Part II:Stars and their EnvironmentDr Michael Burton

Stars and their Environment

Fundamental Properties of StarsParallax 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 SunColours give temperature.blue=hot, yellow=tepid (6000K), red=cool.

Stars and their Environment

Mass of the Sun2 x 1030 kilograms2 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 kgOr 2,000,000,000,000,000,000,000,000,000,000,000 kg!

Stars and their Environment

Hertzsprung-Russell DiagramFundamental tool for understanding stars.Graph of Luminosity (or magnitude) vs Temperature (or colour or spectral type).Main SequenceRed GiantsWhite DwarfsMass determines Main Sequence position.

Stars and their Environment

Nebulae Surrounding Star BirthStars form from collapse of Molecular Clouds under gravity (1106 1019 atoms 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

Star BirthProtostar - 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 12 brightest members.

Stars and their Environment

Extra-Solar Planetary SystemsOver 35 Planetary systems now detectedThrough wobble caused by orbit around starFind massive planets close to parent starNumerous Proto-planetary disks also found

An inevitable by-product of Star Formation?

Stars and their Environment

Stellar Evolution: Main Sequence LifeMain Sequence stars: gravity balances nuclear fusion,hydrogen to helium at 15 million K.More massive stars burn fuel more quicklyHave shorter lifetimes!Hydrogen shell burning when core all converted to helium. Leaves Main Sequence

Stars and their Environment

Stellar Evolution: Post Main SequenceStar ascends Giant Branchswells 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 shellDescends Horizontal Branch and contracts.Helium shell ignites, sheds outer layers.

Globular ClustersAncient star cities:Contain up to 107 stars, 1010 years old.Full range of stellar evolution displayedPosition on HR diagram determined by Mass.Turn-off point gives age.Horizontal Branch stars burning helium.

Stars and their Environment

Star Death: Low Mass StarsMain 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

Star Death: High Mass StarsMS Red Giant Supergiant Supernova Neutron Star or Black Hole.Nuclear fusion continues in shells to iron.Unstable, collapses in

Stellar RemnantsLow mass stars: White DwarfsHigh mass stars:supernova remnants, expanding at 10,000 km/smay 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

Black HolesGravity wins, even light cant 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!