* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Giant Stars
Survey
Document related concepts
Nebular hypothesis wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Canis Minor wikipedia , lookup
History of Solar System formation and evolution hypotheses wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Chronology of the universe wikipedia , lookup
Stellar kinematics wikipedia , lookup
Stellar classification wikipedia , lookup
H II region wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Future of an expanding universe wikipedia , lookup
Star formation wikipedia , lookup
Transcript
Giant Stars irfu.cea.fr Energy Reserves • When stars reach the main sequence they are in equilibrium between gravity and radiation. Hydrogen-rich zones – Hydrogen to helium for 90% of lifetime – Too cool for helium fusion • Helium builds up in the core. Helium-rich core Red Giant • The helium in the core stops fusion except right along a hydrogen shell. Expanded hydrogen-rich zones • The helium core compresses to degenerate matter. – Density 1000 kg/cm3 • The hydrogen expands and cools to orange and red. Hydrogen-burning shell Helium core The Future Sun • The Sun will spend about 10 billion years on the main sequence. -20 -15 Abs. Magnitude -10 – Then expansion to red giant – Cool to class K or M -5 0 5 Sun 10 15 20 O B A F G K M Spectral Type • The Sun will expand to engulf at least Mercury and Venus. Stellar Evolution • Other mass stars will also run out of fuel and become giants. -20 -15 Abs. Magnitude -10 -5 10 M 3 M 0 5 0.5 M 10 0.02 M 15 20 O B A F G K M Spectral Type – Low mass stars expand a little – High mass stars grow more after less time Helium Fusion • Three helium nuclei can fuse into one carbon nucleus. – Temperature over 108 K (100 million) – High density to collide within 10-8 s photon photon helium-4 beryllium-8 carbon-12 Helium Flash • In a red giant, helium starts fusing and more energy is produced. – Mass over 2 M goes to slow helium burning – Mass from 0.5 M to 2 M, less stable equilibrium – Lasts a few hours • The rapid helium burning is called a helium flash. – Star slightly contracts after explosion – Horizontal branch of HR diagram Cluster Evolution • The M3 Globular cluster shows stars going giant. horizontal branch Asymptotic giant branch red giant branch main sequence – Main sequence – Red giant branch – Horizontal branch • The largest giants are on an asymptotic giant branch. – Degenerate carbon core