There’s something very strange about this image from the Hubble Space Telescope. If you look closely, you can see two near-mirror-image, orange-hued galaxies that appear to be connected by a long filament.
Interestingly, it is not two galaxies, but one, named SGAS J143845+145407. It appears to be just two, due to the way the gravity of a massive object (or objects like a cluster of galaxies) distorts the space through which distant light travels.
Imagine putting 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 seem to curve along different paths, not unlike rays of light through distorted space.
Called gravitational lensing, this aberration of gravity can be used to amplify the light of background galaxies that would be too far away to be seen in great detail, as shown in the figure below.
Illustration of gravitational lensing. (NASA, ESA and El Calcada)
Therefore such gravitational lenses could be an important tool for understanding the distant universe.
Sometimes that light can actually be blurry and distorted, as seen in a recent deep-field image from the James Webb Space Telescope. Those odd, wobbly, worm-like objects are lensed galaxies. When the lensing effect results in four images of a distant object around a central lensing mass, it is called an Einstein cross.
SGAS J143845+145407 appears at the right point just behind a smaller galaxy cluster to produce two nearly complete images of the Milky Way for gravitational lensing, with the added bonus of making these two appear larger and in more detail.
Light from SGAS J143845+145407 has traveled about 6.9 billion years to reach us. This is about half the current age of the universe. The cluster’s light traveled for about 2.8 billion years.
Reflected images of SGAS J143845+145407 around the gravitational lens. (ESA/Hubble and NASA, J. Rigby)
SGAS J143845+145407 is scientifically interesting because it is a luminous infrared galaxy, which shines relatively brightly due to high star formation activity. Studying galaxies in this way can help scientists understand how it has changed over the history of the universe; Gravitational lenses can be invaluable for this type of work.
Using a gravitational lens, 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 would help to refer to and characterize other galaxies.
Webb is expected to reveal even more details, but Hubble revolutionized the study of lensed galaxies. Its observations gave scientists an incredible new window into the early universe, the first to resolve details inside lensed galaxies.
The image has been published on the Hubble website.
