The life and death of stars Stars take millions of years to form. They then go through a stable period in their life and finally they die. Sometimes in spectacular fashion

How are stars formed? After the Big Bang matter was thrown throughout the Universe. This matter consisted mainly of hydrogen gas. In areas where there was a lot of hydrogen, it was pulled together slowly over millions of years to form a star. Q.What caused the hydrogen to be pulled together? A.The force of gravity Eventually, the molecules of hydrogen were pulled so close together that they started to get extremely hot. Q. What happened next? A. The hydrogen molecules start to fuse (join together) to make helium. This process is called nuclear fusion.

The stable period in a star’s life The hydrogen in a star is pulled together by its own force of gravity. Q. But why doesn’t the star just collapse under it’s own force of gravity? A. There must be another force that balances this force of gravity. This force is provided by the nuclear fusion taking place in the star. Vast amounts of energy are released that create the pressure that balances the force of gravity.

The stable period in a star’s life There are two forces acting on a star. Force of __________ Pressure due to nuclear _______ During the stable period of a star’s life these two forces are _________. This means that they are equal in ____ but act in opposite __________. Our Sun is about half way through its stable period. Scientists believe that it will remain stable for about 4500 million years.

The Death of Stars During the stable period of a star’s life hydrogen fuses to form helium. Q. What do you think causes the end of this stable period? A. Most of the hydrogen is used up. Mostly helium remains. Q. What effect will this have on the outward pressure? A. It will decrease and the star will collapse under its own gravity. The helium atoms will then get closer together and start to fuse. Heavier elements will be formed and vast amounts of energy will be released. Q. What do you think will happen to the outward pressure and the star? A. The pressure will increase and the star will expand to something called a RED GIANT.

The Death of Stars Red Giant When all the ___________ gas is used up, the star initially ___________ under its own force of gravity. Helium gas then _______ to form heavier ___________ and the star ___________ to form a RED GIANT.

What happens next? What happens after the red giant stage depends on the mass of the star. For stars up to 3 times the mass of the Sun White dwarf, gradually cools to a brown dwarf Stars with a mass greater than 3 times that of the Sun A SUPERNOVA explosion occurs. Dust, gases and heavy elements are thrown into space. Neutron star. It’s density is millions of times greater than a white dwarf.

And finally……..Black holes and second generation stars. Black holes Really massive stars will collapse to form black holes after the supernova stage. They are called black holes because light cannot escape them. Second generation stars Second generation stars are stars that have formed from the remains of a supernova. Unlike first generation stars, they contain heavier elements like lead, silver and gold.