* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Linking Asteroids and Meteorites through Reflectance Spectroscopy
Survey
Document related concepts
Nuclear drip line wikipedia , lookup
Kerr metric wikipedia , lookup
Astrophysical X-ray source wikipedia , lookup
Hawking radiation wikipedia , lookup
First observation of gravitational waves wikipedia , lookup
Astronomical spectroscopy wikipedia , lookup
Planetary nebula wikipedia , lookup
White dwarf wikipedia , lookup
Nucleosynthesis wikipedia , lookup
Standard solar model wikipedia , lookup
Star formation wikipedia , lookup
Transcript
Conversations with the Earth Tom Burbine [email protected] Quiz on Thursday • Sun • Hertzsprung-Russell Diagram • Death of stars Main Sequence • Is not an evolutionary track – Stars do not evolve on it • Stars stop on the main sequence and spend most of their lives on it Sun ends it time on the main sequence • When the core hydrogen is depleted, nuclear fusion stops • The core pressure can no longer resist the crush of gravity • Core shrinks Why does the star expand? • The core is made of helium • The surrounding layers are made of hydrogen And .. • Gravity shrinks the inert helium core and surrounding shell of hydrogen • The shell of hydrogen becomes hot for fusion • This is called hydrogen-shell burning And … • The shell becomes so hot that its fusion rate is higher than the original core • This energy can not be transported fast enough to surface • Thermal pressure builds up and the star expands And .. • • • • More helium is being created Mass of core increases Increases its gravitational pull Increasing the density and pressure of this region When • When helium core reaches 100 million Kelvin, • Helium can fuse into a Carbon nucleus Helium Flash • The rising temperature in the core causes the helium fusion rate to rocket upward • Creates a lot of new energy However • The core expands • Which pushes the hydrogen-burning shell outwards • Lowering the hydrogen-burning shell’s temperature And • Less energy is produced • Star starts to contract Now • In the core, Helium can fuse to become Carbon (and some Oxygen) • Star contracts • Helium fusion occurs in a shell surrounding the carbon core • Hydrogen shell can fuse above the Helium shell • Inner regions become hotter • Star expands http://upload.wikimedia.org/wikipedia/commons/8/8d/Triple-Alpha_Process.png • Some carbon fuses with He to form Oxygen • 12C + 4He → 16O + gamma ray • Harder to fuse Oxygen with Helium to produce Neon Planetary Nebulae • There is a carbon core and outer layers are ejected into space • The core is still hot and that ionizes the expanding gas Planetary Nebulae White Dwarf • The remaining core becomes a white dwarf • White dwarfs are usually composed of carbon and oxygen • Oxygen-neon-magnesium white dwarfs can also form • Helium white dwarfs can also form High-Mass Stars • The importance of high-mass stars is that they make elements heavier than carbon • You need really hot temperatures which only occur with the weight of a very high-mass star Stages of High-Mass Star’s Life • Similar to low-mass star’s • Except a high-mass star can continue to fuse elements • When the fusion ceases, the star becomes a supernova • Supernova is a huge explosion Fusion • The temperatures of high-mass stars in its latestage of life can reach temperatures above 600 million Kelvin • Can fuse Carbon and heavier elements • Helium Capture can also occur where Helium can be fused into heavy elements “Deaths” of Stars • White Dwarfs • Neutron Stars • Black Holes White Dwarfs • White Dwarfs is the core left over when a star can no longer undergo fusion • Most white dwarfs are composed of carbon and oxygen • Very dense – Some have densities of 3 million grams per cubic centimeter – A teaspoon of a white dwarf would weigh as much as an elephant White Dwarfs • Some white dwarfs have the same mass as the Sun but slightly bigger than the Earth • 200,000 times as dense as the earth White Dwarfs • Collapsing due to gravity • The collapse is stopped by electron degeneracy pressure Electron Degeneracy Pressure • No two electrons can occupy the same quantum state The Sun • Will end up as a White Dwarf Neutron Star • • • • Neutron stars are usually 10 kilometers acroos But more massive than the Sun Made almost entirely of neutrons Electrons and protons have fused together How do you make a neutron star? • Remnant of a Supernova Supernova • A supernova is a stellar explosion. • Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months. Type Ia Supernova Type II Supernova This stops with Iron • Fusion of Iron with another element does not release energy • Fission of Iron does not release energy • So you keep on making Iron Initially • Gravity keeps on pulling the core together • The core keeps on shrinking • Electron degeneracy keeps the core together for awhile Then • The iron core becomes too massive and collapses • The iron core becomes neutrons when protons and electrons fuse together Density of neutron star • You could take everybody on Earth and cram them into a volume the size of sugar cube Explosion • The collapse of the core releases a huge amount of energy since the rest of the star collapses and then bounces off the neutron core • 1044-46 Joules • Annual energy generation of Sun is 1034 Joules How do we know there are neutron stars? • The identification of Pulsars • Pulsars give out pulses of radio waves at precise intervals Pulsars • Pulsars were found at the center of supernovae remnants Pulsars • Pulsars were interpreted as rotating neutron stars • Only neutron stars could rotate that fast • Strong magnetic fields can beam radiation out Black Holes • If a collapsing stellar core has a mass greater than 3 solar masses, • It becomes a black hole Black Hole • After a supernova if all the outer mass of the star is not blown off • The mass falls back on the neutron star • The gravity causes the neutron star to keep contracting Black Hole • A black hole is a region where nothing can escape, even light. Event Horizon • Event Horizon is the boundary between the inside and outside of the Black Hole • Within the Event Horizon, the escape velocity is greater than the speed of light • Nothing can escape once it enters the Event Horizon Black Hole Sizes • A Black Hole with the mass of the Earth would have a radius of 0.009 meters • A Black Hole with the mass of the Sun would have a radius of 3 kilometers http://www.astronomynotes.com/evolutn/remnants.gif Can you see a Black Hole? No • Black Holes do not emit any light • So you must see them indirectly • You need to see the effects of their gravity Evidence • The white area is the core of a Galaxy • Inside the core there is a brown spiralshaped disk. • It weighs a hundred thousand times as much as our Sun. http://helios.augustana.edu/~dr/img/ngc4261.jpg Evidence • Because it is rotating we can measure its radii and speed, and hence determine its mass. • This object is about as large as our solar system, but weighs 1,200,000,000 times as much as our sun. • Gravity is about one million times as strong as on the sun. • Almost certainly this object is a black hole. Any Questions?