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How long does a supernova stay bright after exploding?
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Supernova
Composite image of Kepler's Nova, or Kepler's Supernova, taken by the Chandra X-ray Observatory.
A supernova is characterized by a rapid, tremendous increase in brightness that typically lasts for a few weeks. Following this peak, the star undergoes a slow decline in brightness over the subsequent months.12
While the initial outburst is brief, the event marks a cataclysmic end to the star's active lifetime. The resulting supernova remnant—the cloud of debris ejected during the explosion—continues to expand and evolve for thousands of years, radiating energy as it interacts with the surrounding interstellar medium.12