The stars are formed by the dust and accumulation of gases present in the space. It typically formed by the fusion of the gases such as hydrogen, helium in the space. The pressure of the inner core of the star and the pressure exerted by the gases present outside the star influence the shape of the star. The celestial bodies of the universe like stars, planets and others are acted upon by the gravitational attraction. This is responsible for keeping all the gaseous molecules present in the star in shape.
He was 51 years old. He was 33 when he first started exploring. Then 17 years later he explored again so you add 17 +33 =50 . Then 11 years later he died so you add 11 to 50 =51