Webb spotted a second lensed supernova in a distant galaxy

November 2023 witnessed a groundbreaking moment for space exploration as NASA’s James Webb Space Telescope captured a mesmerizing image of MACS J0138.0-2155, an enormous cluster of galaxies. Utilizing the phenomenon of gravitational lensing, predicted by the brilliant mind of Albert Einstein, the telescope revealed the distortion caused by the strong gravitational pull of the galaxy cluster on a distant galaxy named MRG-M0138. This cosmic dance of gravity resulted in the creation of five separate images of MRG-M0138, each magnified and warped.

In an intriguing turn of events, astronomers examining images from the James Webb Space Telescope in 2023 made an unexpected discovery. Alongside the supernova previously observed by NASA’s Hubble Space Telescope in 2016 within the galaxy MRG-M0138, another supernova had occurred in the same galaxy seven years later. This remarkable finding marks the first instance of two gravitationally lensed supernovae being detected within the same galaxy.

Justin Pierel, a NASA Einstein Fellow at the Space Telescope Science Institute, shed light on the phenomenon, stating, “When a supernova explodes behind a gravitational lens, its light reaches Earth through various paths. We can liken these paths to multiple trains departing from a station simultaneously, traveling at the same speed, and heading towards the same destination. However, due to differences in trip length and terrain, these trains do not reach their destination simultaneously.”

Gravitationally lensed supernova images, much like these metaphorical trains, appear to astronomers over varying periods, spanning from days to weeks or even years. By measuring the time differences in the appearance of these supernova images, scientists can gain insights into the history of the universe’s expansion rate, known as the Hubble constant. This measurement poses a significant challenge in the field of cosmology today. However, the scarcity of multiply-imaged supernovae makes this task exceptionally difficult, with fewer than a dozen such occurrences being detected thus far.

The 2016 supernova, named Requiem, within MRG-M0138 stood out due to its unique characteristics. Firstly, it was located an astounding 10 billion light-years away. Secondly, this supernova belonged to the type Ia category, widely recognized as a ‘standard candle’ for measuring cosmic distances.

Supernova RequiemSupernova Requiem
Left: In 2016, NASA’s Hubble Space Telescope captured a multiply-imaged supernova, affectionately named Supernova Requiem, in a distant galaxy lensed by the intervening galaxy cluster MACS J0138. Three of the supernova’s images are visible, with a fourth expected to arrive in 2035. The image depicts light at 1.05 microns in blue and 1.60 microns in orange. Right: In November 2023, NASA’s James Webb Space Telescope, employing its NIRCam (Near-Infrared Camera) instrument, identified a second multiply-imaged supernova within the same galaxy. This astounding discovery marks the first known occurrence of multiple multiply-imaged supernovae in a single system. Image credits: NASA, ESA, STScI, Steve A. Rodney (University of South Carolina), Gabriel Brammer (Cosmic Dawn Center/Niels Bohr Institute/University of Copenhagen), Justin Pierel (STScI), and Andrew Newman (Carnegie Institution for Science).

What makes the 2016 supernova in MRG-M0138, aptly named Requiem, even more exceptional are the following factors. Firstly, its location an astounding 10 billion light-years away adds to its cosmic grandeur. Secondly, this supernova belongs to the type Ia category, renowned for its consistency, making it an ideal “standard candle” for measuring cosmic distances.

The models predicted a delayed appearance of one of the supernova images, attributed to its path through the intense gravity of the cluster. Consequently, this image is projected to become visible to us only in the mid-2030s. Unfortunately, Requiem wasn’t discovered until 2019, after it had faded from view, preventing the gathering of sufficient data to accurately measure the Hubble constant.

In a serendipitous turn of events, scientists stumbled upon a second gravitationally lensed supernova within the same galaxy as Requiem, aptly named Supernova Encore. To ensure a comprehensive study, scientists actively monitor Encore using Webb images through a time-critical director’s discretionary program. Leveraging this multiply imaged supernova, the primary objective is to measure and verify the Hubble constant. Encore, classified as a type Ia supernova and therefore a standard candle, joins Requiem as the most distant pair of standard-candle supernova “siblings” ever discovered.

Scientists expressed their excitement, stating, “Supernovae are typically unpredictable, but in this case, we possess the knowledge of when and where to observe the final manifestations of Requiem and Encore. Infrared observations around 2035 will capture their last awe-inspiring display and provide a new and precise measurement of the Hubble constant.”



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