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Part II: Stars and their Environment

Part II: Stars and their Environment. Dr Michael Burton. Fundamental Properties of Stars. Parallax gives distance to closest stars. Measured in Light Years . Luminosity from 0.001 -100,000 x Sun. Masses from binary star orbits (K3 rd L). 0.01 to 100 x Sun Colours give temperature.

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Part II: Stars and their Environment

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  1. Part II:Stars and their Environment Dr Michael Burton Stars and their Environment

  2. Fundamental Properties of Stars • Parallax gives distance to closest stars. • Measured in Light Years. • Luminosity from 0.001 -100,000 x Sun. • Masses from binary star orbits (K3rdL). • 0.01 to 100 x Sun • Colours give temperature. • blue=hot, yellow=tepid (6000K), red=cool. Stars and their Environment

  3. Mass of the Sun • 2 x 1030 kilograms • 2 million, million, million, million, million kg • 2,000,000,000,000,000,000,000,000,000,000 kg • But not 2,000,000,000,000,000,000,000,000,000 kg • Or 2,000,000,000,000,000,000,000,000,000,000,000 kg! Stars and their Environment

  4. Hertzsprung-Russell Diagram • Fundamental tool for understanding stars. • Graph of Luminosity (or magnitude) vs Temperature (or colour or spectral type). • Main Sequence • Red Giants • White Dwarfs • Mass determines Main Sequence position. Stars and their Environment

  5. Nebulae Surrounding Star Birth • Stars form from collapse of Molecular Clouds under gravity (1106 1019atoms per cc) • Dark Nebulae (100 K). • Absorb light through extinction. • Shine through fluorescing hydrogen gas. • Red Nebulae (HII regions) (10,000K). • Reflect starlight by dust scattering. • Blue Nebulae (cf daytime sky). Stars and their Environment

  6. Star Birth • Protostar - collapsing core of molecular cloud. Pressure builds till heat ignites nuclear fusion in centre, becoming a star. • Associated with disks ( planetary systems), outflows and jets. • Disperse their cocoon to become visible. • Typically form in clusters, dominated by light from 1–2 brightest members. Stars and their Environment

  7. Extra-Solar Planetary Systems • Over 35 Planetary systems now detected • Through wobble caused by orbit around star • Find massive planets close to parent star • Numerous Proto-planetary disks also found An inevitable by-product of Star Formation? Stars and their Environment

  8. Stellar Evolution: Main Sequence Life • Main Sequence stars: • gravity balances nuclear fusion, • hydrogen to helium at 15 million K. • More massive stars burn fuel more quickly • Have shorter lifetimes! • Hydrogen shell burning when core all converted to helium. • Leaves Main Sequence Stars and their Environment

  9. Stellar Evolution: Post Main Sequence • Star ascends Giant Branch • swells to a cool, extended Red Giant. • 3000K, Radius ~ 1 AU. • Helium Flash: when fusion of helium begins in core (at ~100 million K): • Helium burning core + • Hydrogen burning shell • Descends Horizontal Branch and contracts. • Helium shell ignites, sheds outer layers.

  10. Globular Clusters • Ancient star cities: • Contain up to 107 stars, 1010 years old. • Full range of stellar evolution displayed • Position on HR diagram determined by Mass. • Turn-off point gives age. • Horizontal Branch stars burning helium. Stars and their Environment

  11. Star Death: Low Mass Stars • Main Sequence  Red Giant  Planetary Nebula + White Dwarf. • Planetary Nebula: ejected envelope, • forms expanding shell. • White Dwarf: burnt-out stellar core. • Mass of star but size of Earth. • Teaspoon weighs 5 tons! Stars and their Environment

  12. Star Death: High Mass Stars • MS  Red Giant  Supergiant  Supernova  Neutron Star or Black Hole. • Nuclear fusion continues in shells to iron. • Unstable, collapses in <1s. Bounce off rigid core detonates star – Supernova! • Shines as bright as a galaxy for a few days! We are Stardust from Supernovae! Stars and their Environment

  13. Stellar Remnants • Low mass stars: White Dwarfs • High mass stars: • supernova remnants, expanding at 10,000 km/s • may trigger future star formation? • Neutron stars: mass star but just 10 km across. • Teaspoon weighs 100 million tons! • Seen as Pulsars, flashing beacons in space. • or Black Holes? Stars and their Environment

  14. Black Holes • Gravity wins, even light can’t escape! • Collapse to a ‘Singularity’ with an ‘Event Horizon’ (R = 2GM/c2). • Mass, angular momentum and charge only. • Cosmic censorship, time slows down. • Supermassive Black Holes in galaxy cores. • Primordial Black Holes in Big Bang. • Black Holes evaporate through production of virtual particles at event horizon!

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