How Long Do Stars Live?

a star cluster with massive stars.
The star cluster Pismis 24, located in the heart of a nebula in the constellation Scorpius, is home to a number of very massive stars, including Pismis 24-1 (the brightest star in the center of this image). ESO/IDA/Danish 1.5/ R. Gendler, U.G. Jørgensen, J. Skottfelt, K. Harpsøe

The universe is made up of many different types of stars. They may not look different from each other when we're looking into the heavens and simply see points of light. However, intrinsically, each star is a bit different from the next one and each star in the galaxy goes through a lifespan that makes a human's life look like a flash in the dark by comparison. Each one has a specific age, an evolutionary path that differs depending on its mass and other factors. One area of study in astronomy is dominated by the search for an understanding of how stars die. This is because a star's death plays a role in enriching the galaxy after it's gone.

Edited and updated by Carolyn Collins Petersen.

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The Life of a Star

Alpha Centauri
Alpha Centauri (left) and its surrounding stars. This is a main sequence star, just as the Sun is. Ronald Royer / Getty Images

To understand the death of a star, it helps to know something about its formation and how it spends its lifetime. This is true particularly since the way it forms influences its end game.

Astronomers consider that a star begins its life as a star when nuclear fusion commences in its core. At this point it is, regardless of mass, considered a main sequence star. This is a "life track" where the majority of a star's life is lived. Our Sun has been on the main sequence for about 5 billion years, and will persist for another 5 billion years or so before it transitions to become a red giant star. 

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Red Giant Stars

Red Giant Star
A red giant star is one step in a star's long lifetime. Günay Mutlu / Getty Images

The main sequence doesn't cover the star's entire life. It's just one segment of stellar existence, and in some cases, it's a comparatively short part of the lifetime.

Once a star has used up all of its hydrogen fuel in the core, it transitions off the main sequence and becomes a red giant. Depending on the mass of the star, it can oscillate between various states before ultimately becoming either a white dwarf, a neutron star or collapse in on itself to become a black hole. One of our nearest neighbors (galactically speaking), Betelgeuse is currently in its red giant phase and is expected to go supernova at any time between now and the next million years. In cosmic time, that's practically "tomorrow". 

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White Dwarfs and the End of Stars Like the Sun

White Dwarf
Some stars lose mass to their companions, as this one is doing. This accelerates the star's dying process. NASA/JPL-Caltech

When low-mass stars like our Sun reach the end of their lives, they enter the red giant phase. This is a bit of an unstable phase. That's because ​for much of its life, a star experiences a balance between its gravity wanting to suck everything in and the heat and pressure from its core wanting to push everything out. When the two are balanced, the star is in what's called "hydrostatic equilibrium." 

In an aging star, the battle gets tougher. The outward ​radiation pressure from its core eventually overwhelms the gravitational pressure of material wanting to fall inward. This lets the star expand farther and farther out to space.

Eventually, after all the expansion and dissipation of the outer atmosphere of the star, all that is left is the remnant of the star's core. It's a smoldering ball of carbon and other various elements that glows as it cools. While often referred to as a star, a white dwarf is not technically a star as it does not undergo nuclear fusion. Rather it is a stellar remnant, like a black hole or a neutron star. Eventually, it is this type of object that will be the sole remains of our Sun billions of years from now.

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Neutron Stars

Neutron star
NASA / Goddard Space Flight Center

A neutron star, like a white dwarf or black hole, is actually not a star but a stellar remnant. When a massive star reaches the end of its life it undergoes a supernova explosion. When that occurs, all the outer layers of the star fall in on the core and then bounce off in a process called "rebound." The material blasts away to space, leaving behind an incredibly dense core.

If the material of the core is packed together tightly enough, it becomes a mass of neutrons. A soup-can full of neutron star material would have about the same mass as our Moon. The only objects known to exist in the universe with a greater density than neutron stars are black holes.

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Black Holes

Black hole
This black hole, in the center of the galaxy M87, is ejecting a stream of material out from itself. Such supermassive black holes are many times the mass of the Sun. A stellar mass black hole would be much smaller than this, and much less massive, since it's made from the mass of only one star. NASA

Black holes are the result of very massive stars collapsing in on themselves due to the massive gravity they create. When the star reaches the end of its main sequence life cycle, the ensuing supernova drives the outer part of the star outward, leaving only the core behind. The core will have become so dense and so jam-packed that it's even more dense than a neutron star. The resulting object has a gravitational pull so strong that not even light can escape its grasp.