Stars, Life and Light

S1-4-05b Identify the parts of the Sun and its source of energy. S1-4-06b Explain the basic life cycle of a star. KEY WORDS FusionCorePhotosphere ChromosphereCoronaRadiation zone Convection zone Main sequenceNebulaRed dwarf Neutron StarRed giantWhite dwarf SupernovaRed supergiantBlack hole Galaxy

Our Sun A small star About 5 billion years old (should last 5 more) Composed of 75% hydrogen and 25% helium All elements in plasma phase ( hotter state than gas) Energy comes from a Nuclear Fusion Reaction

Nuclear Fusion Reaction Fusion = join/merge Joining two hydrogen to create helium Releases large amount of energy

Fusion = joinFission = split Sun: joining (fusion) things to release energy Power Plants: splitting (fission) things to release energy

Layers of the Sun: Inside Core – centre (fusion takes place here) Middle – Radiation zone than convection zone Photosphere – cooler surface (5500 o C) sunspots, surface storms – the part we “see” Outside Chromosphere – inner atmosphere small solar explosions (flares), large (prominences) Corona – outer atmosphere (1 million o C) charged gas particles blow outward (solar winds)

Photosphere Core Chromosphere Radiation ZoneConvection Zone Corona

“Life Cycle” of a Star: Birth: Stars start out as Nebulae Nebula – huge cloud of dust and gases Youth – Middle Age: Gravity collapses a nebula into star that begins to release energy as a main sequence (MS) star Scientists categorize MS stars according to mass: Small - last longer (billions of years) Large - brighter but short-lived (few million yrs)

Actually nebulae captured by NASA space telescopes

Small MS star – Red Dwarf Very cool temperatures of their outer gases Death: Forms a cool, dim star called a White Dwarf Fades out until it no longer emits light energy We can’t see most Red Dwarf stars – their light is too weak

Medium MS star – like the Sun Separated into small-med and large-med Death: Runs out of elements for fusion reaction Collapses then swells to produce a Red Giant small-med eventually fades out as white dwarf large-med explodes as a Supernova leaving behind a Neutron star “Pulsar” neutron star

Large MS star Extreme energy produced for a short period Fuses heavier elements (iron) after lighter ones Death: Collapses then swells to a Red Supergiant Gravity collapses the largest into a Black Hole Stars are in balance: nuclear fusion explodes outwards, large gravitational force collapses inwards When the reactor runs out of elements to fuse, gravity wins and the star collapses and (sometimes) explodes

Nothing can escape the gravitational pull of a black hole

Nebulae main sequence (MS) star Red Dwarf White Dwarf Red Giant Supernova Neutron star Red Supergiant Black Hole Smallest Largest Medium Birth: Death: There is still more to this puzzle, but…this is close enough

Galaxies Huge collections of gas, dust and billions of stars and planets (collected by gravity) Constantly in motion Many shapes: spiral, elliptical, and irregular

Milky Way Galaxy Contains 400 billion stars Disc-shaped, with spiral arms – spiral galaxy We are on one of the arms Has a thicker Central Bulge Rotates around the bulge New evidence suggests the “central bulge” is actually a SUPER-MASSIVE BLACK HOLE!

CAN YOU ANSWER THESE QUESTIONS? S1-4-05b: How do stars like the Sun make energy? What are the parts of the Sun? S1-4-06b: How do stars form and how do small, med and large stars eventually “die?” KEY WORDS FusionCorePhotosphere ChromosphereCoronaRadiation zone Convection zone Main sequenceNebulaRed dwarf Neutron StarRed giantWhite dwarf SupernovaRed supergiantBlack hole Galaxy