The popular image of the Sun ending its life in a spectacular, instantaneous explosion is a misconception. The Sun, currently a G-type main-sequence star, is sustained by the fusion of hydrogen into helium at its core, a process that has kept it stable for billions of years. When that fuel supply runs out, the star will undergo a series of gradual transformations. The ultimate fate of our star is not a violent catastrophe, but rather a slow, immense inflation followed by a quiet fade. This less violent conclusion is dictated by the Sun’s relatively low mass.
Why the Sun Will Not Explode
The Sun’s relatively modest mass is the factor that prevents it from ending its life in a supernova explosion. A true core-collapse supernova (Type II) occurs only in stars with an initial mass of at least eight to ten times that of the Sun. These massive stars possess the gravitational force necessary to fuse elements all the way up to iron in their cores. Once an iron core forms, the star can no longer generate outward energy pressure, leading to a catastrophic implosion and subsequent immense explosion. The Sun lacks this necessary mass threshold and will instead follow the less dramatic evolutionary path reserved for low-mass stars, concluding its life by slowly shedding its outer layers.
The Red Giant Transformation
The Sun’s stable life will end in approximately five billion years when the hydrogen fuel in its core is exhausted. Without the outward pressure from core hydrogen fusion, gravity will cause the inner helium core to contract and heat up. This rising temperature will ignite a shell of fresh hydrogen surrounding the core, triggering hydrogen shell burning.
The energy output from this new fusion shell is far more intense than the previous core fusion, causing the Sun’s outer layers to expand dramatically and cool. As the star’s radius swells, its surface temperature will drop, shifting its color from white-yellow to a deep reddish-orange. This immense stellar state is known as the Red Giant phase, during which the Sun’s radius will grow to over 200 times its current size.
Earth’s End During Solar Expansion
The Sun’s transformation into a Red Giant will set into motion the destruction of the inner Solar System. Long before the star reaches its maximum size, increased luminosity will push the habitable zone outward, causing a runaway greenhouse effect on Earth. Within about a billion years, the intense heat will boil away the planet’s oceans, turning Earth into a scorching, arid world.
As the Sun’s outer layers continue to expand, they will physically engulf the orbits of Mercury and Venus, incinerating them. The Sun will also lose a significant amount of mass during this phase, which will weaken its gravitational pull and cause Earth’s orbit to expand. Current models indicate that the Sun’s expanded edge will reach or slightly surpass Earth’s current orbital radius, meaning Earth will likely be swallowed and vaporized by the star’s atmosphere. If the planet avoids complete engulfment, the drag from the solar gas will cause its orbit to decay, sending the planet spiraling inward to be dispersed.
The White Dwarf Remnant
After the Red Giant phase, the Sun will shed its outer layers into space. This material will form a vast, brightly illuminated cloud of gas and dust known as a planetary nebula. The remaining core will then collapse into a stellar remnant called a White Dwarf.
This White Dwarf will be incredibly dense, packing about half of the Sun’s original mass into a sphere approximately the size of Earth. It is prevented from collapsing further by electron degeneracy pressure, which acts as a repulsive force between electrons. The White Dwarf will consist primarily of inert carbon and oxygen, radiating residual heat from its formation. Over trillions of years, this stellar corpse will slowly cool and fade until it becomes a cold, dark body known as a Black Dwarf.