Two-speed galaxy, second supernova under the spotlight

Hey, space and galaxy lovers, get ready for a cosmic story that goes beyond expectations! In November 2023, NASA’s James Webb Space Telescope was doing its work and stumbled upon a massive cluster of galaxies called MACS J0138.0-2155. Sounds like a movie code name, doesn’t it? Now, grab your cup of space coffee because things get interesting, it turns out that this cluster, thanks to a gravitational trick of Albert Einstein’s called gravitational lensing, was warping and magnifying a distant galaxy called MRG-M0138. It is not just a light and shadow effect, but produces five different images of the same galaxy! As if posing for a cosmic selfie.

But here comes the first plot explosion, in 2019, astronomers dropped the bombshell on us that inside MRG-M0138 there was a supernova, a stellar explosion, as captured by the Hubble Space Telescope in 2016. Boom! Guess what? Another group of astronomers, reviewing James Webb images in 2023, discovers that seven years later there is another supernova in the same galaxy! Are they practicing for a cosmic show? Justin Pierel of NASA and Andrew Newman of the Carnegie Institution for Science have jumped into the fray. According to them, when a supernova explodes behind a gravitational lens, its light reaches Earth by different paths. Think of it as several trains leaving a cosmic station, all traveling to the same destination, but each taking its own route, this is not a speed competition, it is a parade of cosmic trains.

The 2016 supernova, nicknamed “Requiem,” is the star of the show. At 10 billion light years away, it’s like the rockstar of the universe. Moreover, it is of the same type that we use as a “standard candle” to measure cosmic distances; but wait, there’s more: one of the Requiem images is so delayed that it won’t appear until the mid-2030s. Even the future has tricks up its sleeve! But here comes the big revelation! We discover another supernova in the same galaxy as Requiem, and call it “Supernova Encore”; sounds like an epic sequel, right? We are following the show in real time and using the James Webb images, we will measure and confirm the Hubble constant.

Encore and Requiem are the most distant dynamic duo of standard-sail supernovae we have ever encountered. Supernovas are usually like surprise parties, but in this case, we know when and where to look for the grand finale of Requiem and Encore. In 2035, with our cosmic infrared glasses, we will capture its last hurrah and obtain a new and precise measurement of the Hubble constant. Space never ceases to amaze us, guys!