Since the James Webb Space Telescope began scientific operations in July last year, we have been treated to a barrage of images showing space targets from nebulae to deep fields. This month, Webb researchers shared a new image captured by the telescope’s NIRCam instrument that shows both a beautiful galaxy field and an important astronomical phenomenon called gravitational lensing.
The image shows a giant galaxy cluster called RX J2129, located 3.2 billion light-years away, which acts as a magnifying glass, bending light from more distant galaxies beyond. This causes the stretched shape of some of the galaxies in the top right of the image.
One of the lensed galaxies is particularly notable because it contains something special. At the top right, the same galaxy is imaged three times due to lensing. Within this three-lens galaxy is an exceptionally bright event, a Type Ia supernova. These occur when a small but dense star called a white dwarf is part of a binary system with another star and pulls material away from its companion. This goes on until there is too much mass in the white dwarf and it collapses, then it explodes in a tremendously bright flash of light.
The light from these Type Ia supernovae is important for two reasons: first, it is so bright that it can even be seen from another galaxy, and second, it has (usually) constant luminosity. This means astronomers can look at a very distant Type Ia supernova and calculate exactly how far away it is, making it useful for measuring cosmological distances. These objects are called “standard candles”.
This image captures an extremely distant Type Ia supernova, and it’s useful for telling researchers just how strong the gravitational lensing effect must be. To confirm their findings, the researchers also collected data using another of Webb’s instruments, his NIRSpec spectrogram, to measure the composition of the supernova.