A rare glimpse of a star before it exploded in a fiery supernova looks nothing like astronomers expected, a new study suggests.

Images from the Hubble Space Telescope reveal that a relatively cool, puffy star ended its life in a hydrogen-free supernova. Until now, supernovas without hydrogen were thought to originate only from extremely hot, compact stars.

The discovery “is a very important test case for stellar evolution,” says Sung-Chul Yoon, an astrophysicist at Seoul National University in South Korea, who was not involved in the work. Theorists have some ideas about how massive stars behave right before they blow up, but such hefty stars are scant in the local universe and many are nowhere near ready to go supernova, Yoon says. Retroactively identifying the star responsible for a supernova provides an opportunity to test scenarios of how stars evolve right before exploding.