Why does a supernova exploded

When stars are especially large, the core collapses into a black hole. Otherwise, the core becomes an ultra-dense neutron star. Another type of supernova, called a thermal runaway supernova, can occur when two stars orbit each other, and one or both of those stars is a white dwarf. White dwarfs are the remains of a star roughly the size of our Sun when it runs out of fuel.

If the stars in one of these binary systems collide, or if one of the white dwarfs absorbs enough matter from the other star, the white dwarf can become a supernova. Through its Nuclear Physics program, the Department of Energy Office of Science supports research into the fundamental nature of matter. That includes how matter — including the elements — is created and the role of supernovae in that process. Image credit: STScI. These spectacular events can be so bright that they outshine their entire galaxies for a few days or even months.

They can be seen across the universe. Not very. Astronomers believe that about two or three supernovas occur each century in galaxies like our own Milky Way. Because the universe contains so many galaxies, astronomers observe a few hundred supernovas per year outside our galaxy. Space dust blocks our view of most of the supernovas within the Milky Way. Scientists have learned a lot about the universe by studying supernovas. They use the second type of supernova the kind involving white dwarfs like a ruler, to measure distances in space.

Stars generate the chemical elements needed to make everything in our universe. At their cores, stars convert simple elements like hydrogen into heavier elements. These heavier elements, such as carbon and nitrogen, are the elements needed for life.

This image shows a small portion of the Cygnus Loop supernova remnant. The formation shown here marks the outer edge of an expanding blast wave from a colossal stellar explosion that occurred about 15, years ago. The blast wave slams into clouds of interstellar gas, causing it to glow and revealing information about the composition of the gas.

Some stars burn out instead of fading. These stars end their evolutions in massive cosmic explosions known as supernovae. When supernovae explode, they jettison matter into space at some 9, to 25, miles 15, to 40, kilometers per second. These blasts produce much of the material in the universe—including some elements, like iron, which make up our planet and even ourselves.

Heavy elements are only produced in supernovae, so all of us carry the remnants of these distant explosions within our own bodies. Supernovae add enriching elements to space clouds of dust and gas, further interstellar diversity, and produce a shock wave that compresses clouds of gas to aid new star formation.

But only a select few stars become supernovae. Many stars cool in later life to end their days as white dwarfs and, later, black dwarfs. But massive stars, many times larger than our own sun, may create a supernova when their core's fusion process runs out of fuel. Star fusion provides a constant outward pressure, which exists in balance with the star's own mass-driven, inward gravitational pull.

When fusion slows, outbound pressure drops and the star's core begins to condense under gravity—becoming ever denser and hotter. To outward appearances, such stars begin growing, swelling into bodies known as red supergiants. But at their cores, shrinking continues, making a supernova imminent. For a star to explode as a Type II supernova , it must be at several times more massive than the sun estimates run from eight to 15 solar masses.

Like the sun, it will eventually run out of hydrogen and then helium fuel at its core. However, it will have enough mass and pressure to fuse carbon. Here's what happens next:. What's left is an ultra-dense object called a neutron star , a city-sized object that can pack the mass of the sun in a small space.

There are sub-categories of Type II supernovas, classified based on their light curves. Both types have the signature of hydrogen in their spectra. Stars much more massive than the sun around 20 to 30 solar masses might not explode as a supernova, astronomers think. Instead they collapse to form black holes.

Type Ia supernovae are generally thought to originate from white dwarf stars in a close binary system. As the gas of the companion star accumulates onto the white dwarf, the white dwarf is progressively compressed, and eventually sets off a runaway nuclear reaction inside that eventually leads to a cataclysmic supernova outburst.

Astronomers use Type Ia supernovas as " standard candles " to measure cosmic distances because all are thought to blaze with equal brightness at their peaks.