Are ghosts real? Spooky figures in a haunted house, maybe not. But if you’re looking for energy left behind after death, you may want to turn your gaze to the stars. Stars may not be conventionally “alive,” but they do have a lifecycle and part of that lifecycle includes death. In rare cases, that death releases a spectacular amount of energy in a supernova explosion.
What does stellar death look like?
Stars are considered active when they are producing and emitting energy. Much of this energy is in the form of heat, causing them to glow brightly in the night sky. All of this energy is produced in the core of the star, creating great pressure outward.
This outward pressure is balanced by gravity holding the star together. When the star runs out of gas, it cools and the gravitational force wins out, collapsing the star. What happens next depends on the mass of the star.
What causes a supernova?
Only high-mass stars (10 or more times more massive than our Sun) end their life as a supernova. These massive stars are left with only iron in their cores – an incredibly compact and stable element. No longer producing energy, the star begins the final stage of gravitational collapse. The temperature in the core of the star rises to over 1,000 billion degrees Fahrenheit!
As the star collapses, the iron atoms are crushed together, but only for so long. The repulsive force between the nuclei is stronger than gravity and within seconds, everything explodes out in a shock wave. This is a called a core-collapse supernova explosion.2
What do we see?
Initially, we see an explosion. These are some of the brightest explosions known anywhere in the universe, often outshining the rest of the galaxy. Although we think supernovae only occur once or twice per century in a galaxy, astronomers see hundreds of them every year from distant galaxies.
After this explosive death, a very dense core is left behind, along with an expanding cloud of hot gas called a nebula. This gas contains different materials that are excited when successive shock waves roll through at over 12 million mph, lighting it up in brilliant colors. This is called a supernova remnant, which is often the subject of many spectacular photographs. One of the most famous supernova remnants is the Crab Nebula.
How long do they last?
As the gas moves away from the center of the dead star, it will slowly lose energy, fading out over time. It may fade faster if it encounters other gas, and then some of the energy goes into moving the new gas or trying to heat it up.
As it fades, it will also change shape. The gas drifts outward and can be influenced by stellar winds. Sometimes, aftershocks will create new bubbles of gas that rush to catch up. All of this depends on how much energy was in the star to begin with.
However, this is a slow process. Supernova remnants can take anywhere between tens of thousands to one hundred thousand years to fade out entirely. These spectacular ghosts are here to stay.
Interested in learning more about these stellar ghosts? Check out the resources below:
Info about types of supernova remnants
Lifecycle of stars
Walk through a supernova remnant in virtual reality
1Apparent size is how large an object appears to us in the sky, rather than the actual physical size of the object.
2There are a few different types of supernovae, and core-collapse is just one type.
Acknowledgements:
Thanks to Madison Smith for double checking my knowledge of supernovae!
Edited by Lana Ruck and Dan Myers
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