What Will Happen When The Sun Dies?
QUICK ANSWER
In about 5 billion years, the Sun will expand into a red giant, swelling to the orbit of Earth or beyond, swallowing Mercury and Venus. After shedding its outer layers as a planetary nebula, the Sun will collapse into a white dwarf about the size of Earth and slowly cool for trillions of years.
The Sun has about 5 billion more years before it runs out of hydrogen in its core. When that happens, the Sun will go through a dramatic series of changes, expanding into a red giant, shedding its outer layers, and finally collapsing into a white dwarf. None of this will happen quickly, but the end of the Sun's main sequence life will be one of the most dramatic events in the solar system's history.
When will the Sun die?
In about 5 billion years, give or take. According to NASA, the Sun is about halfway through its expected 10-billion-year main sequence lifetime. The Sun has been gradually getting brighter and will continue to do so as it ages. Long before its actual death, the Sun's brightness will make Earth uninhabitable (within about 1 billion years). The transition into a red giant won't happen until about 5 billion years from now, when the Sun finally exhausts the hydrogen in its core.
What happens during the red giant phase?
The Sun expands dramatically. When hydrogen runs out in the core, the core contracts and heats up, while the outer layers expand outward. The Sun will swell to many times its current size, possibly reaching past Earth's orbit. Mercury and Venus will almost certainly be swallowed; Earth may be too, or may escape by a thin margin. The red giant phase will last several hundred million years before the Sun burns through its remaining fuel.
What happens after the red giant phase?
The Sun sheds its outer layers and becomes a white dwarf. Once helium runs out in the core, the Sun isn't massive enough to fuse heavier elements. The outer layers will drift away into space, forming a planetary nebula (a glowing shell of expanding gas). What remains is the Sun's hot dense core, now exposed and called a white dwarf. White dwarfs are about the size of Earth but contain about half the Sun's original mass. They don't generate new energy; they simply cool slowly over trillions of years.
Does the Sun explode at the end?
No, it's not big enough. Only stars more massive than about 8 times the Sun's mass end their lives in supernovas. The Sun is far below that threshold. The red giant phase is dramatic but not explosive; the Sun will shed its outer layers gradually rather than catastrophically. The end result is a white dwarf, a small dense object that will fade slowly. Eventually the white dwarf may cool entirely into a cold black dwarf, though none exist yet because the universe isn't old enough.
The Sun has about 5 billion years before it begins to die. The red giant phase will dramatically reshape the inner solar system, likely engulfing Mercury and Venus and possibly Earth. After that, the Sun will shrink to a white dwarf and slowly fade. The transformation is unhurried but inevitable, the same fate awaiting all stars in the Sun's mass range.
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