College College Space and Planetary Sciences

Colliding Stars and Supernovas

Two stars are on collision course, and we will be able to see the resulting supernova without a telescope in 2022.

Supernovas are fascinating phenomena that have been observed by humans since the beginning of time. People came up with their own conclusions as to what these cosmic events were, but as astronomy developed, supernovas became known as the death of stars and as the birth of new stars. The most recent observation of supernovas with the naked eye happened in the year 1604. Johannes Kepler, a German astronomer, noticed that a new star had appeared in the sky and began making observations about it. This star was brighter than any star in the sky, including the North star (1). Now, well in about four years, we will be able to see what Kepler saw back in the day. A new supernova will be visible with our own eyes in 2022 with the collision of two stars. But let’s talk about the basics of supernovas first.

Supernovas are typically classified as either a Type I or Type II supernova. Type I supernovas exhibit a sharp initial spike of luminosity that dies down rapidly, which means that there is a lack of hydrogen within the observed spectrum of the supernova. Type can further subdivide into Types Ia, Ib, and Ic. Type Ia supernovas have a strong presence of silicon, which might mean the doomed star had or accreted silicon sometime in its lifecycle. Type Ib shows a strong presence of helium within the spectrum and Type Ic are all other high velocity explosions. In most cases, Type I supernova occur only in white dwarf stars as they are high energy stars packed into a small radius. There are two ways this type of supernova can occur: one way is for the white dwarf to simply collapse on itself, and the other is for the white dwarf to accrete mass from a nearby star (most likely in a binary system). The other type of supernova is the Type II, which typically occurs in much more massive stars. In this type, the star becomes so massive that it collapses on itself and blows away its gases deep into space. On a light curve, the luminosity of the explosion still has the same spike as in the Type I explosion, but there is a “plateau” in the middle of the graph that shows spread of the gases (2).

In 2022, we will most likely be looking at a Type I supernova since the merging stars in question are in a binary system named KIC 9832227 (what a creative name!). In fact, they are so close to each other that they are beginning to merge. The proximity of the stars accelerates the accretion process between the two similar stars so much so that it appears the two stars are colliding. One example that scientists looked at was the supernova that happened in the system V1309 Scorpii in 2008. This was a supernova caused by a merger between two stars in the system. Leading up to the explosion, the system was getting brighter and brighter until the supernova happened. Unfortunately, this supernova was not visible to the naked eye, but scientists are confident that KIC 9832227 is experiencing the same increases in brightness. Scientists are predicting that this supernova will be as bright as the North star in the night sky and located somewhere in the constellation Cygnus (3).





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