Learn more about what happens when stars explode.

This 1991 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 15,000 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 9,000 to 25,000 miles (15,000 to 40,000 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.

Star Fusion

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.

When a star's core contracts to a critical point, a series of nuclear reactions is unleashed. This fusion staves off core collapse for a time—but only...

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