1 / 14

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.

zahur
Download Presentation

Part II: Stars and their Environment

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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!

More Related