Supernova explosions are the most spectacular light shows seen in the universe since the big bang, and a recent one of a gigantic Wolf-Rayet star should shed new insight as to how these light shows are actually produced. Supernovae are so bright and powerful that they actually briefly outshine the entirety of their host galaxy. At least dozens of times more massive than the sun, the hot blue giant stars that explode in supernovae are short-lived and carry within them the elements that make all living things. However, for a long time, astronomers have been forced to study these powerful forces of nature indirectly. The recent explosion of a Wolf-Rayet star called SN 2013cu sheds far more direct evidence on supernovae throughout the cosmos, and for the first time allows for new insight into a supernova as it is actually occurring.
Wolf-Rayet stars are the most massive in the universe. They are 20 or more times heavier than the sun. Because these stars are so big, they exhaust their nuclear fuel very quickly and die young, in only a few million years, a very short period of time from the perspective of a star. This is contrasted with our own Sun, which has a life of about 10 billion years and the most common stars in the universe, red dwarves, which have lives lasting trillions of years.
Given the sheer amount of matter Wolf-Rayet stars contain, it was difficult for astronomers to gain insight as to exactly how they blew themselves apart, because their vision was often obscured, and Wolf-Rayet stars are very uncommon. They comprise far less than one percent of the universe’s stars.
However, a recent supernova of a Wolf-Rayet star known as SN 2013cu in the Bootes Constellation is offering valuable new insight into the lives of these stellar goliaths. Using the intermediate Palomar Transient Factory, scientists in Israel have seen a Wolf-Rayet supernova a mere hours after it occurred, giving an almost real-time insight into these powerful explosions.
The Wolf-Rayet star exploded in a Type IIb supernova, which ionized nearby molecules with ultraviolet light. Using this data, the astronomers were able to confirm the chemical composition of the star just before the explosion.
This observation shed light on the fact that Wolf-Rayet stars are directly responsible for at least some of these types of supernovae observed in the universe. A supernova of this nature occurs when the core of a massive star collapses in on itself and bounces outward, sending the rest of the star’s mass careening off into space. Whereas stars the size of the sun and smaller ultimately end their lives as dense white dwarves held up by the repulsion of their electrons, Wolf-Rayet stars are so massive that they leave behind either neutron stars, which are held up by the repulsion of their neutrons, or black holes.
However, because the explosions of these stars leave so much debris behind, it was hard to pinpoint which star caused what type of supernova. Some wondered whether or not stars of the Wolf-Rayet variety even exploded as supernovae or bypassed this phase and simply collapsed into black holes, almost as if disappearing without a trace. The observation of SN 2013cu now puts that theory to rest. Peter Nugent, the co-author of the study, remarked that the observation was the first time that it could be directly said that a Type IIb supernova occurred from the death of a specific Wolf-Rayet star.
The supernova of this Wolf-Rayet star now leads into questions as to whether or not this is typical. If it is, Avishay Gal-Yam, co-author of the study, said that new theories would need to be formulated to shed insight as to how black holes can form and still throw out enough material to make a supernova.
By Jordan Carpenter