Astronomers using NASA’s Hubble Space Telescope may have spotted the farthest cosmic magnifying glass yet. The powerful gravity from this massive elliptical galaxy magnifies the light coming from a distant spiral galaxy -- breaking the previous “lensing” record by 200 million years.
Gravitational lensing is a phenomenon where a foreground object magnifies, brightens, and distorts images of more distant objects behind it that are typically too faint to see with telescopes. The enormous gravitational field of this monstrous elliptical deflects the light passing through it, the way any optical lens bends light to form an image.
You can see the giant elliptical as it appeared 9.6 billion years ago in the left enlarged image above. It gets its red color from older stars’ light, and it’s one of the brightest members in a distant cluster of galaxies called IRC 0218.
Also in that left inset, the lighter-colored blobs at the upper right and lower left are the distorted, magnified shapes of the more distant spiral galaxy -- located 10.7 billion light-years from Earth. After subtracting the elliptical giant, you get the spiral galaxy in the enlarged image above on the right. It appears blue because of the glow of young stars. (The white area is likely an area of star formation.)
"When you look more than 9 billion years ago in the early universe, you don't expect to find this type of galaxy-galaxy lensing at all," says Kim-Vy Tran of Texas A&M University in a news release. "It's very difficult to see an alignment between two galaxies in the early universe.” Imagine looking through a magnifying glass. Even if you hold it at arm’s length, you’ll still see an enlarged object. “But if you move the magnifying glass across the room,” Tran explains, “your chances of seeing the magnifying glass nearly perfectly aligned with another object beyond it diminishes."
Tran and colleagues combined spectroscopic data from the W.M. Keck Observatory in Hawaii and Hubble in order to determine that the lighter-colored blobby features -- the blue, eyebrow-shaped object next to a smeared blue dot around the big elliptical -- were two images of the same spiral galaxy.
From this chance alignment, the team measured the giant galaxy's total mass -- including its amount of dark matter -- by gauging the intensity of its lensing effects on the background galaxy's light. It weighs 180 billion times more than our sun.
Hundreds of lens galaxies are known, but almost all of them are relatively nearby. With such a distant lens “we can learn about the dark-matter content of galaxies in the distant past... [and] how that dark-matter content has evolved over time,” study author Kenneth Wong of Academia Sinica Institute of Astronomy & Astrophysics in Taipei explains. As hefty as this lensing galaxy is, it’s underweight in terms of dark-matter content. It will probably continue to grow over the next 9 billion years as it cannibalizes neighboring galaxies.
The work was published in the Astrophysical Journal Letters earlier this month.