Cosmic Magnifying Lens Unveils Oldest Galaxy
This Hubble Space Telescope image shows distant galaxies brought into view by a cosmic magnifier, the galaxy cluster Abell 2218. Astronomers used another cluster to image an even more distant galaxy. NASA/Space Telescope Science Institute
Scientists have discovered the strongest evidence yet for a 13.2-billion-year old galaxy, a finding that provides a key piece of information about the universe's early childhood.
"This is the most distant (galaxy) identified with high confidence," astronomer Wei Zheng, with Johns Hopkins University, told Discovery News.
"If our current universe is a man of 70 years of age, we have reached an 'infant' of 2.5-years young," Zheng wrote in an email. "It is like an archaeologist finding an oldest piece in history."
From the cosmic microwave background radiation, scientists figure that the universe began about 13.7 billion years ago. It evolved quickly. By the time the universe was 1.4 billion years old, it not only was filled with galaxies, but the hydrogen gas between the galaxies had become highly ionized.
The universe's baby steps to reach this stage are largely missing from the picture, primarily because telescopes to image objects back that far in time are still in the planning stages. But Zheng and colleagues found another way.
Objects with extremely powerful gravity, such as a cluster of galaxies, will bend and sometimes magnify light from a more distant object, relative to Earth's line of sight.
Occasionally, the warped space will bring into focus a more distant object, a phenomenon known as gravitational lensing.
That is what Zheng and colleagues counted on when they used the Hubble Space Telescope to search for magnified galaxies behind some massive nearby clusters.
They found one, magnified by a factor of 15 times, that is believed to date back to just 500 million years after the Big Bang. The magnifier, a massive galaxy cluster known as MACS1149+2223, is one of the most powerful gravitational lenses in the sky, with a mass of 2 million billion suns.
"Even with the deepest images yet obtained by Hubble's infrared camera, it has proved extremely difficult to break through to the first 500 million years of cosmic time," noted University of Arizona astronomer Daniel Stark.
"Researchers have unveiled more than 100 galaxies thought to lie between 650 million and 850 million years after the Big Bang, but only one galaxy had been found that could be dated back to 500 million years," he wrote in this week's Nature.
Since only a very small portion of the sky was covered in Zheng's survey, the team figures they either got incredibly lucky, or the universe is filled with similar distant galaxies. The newly discovered galaxy is believed to be very compact and small — about 0.1 percent the size of the Milky Way galaxy.
"The fact we found one such object in a small volume hints for the abundance of such objects in the early universe," Zheng said.
"We are likely just seeing the tip of the iceberg," added Stark.
A clearer view of the early universe should come into focus once Hubble's successor, the James Webb Space Telescope, or JWST, is launched in about six years.
"We are using Mother Nature's lenses to mimic the JWST performance with the Hubble Space Telescope," Zheng said.
The research appears in this week's Nature.