Webb discovers second lensed supernova in distant galaxy

In November 2023, the James Webb Space Telescope observed a giant galaxy cluster called MACS J0138.0-2155. Through the gravitational lensing effect first predicted by Albert Einstein, a distant galaxy named MRG-M0138 is distorted by the powerful gravity of the intervening galaxy cluster. In addition to distorting and magnifying the distant galaxy, the gravitational lensing effect caused by MACS J0138 produced five different images of MRG-M0138.

In 2019, astronomers announced the surprising discovery of a stellar explosion, or supernova, occurring inside MRG-M0138, as seen in images taken by NASA’s Hubble Space Telescope in 2016.

When another team of astronomers examined the 2023 Webb image, they were surprised to find a second supernova in the same galaxy seven years later. Justin Pierre (Einstein Fellow at NASA’s Space Telescope Science Institute) and Andrew Newman (Astronomer at the Carnegie Institution for Science) tell us more about the first-ever discovery of two gravitationally lensed supernovae in the same galaxy. Lots of information.

“When a supernova explodes behind a gravitational lens, its light takes several different paths to reach Earth. We can compare these paths to several trains leaving the station at the same time, all traveling at the same speed and heading to Same location. The trains travel different routes and don’t arrive at their destinations at the same time due to differences in trip length and terrain.”

“Similarly, astronomers see images of gravitationally lensed supernovae over the course of days, weeks, or even years. By measuring the differences in the timing of supernova images, we can measure the history of the universe’s expansion rate, known as the Hubble constant, which is today’s A major challenge in cosmology. The problem is that these multiplexed supernovae are extremely rare: fewer than a dozen have been detected so far.”

“In this small club, the 2016 supernova in MRG-M0138, named Requiem, stands out for several reasons. First, it is 10 billion light-years away. Second, this supernova may be related to The same type (Ia) used as a supernova. The ‘standard candle’ for measuring cosmic distances.”

“Third, models predict that one of the supernova images, delayed by its path through the cluster’s extreme gravity, will not be visible to us until the mid-2030s. Unfortunately, Requiem was not discovered until 2019, It was not discovered until much later. When it disappeared from view, it was impossible to collect enough data to measure the Hubble constant.”

“Now we have discovered a second gravitationally lensed supernova in the same galaxy as Requiem, which we call supernova Encore. Encore was discovered by accident and we are now actively tracking it through a time-sensitive Director’s Discretionary Program Supernova going on.”

“Using these Webb images, we will measure and confirm the Hubble constant based on this multiple-image supernova. Encore was confirmed to be a standard candle supernova, or Type Ia supernova, making Encore and Requiem the most distant standard pair to date. Candlelight supernova ‘siblings’ ever discovered.”

“Supernovae are usually unpredictable, but in this case we know when and where we will see the final appearance of the Requiem and Encore. Infrared observations around 2035 will capture their final cheers and a new precise measurement of the Hubble constant.”