What is 10 miles across, but powers an explosion brighter than the Milky Way?

Right now, astronomers are viewing a ball of hot gas billions of light years away that is radiating the energy of hundreds of billions of suns. At its heart is an object a little larger than 10 miles across. And astronomers are not entirely sure what it is. If, as they suspect, the gas ball is the result of a supernova, then it’s the most powerful supernova ever seen.

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What is 10 miles across, but powers an explosion brighter than the Milky Way?