Normally a star will only explode once, if at all. However the star named iPTF14hls has gone supernova and astronomers believe it may have done so twice before. In an article from Science News written by Lisa Grossman, this is discussed in detail. Astronomers believe that it could be due to the burning of antimatter in its core or possibly a new concept in physics entirely. Data collected between late 2014 and mid 2016 showed that the star was bright for an excess of 600 days and is apparently just now showing signs of dying down, however the star was thought to have already been in the process of dying down when it was discovered in 2014 so it might have been in this process for a much longer time. Some theories suggest that some stars that are about 95 to 130 times the mass of the sun may explode numerous times. Stars such as these burn so hot that they are able to convert gamma rays, where their high energy helps prevent the star from going supernova, into forms of matter such as election and positrons. After the matter is produced, it then recombines and forms gamma rays, preventing the star from exploding.
In my opinion, this discovery is amazing and incredibly intriguing. The idea that a star could go supernova numerous times is mind boggling awesome to me. However, the article later states that Stanford Woosley, a theoretical physicist of the University of California of Santa Cruz, believes that a magnetar, which is a highly magnetized rapidly rotating stellar corpse could possibly glow for around two year.
The following image shows a graph depicting the relationship between the days since discovery and the brightness (in billions of suns) and the top line is the track of the brightness of the star discussed above.