The sun's properties (luminosity, size, and temperature) have not changed much over the last 4.6 billion years. what do you think will eventually happen to the sun?

The answer is; The sun will turn into a red giant

This occurs as the hydrogen fuel in the fusion core of the sun begins to deplete. When the hydrogen fuel is depleted, the star begins to collapse on itself due to gravity. This pressure causes the heavier helium to begin fusing in the area around the core.  The stars begin to heat up again producing enough energy to push out the outer shells of the star. This causes the star to expand. The outer shells become less hot hence the decrease in luminosity of red giants.