Star fact sheet
What stars are:
• Big balls of burning hydrogen
• Nuclear fusion reactions
• Very large (the sun, a medium sized star, is 1 million times the size of the earth)
What stars do:
• Create all types of atoms by fusing hydrogen atoms together.
• Spend most of their lives turning hydrogen into helium.
• Emit radiation such as heat, light and charged particles.
• Keep planets in orbit by their strong gravitational force
Life cycles of stars:
• All stars form from condensing clouds of mostly hydrogen gas in space called
nebulas.
• The nebula becomes hotter and denser as it attracts more and more material and
gains more and more gravity. This hot, dense cloud is called a proto star.
• When the heat and pressure from gravity reach a certain point, nuclear fusion
begins. When nuclear fusion begins the proto star becomes a star.
• The star will spend most of its life burning hydrogen into helium. This time is
called the Main Sequence.
• The end of a star’s life and how long that life is depends on its mass. The larger
star, the faster they burn fuel and the shorter their lives are.
• The star remains stable until it burns through its fuel and has lost too much mass.
• As the star loses mass by burning itself, it loses gravity allowing its outer layers to
move farther away from the core and the star expands to many times its original
size. For a small to medium-sized star we call this a red giant. Large to massive
stars will become red super giants.
• When all of the hydrogen is used up, the star no longer has the outward force
from the nuclear fusion reaction to hold out its outer edges and the star collapses
under its own gravity into an incredibly dense leftover core. This causes the outer
layers to be “puffed” of, leaving a cloud of gas and dust called a planetary nebula.
• Small to medium-sized stars will become white dwarf stars. They may begin
burning helium into the next heaviest element and repeat that process many times
with different elements. Eventually it no longer has the mass to continue nuclear
fusion and so it cools off and becomes a giant ball of whatever the last made element
was. This is called a black dwarf. No black dwarves exist because they take longer
to form than the universe has been in existence so far.
• Large and massive stars will do what the medium stars do, except they will keep
burning new elements until they start to make iron. At that point, the star dies
suddenly and its outer layers collapse in on the core with such force that it causes
the atoms to collapse into pure neutrons leaving an unimaginably dense core called
a neutron star. The collapsing material hits the surface so hard that it literally
bounces back billions of miles out into space in an explosion called a super nova.
The cloud of dust and gas left over is a nebula.
• Super massive stars will do what large and massive stars do, except instead of
exploding after they collapse, they just keep collapsing until there is no more matter,
just the gravity that is left over that is so strong that nothing can escape it, not even
light. We call this a black hole.