Our Sun, the star at the center of our solar system, provides the light and heat that make life possible on Earth. Like all stars, the Sun has a life cycle. While the idea of the Sun “exploding” might come to mind, its end will be a more gradual, yet dramatic, transformation.
The Sun’s Stellar Evolution, Not a True Explosion
The Sun will not end its life in a supernova, a spectacular explosion reserved for stars at least eight times more massive. Our Sun lacks the mass for such a cataclysmic event. Instead, it will follow a predictable path of stellar evolution, characteristic of stars with its initial mass.
The Sun is currently a “main-sequence” star, a stable phase where it fuses hydrogen into helium in its core. This fusion creates outward pressure, balancing gravity and maintaining the Sun’s size and luminosity. This stable period represents the longest phase of a star’s life. As hydrogen fuel in the core depletes, this balance will shift, initiating the next stages of stellar evolution.
The Red Giant Phase and Its Impact on Our Solar System
In approximately 5 billion years, the Sun will exhaust the hydrogen fuel in its core. Its core will then contract under gravity, increasing its temperature and density. This heat will ignite hydrogen fusion in a shell around the core. The energy from this shell burning will cause the Sun’s outer layers to expand significantly, transforming it into a red giant.
During this red giant phase, the Sun’s outer atmosphere will swell immensely, expanding to over 200 times its current radius. It will engulf the orbits of Mercury and Venus, and likely Earth. Even if Earth avoids direct engulfment, its surface will become uninhabitable long before due to the extreme heat and increased luminosity. The Sun’s luminosity will increase thousands of times, scorching the planet and evaporating its oceans.
The White Dwarf and Planetary Nebula Stage
After the red giant phase, the Sun’s outer layers will be shed into space. This expelled material will form a glowing shell of gas known as a planetary nebula. This process is a relatively peaceful event, unlike the explosive end of more massive stars.
What remains of the Sun will be its core, contracting into a dense white dwarf. A white dwarf is incredibly dense, with a mass comparable to the Sun’s packed into an Earth-sized volume. It no longer undergoes nuclear fusion, shining only from residual heat. Composed primarily of carbon and oxygen, it will slowly cool over trillions of years, fading into obscurity.
The Grand Timeline of the Sun’s Life
The Sun formed approximately 4.6 billion years ago from a vast cloud of gas and dust, spending this time in its main-sequence phase, steadily fusing hydrogen in its core. This period of stability will continue for roughly another 5 billion years.
Following this, the Sun will enter its red giant phase, lasting for approximately 0.5 to 1 billion years. Finally, it will settle into its white dwarf stage, slowly cooling over trillions of years. The outer planets of our solar system will likely survive the red giant phase, but their orbits will expand due to the Sun’s mass loss. Over tens of billions of years, even these distant planets might eventually be ejected from the solar system due to gravitational interactions with passing stars.