A Type Ia supernova named Encore is the second multiply-imaged supernova detected in MRG-M0138, a galaxy around 10 billion light-years away in the constellation of Cetus.
In November 2023, astronomers using the NASA/ESA/CSA James Webb Space Telescope observed a massive cluster of galaxies called MACS J0138.0-2155.
Through the gravitational lensing effect, the MRG-M0138 galaxy appears warped by the powerful gravity of the intervening galaxy cluster.
In addition to warping and magnifying the distant galaxy, the gravitational lensing caused by MACS J0138.0-2155 produces five different images of MRG-M0138.
In 2019, astronomers announced the surprising discovery of a supernova within MRG-M0138, as seen in images from the NASA/ESA Hubble Space Telescope taken in 2016.
When another group of astronomers examined the newest Webb images, they were astonished to find that seven years later, the same galaxy is home to a second supernova.
“When a supernova explodes behind a gravitational lens, its light reaches Earth by several different paths,” said Dr. Justin Pierel from the Space Telescope Science Institute and Dr. Andrew Newman from the Observatories of the Carnegie Institution for Science.
“We can compare these paths to several trains that leave a station at the same time, all traveling at the same speed and bound for the same location.”
“Each train takes a different route, and because of the differences in trip length and terrain, the trains do not arrive at their destination at the same time.”
“Similarly, gravitationally lensed supernova images appear to astronomers over days, weeks, or even years.”
“By measuring differences in the times that the supernova images appear, we can measure the history of the expansion rate of the Universe, known as the Hubble constant, which is a major challenge in cosmology today.”
“The catch is that these multiply-imaged supernovae are extremely rare: fewer than a dozen have been detected until…
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