If Same Size as our Sun

• If the star is the same size as our sun, then at some stage, the hydrogen in the star begins to run out. At this point, the outward force due to fusion energy is less than the inward force due to gravity. This causes the star to collapse inwards. The collapse of the star causes its temperature to increase. Now helium nuclei fuse together to create heavier elements.
• The star expands to form a red giant. At some point, the red giant stops fusing helium. At this stage, the star shrinks & forms a white dwarf. Because the white dwarf is no longer carrying out fusion, it gradually cools down. Eventually it stops releasing any energy and it forms a black dwarf.