Scientists have just seen the biggest star explosion observed to date. Star explosions are often called supernovas.

The supernova was up to 100 times larger than our sun and happened in a galaxy far away.

It released two times as much energy as any star explosion ever observed and happened about 4.6 billion light years from Earth, scientists said. A light year is the distance light travels in one year, which is 9.5 trillion kilometers.

galaxy - n. any one of the very large groups of stars that make up the universe

theory - n. an idea or set of ideas that is intended to explain facts or events

astrophysicist - n. a scientist who studies the physical and chemical properties and structures of stars, planets and other objects in outer space

gravity - n. the natural force that tends to cause physical things to move towards each other

collision - n. a crash in which two or more things or people hit each other

pulsational - adj. a periodically recurring increase and decrease of a quantity, such as pressure, volume or voltage

astronomy - n. the scientific study of stars, planets, and other objects in outer space