Science 9

 Gravity is a force that pulls objects toward each other  The more mass an object has, the more gravity it exerts  The Sun has stronger gravity than Earth  The force gets smaller as the distance between two objects increases

 All stars begin as nebulas  Huge clouds of gas and dust, composed mainly of hydrogen and helium  Matter forms into clumps due to gravity  Clumps combine and pack closely together  Nuclear fusion begins  This is the beginning of a star’s “life”

 When a star nears the end of its life, it runs out of hydrogen and other fuels needed to produce energy  Pressure decreases in the star so the star swells (gets bigger) and cools down (turns red)  Stars equal to or smaller than the sun become red giants  Stars much larger than the Sun become red supergiants

 Smaller stars die when nuclear reactions decrease, the core shrinks and parts of the star float away  White dwarfs are small stars with a higher temperature than red or yellow stars

 An enormous explosion that occurs at the end of a large star’s life  The core collapses inward to become either a neutron star or a black hole  They are rare events

 When extremely large stars die, the resulting core is called a neutron star  An extremely dense star made of neutrons  A pulsar is a type of neutron star that emits light and radio waves – the light appears as pulses

 When a star at least 30x’s the size of the Sun dies, the result is a black hole  The core’s force is so strong, nothing can escape, not even light  They can exist undetected  The x-rays of a black hole can be detected and other objects orbiting it  It is composed of matter only a few kilometres across – should be called dark body

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