The light from the distant galaxy in which the supernova exploded was gravitationally lensed by the foreground galaxy cluster RX J2129.6+0005 (abbreviated as RX J2129). Galaxy clusters contain thousands of galaxies of all ages, shapes and sizes. As a rule, their mass is about one million billion times the mass of the Sun.
Albert Einstein predicted in his general theory of relativity that massive objects warp the fabric of space itself. When light passes through one of these objects, such as a massive cluster of galaxies, its path changes slightly. This effect, called gravitational lensing, is only rarely seen, and only the best telescopes in the world can observe the phenomena associated with it.
“Gravity lensing occurs when a massive celestial body causes space-time to curve enough to bend the path of light passing by or through it, almost like a huge lens,” the astronomers say.
In this case, the lens is the galaxy cluster RX J2129, located about 3.2 billion light-years from Earth in the constellation of Aquarius. Gravitational lensing can lead to strange distortions of background objects, which can be seen in the concentric arcs of light in the upper right corner of the Webb image.
Astronomers discovered a supernova called AT 2022riv in the background galaxy using observations from the NASA/ESA Hubble Space Telescope, and they suspected that this object was a very distant Type Ia supernova.
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Type Ia supernovae always produce a relatively constant luminosity—at the same distance, one looks as bright as any other—which makes them especially useful to astronomers.
Since their distance from Earth is proportional to how dim they appear in the night sky, objects of known brightness can be used as “standard candles” to measure astronomical distances.
The near-uniform luminosity of a Type Ia supernova could also allow astronomers to understand how much the RX J2129 galaxy cluster magnifies background objects, and therefore how massive the galaxy cluster is.
“In addition to distorting images of background objects, gravitational lenses can make distant objects appear much brighter,” the astronomers said.
The above image was taken by the Webb Near-Infrared Brightness Measurement Camera AT 2022riv. In the framework of the same program, the spectra of a lensed supernova were obtained using the Webb near-infrared spectrograph.
The data obtained will make it possible to compare this distant supernova with type Ia supernovae in the neighboring Universe.
This is an important way to make sure that one of the methods currently available for measuring long distances is working properly.
