When the sun runs out of fuel what will it become?

When the Sun runs out of fuel, it will enter the red giant phase, expanding significantly and engulfing the inner planets, possibly including Earth. After shedding its outer layers, it will leave behind a hot core known as a white dwarf, which will gradually cool and fade over billions of years. Eventually, it will become a cold, dark remnant, often referred to as a black dwarf, though this stage is theoretical as the universe is not old enough for any black dwarfs to currently exist.