The most distant object ever seen 鈥� a faint galaxy 13 billion light-years away 鈥� has been captured by two of the most powerful telescopes in operation.
The galaxy is seen as it was just 750 million years after the Big Bang, as the Universe was emerging from the cosmic Dark Ages. This was the murky period before the Universe鈥檚 neutral hydrogen atoms were broken apart into the ions that made space transparent.
鈥淵ou鈥檙e seeing the Universe as it was in its infancy,鈥� says Andrew Bunker, an astronomer at Cambridge University, UK, who studies distant galaxies. 鈥淚t鈥檚 a significant discovery because it鈥檚 pushing into the epoch where the Universe is mostly neutral.鈥�
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This area of research is part of an effort to survey the early Universe to see if the first stars and galaxies can account for the ionisation. 鈥淚t鈥檚 an exciting field because we don鈥檛 know the answer,鈥� Bunker told New 杏吧原创.
Chance alignment
An international team of astronomers, led by Jean-Paul Kneib of the Observatoire Midi-Pyr茅n茅es, pushed the Hubble Space Telescope and the world鈥檚 largest optical telescopes, the twin 10-metre Kecks, to their limits to find the galaxy. Even so, the distant galaxy was only visible because of a chance geometric alignment.
A massive galaxy cluster called Abell 2218 lies between the distant galaxy and Earth, and its gravity bent and magnified the galaxy鈥檚 light, making it 25 times brighter.
Astronomers can determine vast distances by how much an object鈥檚 light has been stretched by the expansion of the Universe, a measure called redshift. The previous record holder for the most distant object is a galaxy at redshift 6.5, and last week researchers with the ground-based Sloan Digital Sky Survey announced that they had found 13 quasars with about the same redshift.
The Hubble data suggest the newly observed galaxy lies between redshift 6.6 and 7.1, while long exposures with the Keck telescopes narrow the value to about 7.0.
The galaxy appears to form stars at the rate of nearly three Suns per year and is just 2000 light-years鈥� wide, about 50 times smaller than our Milky Way. Kneib his colleagues will report their observation in an upcoming issue of the Astrophysical Journal.
Further and further
In recent years, astronomers have probed further and further back in space and time. They have discovered that the first stars and galaxies arose from dense gas clouds much more quickly than predicted.
Until recently, quasars 鈥� relatively rare objects thought to be powered by supermassive black holes 鈥� were the only objects visible at the farthest reaches of the Universe because of their extreme brightness.
But with high-resolution telescopes such as Hubble, and boosts from gravitational lenses such as Abell 2218, astronomers have begun to see normal galaxies at such distances.
鈥淕alaxies and quasars are in constant competition [for the record] at the moment,鈥� says Bunker. But he also adds a note of caution, saying that high-redshift measurements must be taken with 鈥渁 pinch of salt鈥� because they are so difficult to make.
