Two images of the Stingray Nebula, located in the direction of the southern constellation Ara – or the Altar – captured 20 years apart by NASA’s Hubble Space Telescope. The image on the left was taken in March 1996, while the image on the right was captured in January 2016.NASA/ESA/Bruce Balick/Martín Guerrero/Gerardo Ramos-Larios
Stars are rather patient. They can live for billions of years, and they typically make slow transitions – sometimes over many millions of years – between the different stages of their lives.
So when a previously typical star’s behavior rapidly changes in a few decades, astronomers take note and get to work.