A low-mass star loses a significant fraction of its mass during its red-giant phase. Why do red giants lose mass? A red giant spins faster as it expands, causing gases at the surface to gain speed and escape. The surface gravity of a red giant decreases as the star expands, causing gases to escape from the surface. The supernova explosion that occurs when a red giant is formed expels the outer layers of the star. A red giant has a very high surface temperature, causing gases at the surface to gain energy and escape.