Massive stars have a layered structure, with outer layers predominantly composed of lighter elements, progressively growing heavier until reaching the innermost iron core. This is the accepted theory, but observations of massive exploding stars – a phenomenon known as a supernova – had revealed only light elements. In a new study published today in Nature, an international team including Weizmann researchers discovered a new type of supernova: one that is rich in heavy elements – suggesting that the massive star, dubbed SN2021yfj, had somehow lost its outer layers while still “alive.”
To gain more information about the mysterious object, the team wanted to obtain its spectrum, which breaks down dispersed light into component colors, each of which represents a different element. By analyzing a supernova’s spectrum, scientists can determine which elements are present in the explosion.
Once the spectrum data was obtained, the researchers were amazed to discover that instead of helium, carbon, nitrogen, and oxygen typically found in other stripped supernovae, the spectrum of SN2021yfj was dominated by strong signals of silicon, sulfur, and argon.
“This star lost most of the material that it produced throughout its lifetime,” said lead author Dr. Steve Schulze. “So we could only see the material formed during the months right before its explosion. Something very violent must have happened to cause that.”
The scientists are currently exploring multiple scenarios, including interactions with a potential companion star, a massive pre-supernova eruption, or even unusually strong stellar winds. But, most likely, the team posits this mysterious supernova is the result of a massive star literally tearing itself apart. As the star’s core squeezes inward under its own gravity, it becomes even hotter and denser. The extreme heat and density then reignite nuclear fusion with such incredible intensity that it causes a powerful burst of energy that pushes away the star’s outer layers.
“Once we identified the spectral signatures of silicon, sulfur, and argon, it was clear this was a major step forward: Peering into the depths of a giant star helps us understand where the heavy elements come from,” said Prof. Avishay Gal-Yam, whose research group in Weizmann’s Particle Physics and Astrophysics Department focuses on understanding how the elements are formed in the universe. “Now it appears that the inner layers of giant stars are production sites for some of these important, relatively heavy elements.”