our 13.7-billion-year-old universe was just 500 million years old. Their work is published September 20 by Nature.

The far-off galaxy existed within an important era when the universe just emerged from the so-called cosmic Dark Ages. During this period, the universe went from a dark, starless expanse to a recognizable cosmos full of galaxies. The discovery of the faint, small galaxy therefore opens up a window into the deepest, remotest epochs of cosmic history.

“This galaxy is the most distant object we have ever observed with high confidence,” said lead author Wei Zheng of Johns Hopkins University. “Future work involving this galaxy—as well as others like it that we hope to find— will allow us to study the universe's earliest objects and how the Dark Ages ended.”

Light from the primordial galaxy traveled approximately 13.2 billion light-years before reaching NASA's telescopes. In other words, the starlight snagged by Hubble and Spitzer left the galaxy when the universe was just 3.6 percent of its present age. Technically speaking, the galaxy has a redshift, or “z,” of 9.6. (Redshift is a term used by astronomers to mark cosmic distances by denoting how much an object's light has shifted into shorter wavelengths due to the expansion of the universe.)

Unlike previous detections of this epoch's galaxy candidates, which were only glimpsed in a single color, or waveband, this newfound galaxy has been seen in five different wavebands. As part of the Cluster Lensing And Supernova survey with Hubble (CLASH) program, the Hubble Space Telescope registered the newly described, far-flung galaxy in four visible and infrared wavelength bands, and Spitzer measured it in a fifth longer-wavelength infrared band, placing the discovery on firmer ground.

Objects at these extreme distances are mostly beyond the detection sensitivity of today's largest telescopes. To catch sight of these early, distant galaxies, astronomers rely on “gravitational lensing.” In this phenomenon, predicted by Albert Einstein a century ago, the gravity of foreground objects warps and magnifies the light from background objects. A massive galaxy cluster situated between our galaxy and the newfound, early galaxy magnified the latter's light, brightening the remote object some 15 times and bringing it into view.

Based on the Hubble and Spitzer observations, astronomers think the distant galaxy is less than 200 million years old. It is also small and compact, containing only about one percent of the Milky Way's mass. According to leading cosmological theories, the first galaxies should indeed have started out tiny. They then progressively merged, eventually accumulating into the sizable galaxies of the more modern universe.

“These first galaxies likely played the dominant role in the epoch of reionization, the event that signaled the end of the universe's Dark Ages,” Kelson said. “In essence, the light was finally able to penetrate the fog of the universe.”

About 400,000 years after the Big Bang, neutral hydrogen gas formed from cooling particles. The first luminous stars and their host galaxies, however, did not emerge until a few hundred million years later. The energy released by the earliest galaxies is thought to have caused the neutral hydrogen strewn throughout the universe to ionize, or lose an electron, a state that the gas has remained in since that time.

Astronomers plan to study the rise of the first stars and galaxies and the epoch of reionization with the successor to both the Hubble and Spitzer telescopes, NASA's James Webb Telescope, slated for launch in 2018. The newly described, distant galaxy will likely be a prime target given the fortuitousness of it being so strongly gravitationally lensed.

The CLASH program is based on observations made with the NASA/ESA Hubble Space Telescope. The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy Inc. under NASA contract. This work is also based in part on archival data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

The Carnegie Institution for Science (carnegiescience.edu) is a private, nonprofit organization headquartered in Washington, D.C., with six research departments throughout the U.S. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.