Most distant galaxy shines light on early universe

JOHNS HOPKINS (US) — Astronomers have spotted what could be the most distant galaxy ever seen.

Light from the young galaxy—captured by NASA’s orbiting Spitzer and Hubble space telescopes—started its sojourn toward Earth when the now-13.7-billion-year-old universe was just 500 million years old.

The far-off galaxy is seen as it existed during an important period, when the universe began to transit out of its so-called “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 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,” says Wei Zheng, a principal research scientist in physics and astronomy at the Johns Hopkins University and lead author of a paper appearing in Nature on Sept. 20.

“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,” adds Zheng.

Five wavebands

Light from the primordial galaxy traveled approximately 13.2 billion light-years before reaching NASA’s telescopes. In other words, the starlight snagged by Spitzer and Hubble left the galaxy when the universe was just 3.6 percent of its present age.

Unlike previous detections of possible galaxies in this age range, 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 program, the Hubble Space Telescope registered it in four wavelength bands. Spitzer located it in a fifth band with its Infrared Array Camera.

Objects at these extreme distances are mostly beyond the detection sensitivity of today’s largest telescopes. To catch sight of such early, distant galaxies, astronomers rely on “gravitational lensing.”

The gravity of foreground objects warps and magnifies the light from background objects as that light passes by en route to Earth. A massive galaxy cluster situated between our galaxy and the early galaxy magnified the latter’s light, brightening the remote object some 15 times and bringing it into view.

Based on the Spitzer and Hubble observations, astronomers think the distant galaxy was spied at a time when it was less than 200 million years old. It also is small and compact, containing only about 1 percent of our Milky Way’s mass.

According to leading cosmological theories, the first galaxies should indeed have started out tiny. They then progressively merged, eventually growing into the sizable galaxies of the more modern universe.

End of the Dark Ages

These first galaxies likely played the dominant role in the epoch of reionization, the event that signaled the demise of the Dark Ages.

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 these earliest galaxies is thought to have caused the neutral hydrogen strewn throughout the universe to ionize, or lose an electron, the state in which the gas has remained since that time.

“In essence, during the epoch of reionization, the lights came on in the universe,” says co-author Leonidas Moustakas, a research scientist at NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology.

Astronomers plan to study the rise of the first stars and galaxies and the epoch of reionization with the successor to both Spitzer and Hubble—NASA’s James Webb Telescope, slated for launch in 2018. The newly described distant galaxy will likely be a prime target.

Holland Ford, one of Zheng’s Johns Hopkins colleagues and a co-author on the paper, says that the first few hundred million years after the birth of the universe is an exciting frontier of scientific knowledge.

With Zheng’s discovery, “we are seeing a galaxy when it was not even a toddler,” Ford says. “But this infant galaxy will in its future grow to be a galaxy like our own, hopefully hosting planetary systems with astronomers who will look back in time and see our galaxy in its infancy.”

The study in Nature is accompanied by a commentary written by astronomer Daniel Stark of the University of Arizona.

Source: Johns Hopkins University