IPS Astronomy: Birth and Life of a Star

I. Nebulas All stars start out as a nebula All stars start out as a nebula A nebula is a stellar nursery A nebula is a stellar nursery A nebula is a large amount of gas and dust spread out in an immense (or big) volume A nebula is a large amount of gas and dust spread out in an immense (or big) volume Don’t get a star and a nebula confused. Don’t get a star and a nebula confused.

Nebula vs. Star Nebula Nebula –Large amount of gas in a large volume Star Star –Large amount of gas in a small volume Links: Links: –Jellyfish nebula Jellyfish nebulaJellyfish nebula –Eskimo nebula Eskimo nebulaEskimo nebula –Horse head nebula Horse head nebulaHorse head nebula

II. Protostar: in Greek, “proto” means earliest. Protostar = earliest star Gravity pulls gas and dust in (contracts) Gravity pulls gas and dust in (contracts) A contracting cloud is called a protostar. A contracting cloud is called a protostar. Pressure and temperature increase. Pressure and temperature increase. When the contracting gas and dust becomes so hot that nuclear fusion begins, a star is born!! When the contracting gas and dust becomes so hot that nuclear fusion begins, a star is born!! –Remember: nuclear fusion starts when hydrogen combines to form helium. During fusion, enormous amounts of energy are released. –Link: Pillars of Creation nebula Pillars of Creation nebulaPillars of Creation nebula

III. Main Sequence The star is fusing (burning) H into He (produces a lot of energy) The star is fusing (burning) H into He (produces a lot of energy) The star is now in the “prime of its life”; it is in equilibrium. The star is now in the “prime of its life”; it is in equilibrium. Over time; temp, luminosity, color change. Over time; temp, luminosity, color change. Our sun is in the main sequence phase Our sun is in the main sequence phase It will live for about 10 billion years It will live for about 10 billion years Our sun is now about 4.6 billion years old Our sun is now about 4.6 billion years old –Links: Planet swallower (artist) Planet swallower (artist) Planet swallower (artist) Planet swallower (artist) Sun Sun Sun Solar prominence Solar prominence Solar prominence Solar prominence

IV. Red Giant (or supergiant) Stars begin to die when they run out of fuel (hydrogen) Stars begin to die when they run out of fuel (hydrogen) The center of the star shrinks and the outer part expands The center of the star shrinks and the outer part expands The star may fuse all the elements through Fe The star may fuse all the elements through Fe Big, and bright, but low surface temp Big, and bright, but low surface temp All stars become a red giant or a supergiant All stars become a red giant or a supergiant –Camera Orion Camera OrionCamera Orion –Betelgeuse and Rigel Betelgeuse and RigelBetelgeuse and Rigel

V. Death Phases of a Star A dying star will take one of three paths extinction A dying star will take one of three paths extinction The mass of the star dictates which path it will take The mass of the star dictates which path it will take After the fuel is used up, a star will become a… After the fuel is used up, a star will become a… –White Dwarf, or –Neutron Star, or –Black Hole

Path #1: White Dwarfs White Dwarfs, small stars (1 X our Sun) White Dwarfs, small stars (1 X our Sun) The outer layers of the star grow bigger and slowly drift out into space. This material rejoins a nebula to be recycled into a new star The outer layers of the star grow bigger and slowly drift out into space. This material rejoins a nebula to be recycled into a new star The blue-white hot core is left and the “dead” star that is left behind is a white dwarf The blue-white hot core is left and the “dead” star that is left behind is a white dwarf The glow coming from the core is left-over energy from the old star. The core is NOT making any more energy. (Like turning off a light bulb) The glow coming from the core is left-over energy from the old star. The core is NOT making any more energy. (Like turning off a light bulb) Eventually, the energy glow is gone and the core is dark. It becomes a black dwarf. Eventually, the energy glow is gone and the core is dark. It becomes a black dwarf. –Links: Little Ghost Nebula, Helix Nebula, Eight-burst Nebula Little Ghost NebulaHelix NebulaEight-burst NebulaLittle Ghost NebulaHelix NebulaEight-burst Nebula

Path #2: Neutron Stars Neutron stars, medium stars (5 X our sun) Neutron stars, medium stars (5 X our sun) A supernova occurs when a supergiant star (5 X or more our sun) suddenly explodes A supernova occurs when a supergiant star (5 X or more our sun) suddenly explodes Some material rejoins a nebula Some material rejoins a nebula The remaining material from the star (or core) is a neutron star The remaining material from the star (or core) is a neutron star Neutron stars are even smaller and more dense than white dwarfs Neutron stars are even smaller and more dense than white dwarfs Some neutron stars spin, these are pulsars Some neutron stars spin, these are pulsars –Links: Cosmic Pearls supernova, Elusive Jellyfish nebula (neutron star), Tycho’s Supernova Remnant, A Dark Pulsar in CTA 1, Crab Pulsar Wind Nebula Cosmic Pearls supernova Elusive Jellyfish nebulaTycho’s Supernova RemnantA Dark Pulsar in CTA 1Crab Pulsar Wind NebulaCosmic Pearls supernova Elusive Jellyfish nebulaTycho’s Supernova RemnantA Dark Pulsar in CTA 1Crab Pulsar Wind Nebula

Path #3: Black Holes Black holes are the most massive stars (10-40 X our sun) Black holes are the most massive stars (10-40 X our sun) The (red) supergiant goes supernova, throwing the outer layers into space to rejoin a nebula The (red) supergiant goes supernova, throwing the outer layers into space to rejoin a nebula The gravity of the remaining core is so strong that the core collapses in on itself, creating an even stronger gravitational pull The gravity of the remaining core is so strong that the core collapses in on itself, creating an even stronger gravitational pull This gravity pulls everything to it This gravity pulls everything to it Nothing can escape its gravitational pull, not even light waves!! Nothing can escape its gravitational pull, not even light waves!! –Links: A view near a black hole, star ripped apart by BH, x-ray jet black hole, BH candidate Cygnus A view near a black holestar ripped apart by BH x-ray jet black holeBH candidate CygnusA view near a black holestar ripped apart by BH x-ray jet black holeBH candidate Cygnus

VI. Lifetimes of Stars How long a star lives depends on how much mass it has How long a star lives depends on how much mass it has Small mass stars live longer than large mass stars Small mass stars live longer than large mass stars –Stars that have more mass than the sun live a shorter lifetime. Approx. 10 million years –Stars that have less mass than the sun live longer. Approx. 200 billion years Example: A small car burns a gallon of gas more efficiently than a big SUV (exp 25/mpg vs 8/mpg) Example: A small car burns a gallon of gas more efficiently than a big SUV (exp 25/mpg vs 8/mpg) 07/es2807page01.cfm?chapter_no=visualization