A light year is unit of distance. It is how far light travels in one year. Light is really fast; in one year it travels about 5,878,786,100,000 miles (almost 6 trillion). The other cool thing is that because it takes time for the light to get to us, we are looking back in time. A supernova is the explosive death of a large star as it runs out of fuel. This supernova was part of the first generation of supernova ever.
Source- UC Irvine
Image Credit- NASA/Swift/Skyworks Digital/Dana Berry