The Death of Stars

Supernova Stellar Death Earth Sun Red Image

When measuring a lifespan in millions, billions and even hundreds of billions of years, it may not seem likely, but stars do die. Eventually they stop pumping out energy and end their existence in a somewhat spectacular fashion, but waiting and watching for it to happen is not recommended.

A Look at the Death of Stars

A star’s lifespan is determined by its original mass and size. Earth scientists use solar radius and solar mass in measuring stars, units equal to the radius and mass of our life giving star, the Sun. The larger, and technically the more massive, a star, the shorter its over all life span is. The biggest of stars will last about a million years, while an average mass star, like our Sun, will last around ten billion (our Sun is about 5 billion years old now). Some very small stars can last hundreds of billions of years, but regardless of how long they last, all stars will eventually die.

How it Happens

Stars are giant balls of burning fuel, using hydrogen fusion to pump energy out into space. As the core burns up the available fuel, the star will cool. The outer layers expand and the star becomes dimmer. It will grow until it becomes what is known as a red giant or, in some cases, a red supergiant (depending on its size before it began its death throes.) This is the reason the very massive stars die more quickly, as the pressure put on the core makes the fuel burn faster.

What Happens Next?

There are three different final stages that a star will enter based on its initial mass. A star will either become a neutron star, a black dwarf, or a black hole. If a star starts out around the size of the Sun (and up to 1.5 solar masses) it will wind up a black dwarf; a star up to 3 solar masses is destined to become a neutron star, and any star larger than 3 solar masses is going to make it to the mysterious black hole stage.

For those headed towards the black dwarf stage, death is almost peaceful, for the star at least. Take the Sun, for example. It will grow to become a red giant, which means it will “eat” Mercury and Venus, and possibly Earth. Some theories are that Earth will be pushed back by the solar wind and attain a new orbit, but so close to the sun that all life will be extinguished. The Sun will eventually shrink as it cools. For stars over 3 solar masses, however, there is no “aging gracefully”. For them there is the supernova.

Supernova

Imagine collecting all the radiation that our Sun emits over its entire estimated lifetime, and then releasing it all at once. That is the amount of energy that a supernova emits. For stars much bigger than the Sun this is what happens to them after they become a red giant. After the supernova, a backlash occurs with the explosion collapsing in on itself, growing more and more dense until either a neutron star or a black hole forms.

Final Thoughts

Like in the circle of life and death on Earth, the death of a star is a healthy part of the life cycle of the universe, with the explosions of a supernova often being the catalyst of new star formation.