Transcript powerpoint
The Star Cycle Birth • Stars begin in a DARK NEBULA (cloud of gas and dust)… aka the STELLAR NURSERY • The nebula begins to contract due to gravity in response to some interstellar disturbance • One or more PROTOSTARS are formed Birth • The protostar continues to collapse until its centre reaches a few million degrees K • Nuclear fusion begins. Hydrogen is converted to Helium. Brown Dwarf • Brown Dwarf - a protostar that does not have enough mass to reach the required temperature and pressure for nuclear fusion Main Sequence • Pressure, from energy released during fusion, balances gravitational contraction • Low mass stars take about 2 million years to reach main sequence • High mass stars only take 10, 000 years Main Sequence • Lowest mass main sequence stars are Red Dwarfs. Surface temp: 3000K • High mass main sequence stars are Blue Giants. Surface temp: 30,000K + Aging: Low Mass • When hydrogen in the core is all used up: – The core of helium collapses – The temp in the core increases – The area around the core expands • Becomes a Red Giant Aging: Low Mass • Eventually, the helium core ignites • Carbon and Oxygen are produced from “Helium burning” Aging: Low Mass • Late in the life of a Red Giant, oxygen and carbon can be “dredged up” by convection currents. • A star with enough carbon on its surface is called a Carbon Star Aging: Low Mass • If the mass is less than 8 solar masses, nuclear fusion stops with the production of Carbon and Oxygen • This is the fate of our Sun Death: Low Mass • Low mass stars eject their outer layers in the form of Planetary Nebula • The carbon and oxygen core is left behind as a White Dwarf Death: Low Mass • The White Dwarf is very hot and very small • Small white dwarfs are more massive than large white dwarfs Death: Low Mass • The White Dwarf eventually consumes the last of its fuel • Becomes a cold, dense, non-luminous Black Dwarf Aging: High Mass • If a star is greater than 8 solar masses, fusion does not stop with Helium burning • The carbon and oxygen core contracts and temp increases Aging: High Mass • Surface expands further. Becomes a Red Supergiant. • Surface as large as the orbit of Jupiter (1.5 billion km in diameter). • Core the size of Earth Aging: High Mass • Carbon and oxygen burning produce Neon, Magnesium, Silicon, and Sulphur • If it is massive enough, these will later form nickel, iron and other elements of similar atomic weight Aging: High Mass • When the core is full of iron, no more fusion is possible. Death: High Mass • Supernova – Core reaches a density of 4x1017 kg/m3. – Regions surrounding the core rush inward at unbelievable speeds – Increased pressure and temperature force the material back out – When shock waves reach the surface of the star, the outer layers explode Death: High Mass • Depending on the Mass, the supernova explosion will leave behind one of three things: • 1. White Dwarf – Glowing core similar to the remains of a low mass star. Its high mass will mean it is very small. Death: High Mass • 2. Neutron Star – Incredibly compact stellar corpse – Escape velocity is about half the speed of light – All protons and electrons are converted to neutrons Fast spinning neutron stars send out radio waves and are called PULSARS Death: High Mass • 3. Black Hole – The burned out core presses inward to create a density even greater than the neutron star – Escape velocity is greater than the speed of light – The gravity of the mass alters the fabric of spacetime Death: High Mass • 3. Black Hole – It forms a rapidly rotating disk around itself, called the ACCRETION DISK – X-rays are given off and matter is ejected in jets – Video: http://dsc.discovery.com/tvshows/other-shows/videos/how-theuniverse-works-birth-of-a-blackhole.htm