Massive stars end their lives in an explosion called a supernova. Understanding the processes the star goes through in the final stages of its life, leading to a supernova, and understanding the explosion process itself, are some of the key questions in the field of astrophysics. The fact that we do not know in advance when and where such an explosion is going to occur makes it even more difficult to investigate this phenomenon. However, today we are able to discover a large number of supernovae every night through various dedicated projects. The detection capability has greatly improved in recent years and today we can detect supernovae only a few hours after the explosion!

Supernova SN2013fs was discovered by Palomar Transient Factory's supernova search project three hours after the explosion. Early detection made it possible to gather more information with advanced telescopes such as the Keck optical telescope that provided spectra for several hours after discovery. These early spectra revealed the existence of a very high-density gas that is very close to a supernova (10 ^ 15 cm) and will be ionized by the flash of light from the explosion itself. The spectral signatures of the gas disappeared several days after discovery, leading to the conclusion that around the supernova there is a thin, dense shell of gas that is completely swept away after several days by the material blown up in the explosion. Late radio observations have confirmed the speculation that this is indeed a thin, but massive, shell of matter around a supernova.

Massive stars lose mass throughout their lives, which enriches their immediate environment with low-density gas. The discovery of such a dense gas shell near the exploding star thus reveals that massive stars undergo dynamic processes that cause the stars to shed much of their material at once during the last year of their lives. These dynamic processes are not yet fully understood and there are several theories on the subject. Understanding these processes is critical to understanding the processes that take place on "dying" stars leading to a supernova.

The results of this study were recently published in an article in Nature Magazine (the article was written by a team of researchers from various universities in Israel and around the world, led by Dr. Ofer Yaron of the Weizmann Institute and in collaboration with Dr. Assaf Harash of the Hebrew University).