Small explosion, big explosion

Before exploding as an impressive supernova, some large stars go through a sort of smaller "sub-explosion", throwing significant portions of their mass into space

Before exploding as an impressive supernova, some large stars go through a sort of smaller "sub-explosion", throwing significant portions of their mass into space. Although this peculiar behavior has been predicted by several theoretical models, and although there is evidence to suggest its existence, direct observations of such subexplosions are extremely rare.

In a new study, a team of scientists led by Dr. Eran Ofek from the Weizmann Institute of Science was able to observe an explosion that occurred a short time - only one month - before the supernova of a massive star.
The findings, recently published in the scientific journal Nature, help to clarify the chain of events leading to the occurrence of a supernova, and provide insights into the processes that take place in the cores of large and massive stars as they approach the end of their lives.

Dr. Ofek, from the Department of Particle Physics and Astrophysics, is taking part in an international program for the study of supernovae (PTF) at the Plummer Observatory in California, led by Prof. Shri Kulkarni from the California Institute of Technology. The members of the research team from Israel, the UK and the USA asked to check whether the sub-explosions actually precede supernovas, and this through a scan of observations made at the Plumer Observatory prior to supernova events.

Dr. Ofek and his team did discover such a sub-explosion about a month before the occurrence of a supernova. The timing of the explosion, and the data on the amounts of material released during it, helped scientists to verify a certain theoretical model, which predicted sub-explosion events of this kind. Statistical analysis showed that the chance that the supernova event and the sub-explosion are not related to each other is only one tenth of a percent.

The exploding star, which ended its life as a type IIn supernova, began its journey as a massive star - at least eight times heavier than our Sun. As such a star ages, the internal nuclear fusion processes that enable its continued existence produce heavier and heavier elements, until most of the core is made of iron. At this point, the heavy core quickly collapses inward, and the star explodes.

According to Dr. Ofek, the intensity of the sub-explosion, and the mass of the material thrown into space, indicate that the source of the energy is in the processes that took place in the core of the star. The energy was transferred from the star's core directly to its surface using acoustic waves (similar to sound waves). The scientists believe that further studies will show that such sub-explosions are common in type IIn supernovae.

Also participating in the study were Prof. Avishai Gal-Yam, Dr. Ofer Yaron and Yair Hakabi from the Department of Particle Physics and Astrophysics at the Weizmann Institute, and Prof. Nir Shabiv from the Hebrew University of Jerusalem.
The scientific article: