A Bright Supernova in the Nearby Galaxy NGC 2403

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September 2, 2004: The explosion of a massive star blazes with the light of 200 million Suns in this NASA Hubble Space Telescope image. The arrow at top right points to the stellar blast, called a supernova. The supernova is so bright in this image that it easily could be mistaken for a foreground star in our Milky Way Galaxy. And yet, this supernova, called SN 2004dj, resides far beyond our galaxy. Its home is in the outskirts of NGC 2403, a galaxy located 11 million light-years from Earth. Although the supernova is far from Earth, it is the closest stellar explosion discovered in more than a decade.

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Q & A: Understanding the Discovery

1. 1. How often does a supernova explosion occur in a galaxy?




Every second, a star dies in a supernova explosion somewhere in our universe. That corresponds to a supernova blast occurring roughly every 100 years in a galaxy.

2. 2. What is the difference between a "Type I" and a "Type II" supernova?




A Type I supernova results from the explosion of a white dwarf, the collapsed hot core of a dead star. Gas from a companion star spills onto the white dwarf and piles up until an explosion occurs. A Type II supernova is the explosion of a single, massive star.

3. 3. Why did the star explode in a star cluster?




Massive stars like the one that became SN 2004dj typically form in open star clusters, which contain mostly young stars.