A well-placed cluster puts a distant galaxy under a high-powered lens

Gravitational lensing shows astronomers a galaxy that’s strangely dormant when most others are busy forming stars.
By | Published: February 5, 2018
The galaxy eMACSJ1341-QG-1, outlined in yellow, appears long and snakelike due to distortion from gravitational lensing. It is magnified by a factor of 30, as its light is bent around an intervening galaxy cluster. The red boxed inset shows the distant, quiescent galaxy as it would appear without distortion.
Harald Ebelling, University of Hawaii, Institute for Astronomy
The farther away an object lies, the smaller it appears. Astronomers build large telescopes to identify and study faraway objects, but sometimes the universe steps in and provides a “natural” telescope of its own through a process called gravitational lensing. Intervening matter, from single stars to entire galaxy clusters, can act as a gravitational lens, bending the light from objects behind them to produce a bright, magnified image of something that might otherwise be difficult or impossible to see. Such is the case with eMACSJ1341-QG-1 — a distant galaxy that is magnified 30 times by an intervening galaxy cluster, allowing astronomers an unparalleled look at its structure.

eMACSJ1341-QG-1 exists at a time when the universe was just about four billion years old. It is a quiescent galaxy that is not forming new stars from its gas and dust. While it is not the farthest such galaxy detected, eMACSJ1341-QG-1 is the most highly magnified quiescent galaxy found to date. The discovery, published December 27 in the Astrophysical Journal Letters, is the result of work by team of astronomers led by Harald Ebeling of the Institute for Astronomy at the University of Hawaii. “We specialize in finding extremely massive clusters that act as natural telescopes and have already discovered many exciting cases of gravitational lensing,” he said in a press release. “This discovery stands out though, as the huge magnification provided by [the] eMACSJ1341 [galaxy cluster] allows us to study in detail a very rare type of galaxy.”

eMACSJ1341-QG-1 is rare because it is so quiet at a time when the universe was much younger. During this time, galaxies should be actively forming stars, not sitting quietly, a characteristic more reminiscent of older galaxies today. According to Mikkel Stockmann, a team member from the University of Copenhagen, “As we look at more distant galaxies, we are also looking back in time, so we are seeing objects that are younger and should not yet have used up their gas supply. Understanding why this galaxy has already stopped forming stars may give us critical clues about the processes that govern how galaxies evolve.”

Gravitational lensing occurs when light from a distant object is bent around intervening matter, such as a galaxy cluster. The result is a magnified, distorted image of the background object.
Gravitational lensing, a phenomenon predicted by Einstein, has allowed astronomers to study everything from exoplanets to early galaxies. In addition to creating magnified images of objects unreachable with traditional telescopes, also provides information about the intervening lens object, including its mass. This has allowed astronomers to better study the concentration and distribution of mass in galaxy clusters — including the dark matter they contain. eMACSJ1341.9-2441 is just one of many massive galaxy clusters astronomers are using to learn more about the nearby and distant universe.