Astronomers find most distant galaxy to date

By Mo-Yu Zhou | October 4, 2012

With the help of NASA’s Hubble and Spitzer Space Telescopes, a team of astronomers led by Hopkins’ Wei Zheng has discovered the most distant – and, hence, the youngest – galaxy ever observed with high confidence.

The telescopes captured light from that galaxy when the universe, now 13.7 billion years old, was just 500 million years of age. The light traveled about 13.2 billion light years before reaching the telescopes.

According to Zheng, a research scientist in the Department of Physics and Astronomy and the lead author of a new paper in Nature regarding this research, these young galaxies’ properties are “critical to our understanding of the early universe.”

The term “redshift” is used to describe cosmic distances, and refers to how much an object’s light has shifted into longer wavelengths due to the universe’s expansion. The galaxy has a redshift of 9.6. Until a few years ago, there was an observational void between redshifts of approximately six to 12 that is just now beginning to be filled with this new discovery.

Objects at a redshift of around 10 are “extremely difficult to find,” Zheng said. Only one or two galaxies at that redshift are known, compared to about 1,000 galaxies at redshift six. “Such objects are very faint, and even the Hubble Space Telescope would take months to find one,” he explains.

The researchers were able to make this significant accomplishment by taking advantage of a gravitational lens. As predicted by Albert Einstein a century ago, the gravity of foreground objects can warp and magnify the light from background objects.

Fortunately for Zheng and his team, there is a massive galaxy cluster that resides between the distant galaxy and our own, creating such a lens and aiding significantly with the new discovery. “With the help of gravitational lensing, we increased the search efficiency more than tenfold,” Zheng said.

Previous detections of galaxies in this age range were only spotted in a single color or waveband. For the first time, a galaxy of this age has been seen in five different wavebands, four from Hubble and a fifth one from Spitzer via its Infrared Array Camera (IRAC), helping solidify the discovery. This was part of the Cluster Lensing and Supernova survey with Hubble (CLASH) program.

Based on these observations, the researchers were able to deduce that the distant galaxy was spotted when it was less than 200 million years old. It contained about one percent of the Milky Way’s mass, meaning that it was small and compact, as would be expected of a galaxy of the time. In fact, current cosmological theories suggest that the first galaxies were tiny; over time, they merged and eventually became the large galaxies of the more modern universe.

This galaxy existed during an important period in cosmic development: the transition from the “Dark Ages.” This era was one of reionization, during which such galaxies played a dominant role. Neutral hydrogen gas had formed around the universe from cooling particles about 400,000 years after the Big Bang, whereas galaxies that contained luminous stars did not form until millions of years later.

It is believed that these early galaxies caused the neutral hydrogen to lose an electron (i.e. ionize), which is a state that the gas has remained in to this day. Thus, the universe, previously a starless expanse of darkness, was on its way to becoming the universe we know today, full of galaxies.

Zheng is also excited about the possibilities that will come with the launch of NASA’s James Webb Space Telescope in 2018. Fifty times as powerful as the Hubble Space Telescope, it will “extend our horizon significantly,” Zheng said, allowing for further discoveries along this vein. Future deep field observations with the James Webb Telescope are likely to continue to take advantage of gravitational lensing, with even more incredible results. According to Zheng, scientists may even find objects at redshifts of around 15 to 20 – “truly an infant universe.”

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