There’s something strange about this image from the Hubble Space Telescope. If you look closely, you can see two almost mirror image, orange galaxies, connected by a long filament.
Interestingly, those are not two galaxies but one, named SGAS J143845+145407. It appears to be just two, the gravity of a larger object (or objects like a galaxy cluster) distorts the way distant light travels through space.
Imagine placing a heavy weight on a trampoline, where the weight represents the galaxy cluster and the trampoline mat represents space-time. Now roll some marbles from one side of the trampoline to the other. Their normally ‘straight’ paths are not like rays of light through warped space, but appear to diverge along different paths.
Called gravitational lensing, this quirk of gravity can be used to magnify the light of background galaxies that would otherwise be too far away to see in detail, as illustrated in the figure below.
A gravitational lens can thus be an important tool for understanding the distant universe.
Sometimes that light can get really smelly and distorted, as seen in a recent deep field image from the James Webb Space Telescope. Those strange, wobbly, worm-like objects are magnified galaxies. When the lensing effect results in four images of a distant object surrounding the central lensing mass, it is called an Einstein cross.
SGAS J143845+145407 appears at just the right point behind a small galaxy cluster for gravitational lensing to produce two nearly perfect images of the galaxy, with the added bonus of making both appear larger and more detailed.
Light from SGAS J143845+145407 traveled about 6.9 billion years to reach us. This is half the current age of the universe. The cluster’s light traveled about 2.8 billion years.
SGAS J143845+145407 is scientifically interesting because it is a bright infrared galaxy, shining relatively brightly due to high star formation activity. Studying galaxies like these can help scientists understand star formation and how it has changed over the history of the universe; For this type of work, gravity lenses can be invaluable.
Using gravitational lensing, scientists were recently able to reconstruct the distribution of star formation in SGAS J143845+145407 and study the details of the process. They found that the galaxy is very distinctive of its type, information that will help to reference and characterize other galaxies.
The web is expected to reveal more details, but Hubble revolutionized the study of galactic galaxies. His observations were the first to resolve details in lensed galaxies, giving scientists an incredible new window into the early universe.