Astronomers using NASA’s Spitzer and Hubble Space Telescopes have discovered what could be the most distant galaxy ever seen.
Light from the young galaxy MACS 1149-JD was emitted when the Universe was just 500 million years old. In other words, the starlight snagged by the telescopes left the galaxy when the Universe was just 3.6 percent of its present age.
“This galaxy is the most distant object we have ever observed with high confidence,” said Dr Wei Zheng of Johns Hopkins University, lead author of a paper published in Nature (arXiv.org version).
“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.”
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 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.
The massive galaxy cluster MACS J1149+2223 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,” said co-author Dr Daniel Kelson of the Observatories of the Carnegie Institution for Science in Pasadena. “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.
_______
Bibliographic information: Wei Zheng et al. 2012. A magnified young galaxy from about 500 million years after the Big Bang. Nature, 489, 406–408; doi: 10.1038/nature11446
