Up Studying Stars Star Layers Magnitude The Dippers Closest Stars Star Colors Star Life Temperature HOME    Stars are energetic balls, made mostly of hydrogen, that burn gas.  Most stars are made of two gases -  hydrogen and helium.  Stars are born in a nebula.  A nebula is a huge cloud of dust and gas.  When a star is born, particles in the nebula attract each other.   The gravitational pull of these particles attracts more particles, and it begins to make pressure.   Gravity pulls the rest together, and the energy that causes, makes the star heat up and glow.  A star is born!  When a star runs out of gas, it will swell up into a red giant, and stay like that for awhile.  Then, the outer surface will break away, and only a tiny, very dense, white dwarf star will remain.  When that dies, a tinier, even denser, black dwarf star will remain.  

    It was the 20th century before astronomers finally figured out how a star is born, how it lives and how it dies.  The life cycle of a star is quite complex.  A smaller star’s life cycle starts as a nebula.  At this stage, the star is not a star yet.  It is just a lot of hot gas and dust floating around in space.  The nebula, after gathering much gas, develops into a Protostar.  At this point, it is a star, though it has not begun to shine yet.  After that, it is either a blue, white or yellow star.  Then it changes into a red giant.  This star is now at its largest size (the size varies from only a 100,000 miles across, up to 1,000 times the diameter of our Sun, which is about 9 billion miles).  It then begins to lose heat.  Then it becomes a planetary nebula (a dying star), with a white dwarf (the collapsed core of the star).  After that, it changes into a dark, black dwarf (a dead, cold star with no heat).  Our Sun may live to be 4.5 billion years old.  A star is born, lives for a couple million years, blows up in a giant nova, and then burns out (dies).  A nova is a massive star explosion.  Did you know that dimmer, less “attractive” stars live much longer than big, bright and “flashy” stars?  It is because they do not use up as much gas.