Life and Death of Stars All stars form inside a nebula as the gas contracts because of gravity. The Orion Nebula, an area of active star formation Forming a protostar The area with the greatest amount of matter will draw material towards it through gravity The area with the greatest amount of matter will draw material towards it through gravity This ball begins to spin, build up pressure, and heat up This ball begins to spin, build up pressure, and heat up Eventually the temperature of the spinning protostar rises to millions of degrees Celsius which is hot enough for nuclear fusion reactions to start. Eventually the temperature of the spinning protostar rises to millions of degrees Celsius which is hot enough for nuclear fusion reactions to start. This process combines two hydrogen atoms into one helium atom giving off a lot of heat and light. This process combines two hydrogen atoms into one helium atom giving off a lot of heat and light. Protostars A protostar is generally invisible to telelscopes and must be viewed using infrared A protostar is generally invisible to telelscopes and must be viewed using infrared Protostars eject large amounts of material in the form of bipolar jets. Protostars eject large amounts of material in the form of bipolar jets. A Star is Born! Energy from the core reaches the stars outer perimeter and the star switches on and begins to shine. Energy from the core reaches the stars outer perimeter and the star switches on and begins to shine. Lifecycle of stars: depends on their initial mass Low Mass Stars Burn slowly and last for 100 billion years. Burn slowly and last for 100 billion years. They shine weakly as red dwarfs. They shine weakly as red dwarfs. As they run out of fuel they collapse under their own gravity. As they run out of fuel they collapse under their own gravity. Red dwarfs cool to become white dwarfs and eventually black dwarfs. Red dwarfs cool to become white dwarfs and eventually black dwarfs. Medium Mass Stars Our star is a normal sized star Our star is a normal sized star Big stars are called Giants and Supergiants Big stars are called Giants and Supergiants Medium Mass Stars Burn their fuel faster (about 10 billion years) Burn their fuel faster (about 10 billion years) They burn out, re-ignite and then eventually collapse and burn out again. They burn out, re-ignite and then eventually collapse and burn out again. Once a stars core reaches lead it cannot support fusion any longer and it collapses. Once a stars core reaches lead it cannot support fusion any longer and it collapses. High Mass Stars More than 10X the mass of the Sun More than 10X the mass of the Sun Burn all of their fuel in less than about 7 billion years Burn all of their fuel in less than about 7 billion years Goes through many cycles of collapse and expansion causing fusion to form new elements such as iron at the core Goes through many cycles of collapse and expansion causing fusion to form new elements such as iron at the core Final collapse causes an explosion or a Supernova Final collapse causes an explosion or a Supernova This causes elements to fuse in various combinations and all the elements in the periodic table are formed this way. This causes elements to fuse in various combinations and all the elements in the periodic table are formed this way. After the Supernova If the star was 1.5 3 times the size of the sun it forms a neutron star If the star was 1.5 3 times the size of the sun it forms a neutron star The star is so heavy that it cant support its own weight so the atoms collapse creating a ball of neutrons. The star is so heavy that it cant support its own weight so the atoms collapse creating a ball of neutrons. We see neutron stars from the radiation that shoots out either end. Only a few kilometers in size. After the Supernova If the star was over 40X times the mass of the Sun, the star is so heavy that not even the neutrons stay apart and it collapses forming a black hole. If the star was over 40X times the mass of the Sun, the star is so heavy that not even the neutrons stay apart and it collapses forming a black hole. Black holes are so dense that not even light can escape it. Black holes are so dense that not even light can escape it. We find black holes by looking for objects in space that orbit seemingly empty space. Constellations This is a group of stars that from Earth resemble a recognizable form. This is a group of stars that from Earth resemble a recognizable form. There are 88 constellations in total. There are 88 constellations in total. These recognizable patterns of stars have names derived from ancient legends These recognizable patterns of stars have names derived from ancient legends Constellations can be used to determine direction. You can easily recognize the big dipper You can easily recognize the big dipper The two outside stars of the bowl point towards Polaris in the handle of the little dipper The two outside stars of the bowl point towards Polaris in the handle of the little dipper If you are facing Polaris you are facing north. If you are facing Polaris you are facing north. You can use the big dipper to point out other stars The big dipper can be used to point out the North star of the little dipper. The big dipper can be used to point out the North star of the little dipper. Imagine that it slams its bowl onto the head of Leo Imagine that it slams its bowl onto the head of Leo Follow the arc to Arcuturus in Bootes and speed on to Spica in Virgo Follow the arc to Arcuturus in Bootes and speed on to Spica in Virgo Why different constellations are visible at different times of the year. On the autumnal equinox each year, the Sun is in the constellation Virgo. On the autumnal equinox each year, the Sun is in the constellation Virgo. This means that we see only the stars on the other half of the sky centered around Pisces This means that we see only the stars on the other half of the sky centered around Pisces The opposite is true in the spring. The opposite is true in the spring. Different constellations at different times of the year The summer triangle