Something about this Hubble Space Telescope image is very strange. If you look closely you can see two almost mirror-inverted images, orange galaxies seemingly connected by a long filament.
Fascinatingly, these are not two galaxies at all, but one called SGAS J143845+145407. There appears to be only two, thanks to the way the gravity of a massive object (or objects, like a galaxy cluster) distorts the space through which distant light travels.
Imagine placing a heavy weight on a trampoline, with the weight representing the galaxy cluster and the trampoline mat representing spacetime. Now roll some marbles from one side of the trampoline to the other. Their normally “straight” paths appear to curve along different paths, much like rays of light through a distorted space.
This property of gravity, called gravitational lensing, can be used to magnify light from background galaxies that would otherwise be too distant to see in detail, as shown in the diagram below.
Illustration of gravitational lensing. (NASA, ESA & L. Calçada)
Gravitational lenses like these can therefore be an important tool in understanding the distant Universe.
Sometimes that light can get really smeared and distorted, as seen recently James Webb Space Telescope deep field image. These strange, wobbly, worm-like objects are lensed galaxies. If lens flare results in four images of a distant object centered around the central lens mass, this is called an Einstein Cross.
SGAS J143845+145407 appears in just the right place behind a small cluster of galaxies for gravitational lensing to produce two near-perfect images of the galaxy, with the added benefit of both appearing larger and more detailed.
The light from SGAS J143845+145407 traveled approximately 6.9 billion years to reach us. That’s about half the current age of the universe. The cluster’s light has traveled about 2.8 billion years.
Reflected images of SGAS J143845+145407 around a gravitational lens. (ESA/Hubble & NASA, J Rigby)
SGAS J143845+145407 is of scientific interest because it is a glowing infrared galaxy that is relatively bright due to high star forming activity. Studying galaxies like this one can help scientists understand star formation and how it has changed throughout the history of the universe; For this type of work, gravitational lenses can be invaluable.
With the help of gravitational lenses, scientists recently succeeded reconstruct the distribution of star formation in SGAS J143845+145407, and study the details of the process. They found the galaxy to be fairly typical of its type, and this information helps contextualize and characterize other galaxies.
Webb is expected to reveal even more detail, but Hubble has revolutionized the study of lensed galaxies. His observations were the first to resolve details within lens galaxies, giving scientists an incredible new window into the early Universe.
The picture was published on the Hubble website.
