What is a supernova?
A supernova is the powerful explosion of a star. For a short time it can outshine an entire galaxy, scattering elements such as iron and oxygen into space.
There are two main types. Some supernovas happen when a very massive star, at least about eight times the mass of the Sun, runs out of fuel. Its core collapses in less than a second and the outer layers are blasted away, often leaving behind a neutron star or a black hole. Others occur when a white dwarf in a pair of stars gains too much matter and explodes.
Supernovas are important for life. Many of the elements in our bodies and on Earth, including some of the iron in our blood and calcium in our bones, were made in stars and spread through space by such explosions. The shock waves can also squeeze clouds of gas and help new stars form.
Famous supernovas
In 1054, Chinese astronomers recorded a new star bright enough to see during the day for weeks. Its remains are the Crab Nebula. The last supernova seen with the naked eye in our galaxy was in 1604. The red giant Betelgeuse is expected to explode one day, but probably not for tens of thousands of years or more.
Did You Know?
Astronomers use one type of supernova as cosmic measuring sticks. Observations of them in the 1990s revealed that the expansion of the universe is speeding up.