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Something new in the sky

Around 500 million light-years away in the constellation Sculptor lies a rather peculiar looking galaxy, known as the Cartwheel galaxy. It was once a normal spiral galaxy that underwent a head-on interaction with a smaller companion galaxy several million years ago, giving it its signature cartwheel appearance. But there are other curious things about this object. This video blinks between two images: one captured in December 2021 with ESO’s New Technology Telescope (NTT) and one taken in August 2014 by the Multi Unit Spectroscopic Explorer (MUSE) mounted on ESO’s Very Large Telescope (VLT). The NTT image shows something interesting in the lower left corner: a supernova.

This event, called SN2021afdx, is a type II supernova, which occurs when a massive star reaches the end of its evolution. Supernovae can cause a star to shine brighter than its entire host galaxy and can be visible to observers for months, or even years — a blink of an eye on astronomical timescales. Supernovae are one of the reasons astronomers say we are all made of stardust: they sprinkle the surrounding space with heavy elements forged by the progenitor star, which may end up being part of later generations of stars, the planets around them and life that may exist in those planets.

Detecting and studying these unpredictable events requires international collaboration. The first time SN2021afdx was spotted was in November 2021 by the ATLAS survey, and it was then followed up by ePESSTO+, the advanced Public ESO Spectroscopic Survey for Transient Objects. ePESSTO+ is designed to study objects that are only in the night sky for very short periods of time, such as this supernova. It does this by using the EFOSC2 and SOFI instruments on the NTT, located at ESO's La Silla Observatory in Chile. EFOSC2 not only took this beautiful image, but also spectra that allowed the PESSTO team to identify this event as a type II supernova.