They use the second type of supernova (the kind involving white dwarfs) like a ruler, to measure distances in space. Scientists have learned a lot about the universe by studying supernovas. Space dust blocks our view of most of the supernovas within the Milky Way. Because the universe contains so many galaxies, astronomers observe a few hundred supernovas per year outside our galaxy. Astronomers believe that about two or three supernovas occur each century in galaxies like our own Milky Way. These spectacular events can be so bright that they outshine their entire galaxies for a few days or even months. Image credit: STScI How bright are supernovas? Eventually, this will cause the white dwarf to explode. In this illustration, a white dwarf pulls matter from a companion star. If one white dwarf collides with another or pulls too much matter from its nearby star, the white dwarf can explode. A white dwarf is what's left after a star the size of our sun has run out of fuel. Loll (Arizona State University)Ī second type of supernova can happen in systems where two stars orbit one another and at least one of those stars is an Earth-sized white dwarf. Astronomers and careful observers saw the supernova in the year 1054. The Crab Nebula is the leftover, or remnant, of a massive star in our Milky Way that died 6,500 light-years away. A supernova of a star more than about 10 times the size of our sun may leave behind the densest objects in the universe- black holes. Usually a very dense core is left behind, along with an expanding cloud of hot gas called a nebula. Imagine something one million times the mass of Earth collapsing in 15 seconds! The collapse happens so quickly that it creates enormous shock waves that cause the outer part of the star to explode! Gravity wins out, and the star suddenly collapses. When a massive star runs out of fuel, it cools off. What holds stars together? It’s a balance of gravity pushing in on the star and heat and pressure pushing outward from the star’s core. This outward push resists the inward squeeze of gravity. But the nuclear fuel burning in the star’s core creates strong outward pressure.
The star’s gravity tries to squeeze the star into the smallest, tightest ball possible. Heat generates pressure, and the pressure created by a star’s nuclear burning also keeps that star from collapsing.Ī star is in balance between two opposite forces. This produces tons of energy, so the center gets very hot. Massive stars burn huge amounts of nuclear fuel at their cores, or centers. This happens when a star at least five times the mass of our sun goes out with a fantastic bang! One type of supernova is caused by the “last hurrah” of a dying massive star.
Image credit: NASA/CXC/M.Weiss What causes a supernova? Each blast is the extremely bright, super-powerful explosion of a star.Īn illustration of one of the brightest and most energetic supernova explosions ever recorded. A supernova is the biggest explosion that humans have ever seen.
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