A few thousand million years from now, the Sun will run out of hydrogen at its center. Then the nuclear reactions will spread outwards into the region surrounding the Sun’s core. With more hydrogen to burn, the Sun will produce more energy, and it will swell up into a red giant star.
As the Sun gets bigger and brighter, the Earth will be roasted to a cinder. When the sun has swollen to its largest, perhaps 100 times the size it is now, its outer layers will drift off into space, like a celestial smoke ring. The core of the former red giant will be left behind as a small condensed star called a white dwarf.