This seemingly time-defying image by the James Webb Space Telescope (JWST) was possible thanks to the massive gravitational pull of a foreground galactic cluster and a light-bending phenomenon predicted by Albert Einstein over a century ago called “gravitational lensing.”
In his general theory of relativity, Einstein predicted that mass distorts the very fabric of space and time, or “spacetime”. This is analogous to placing a ball on a stretched rubber sheet, where the ball causes a dent in the sheet. The greater the mass of the ball, the greater the degree of twisting it causes. This is also true in the case of spacetime, stars cause a greater “distortion” than planets, and galaxies cause a greater distortion of space than stars.
This warping affects the passage of light as it moves past the mass object from a background object. In extreme cases, because light can take different paths around the lens object from the background lens on its way to us, it can cause the background object to be magnified or even appear at multiple points in the sky. This means that this phenomenon, “gravitational lensing”, has become a powerful tool for astronomers to study very distant objects.
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The lens object in this new JWST image is the galactic cluster RX J2129, located about 3.2 billion light-years away in the constellation Aquarius. RX J2129 lenses a red-colored background supernova-hosting galaxy that replicates it.
The supernova explosion was discovered by astronomers using the Hubble Space Telescope and is a type Ia supernova designated AT 2022riv. These are often referred to as “standard light” by astronomers because of how uniform their light is. This uniformity means that Type Ia supernovae can actually be used as a tool to measure cosmic distances because, at the same distance, they would look exactly the same.
As a gravitational lens, RX J2129 has created three images of this galaxy that are not equal in size, position or even age due to the different paths the light from the background galaxy takes and thus the different times it arrives at JWST. .
The light that follows the longest path shows the background galaxy at its oldest age and at a time when its supernova was still occurring. The next image from the second longest path shows the galaxy just 320 days later, and the last with the shortest light path 1,000 days after the first. In both of these later images, supernova AT 2022riv has already faded from view.
In the upper right corner of the image, several background objects are also shown, which, due to the distortion effect of the gravitational lenses, appear as concentric arcs of light.
The observations were made by JWST using its Near-infrared camera (opens in new tab) (NIRSpec), which was able to measure the brightness of AT 2022riv, a very distant and thus early supernova. The powerful space telescope has also been performing spectroscopy on the light from the event, which should allow this distant supernova to be compared with more recently occurring Type Ia supernovae in the local universe.
This comparison could be used to test the accuracy of using these supernovae when measuring distances, thus verifying the results of one of astronomy’s most useful tools.
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