Stars are formed out of great clouds in outer space called nebulae or nebulas. Stars shine by light produced through nuclear fusion in their cores, as hydrogen is converted into helium at a temperature of millions of degrees. In time the hydrogen is used up, and the star begins to die. The less massive the star, the longer it lives, the more massive, the shorter the lifespan. There are small, cool red dwarf stars shining today that burned when the Universe was young. Our own sun has been producing light for five billion years, and will shine for another five billion years. Blue giant stars will only last for a few hundred million years at most – the more massive the star, the more profligate the energy and matter loss. When stars like our sun die, they don’t explode; they just shrink, heat up and brighten becoming a red giant star, then collapse down to a white dwarf, and then slowly go out. But the biggest, most massive stars explode as supernovas, or implode to become black holes.