Scientists have finally identified the mysterious source of X-ray emissions at the center of our galaxy’s youngest supernova: Inside the remains of Cassiopeia A sits a baby neutron star surrounded by a thin layer of carbon.

“This discovery helps us understand how neutron stars are born in violent supernova explosions,” astrophysicist Craig Heinke of the University of Alberta said in a press release. “This neutron star was born so hot that nuclear fusion happened on its surface, producing a carbon atmosphere just 10 centimeters thick.”