STARS Amole Spectra of Science 2013 What are

STARS Amole Spectra of Science 2013

What are Stars?

What are Stars? • A large celestial body of hot gas that emits light • Greeks grouped stars in patterns called constellations • Use the unit light-year to measure distances between stars – 9. 5 x 1015 m • Driven by nuclear fusion reactions

Why do Stars look Different from One Another? • • Size Distance from Earth Temperature Stage of Life Cycle

Characteristics of Stars • Color indicates temperature – Blue (Short λ) = Hot – Red (Long λ) = Cool – The hotter they are the faster they burn out • Magnitude – Brightness – Smaller numbers represent brightest stars

Classification of Stars • Classified by temperature and brightness • Decreasing Temperature and brightness • • Oh, Be A Fine Girl, Kiss Me

Classification of Stars Class Temperature Color O 20, 000 - 60, 000 K Blue B 10, 000 – 30, 000 K Blue-white A 7, 500 – 10, 000 K White F 6, 000 – 7, 500 K Yellow-white G 5, 000 – 6, 000 K Yellow K 3, 500 – 5, 000 K Orange M 2, 000 – 3, 500 K Red

H-R Diagram

Nuclear Fusion • Strong gravitational forces hold stars together • Energy from fusion creates outward pressure balancing inward pull • Hydrogen atoms are fused to form helium

Layers of Stars • Energy moves through layers by radiation and convection • May take millions of years for energy to work its way through star to surface • After leaving the surface it enters space traveling at the speed of light, 3 x 108 m/s

Temperatures of the Sun

What Happens When a Star Runs out of H? • Begins to fuse He • Then, a succession of heavier elements • Iron is the most stable; it requires energy verses creating it • Star begins to die

Life Cycle of Stars

Stellar Nebula • Nebulas are clouds of dust and gas from which stars are born – Grains of carbon and silicon • Matter compresses due to own gravity • Temperature and pressure slowly increase from compaction Omega Nebula

Eagle Nebula

Lagoon Nebula

Bubble Nebula

Crescent Nebula

Orion Nebula

Crab Nebula

Adult Star • Actively undergoing hydrogen fusion • Main Sequence star • Spends most of its lifetime in this phase • 90% of stars in the galaxy are in this phase • An average size like our sun will “burn” much longer than a larger, more massive star

Red Giants and Supergiants • When a star runs out of hydrogen, it begins to die • Energy from fusion no longer counteracts gravity, and the core collapses • Causes outer layers to expand • Average stars create Red Giants • Massive stars create Red Supergiants

Average Size Star Stellar Nebula Adult Red Giant and then….

Planetary Nebula. White and Black Dwarfs • Core runs out of He, and is no longer able to fuse the remaining heavier elements • The star blows its outer layer away • The core remains behind and burns hot • Eventually cooling Little Ghost Nebula

Stingray Nebula

Ring Nebula

White and Black Dwarfs • After the star blows its outer layer away • The core remains behind and burns hot for a while – Called a white dwarf • Eventually it may cool and emit little to no light – becomes a black dwarf

Massive Size Star Stellar Nebula Adult Red Super Giant and then….

Supernova • Massive stars end in violent explosions that blow away the outer layers of the star • These stars result in either a neutron star or supernova

Neutron Star • Leftover core has between 1. 4 – 3 solar masses • Collapses so much that protons and electrons combine to form neutrons • Very dense (a thimbleful weights more than 100 million tons) • Emit radio waves (pulsars)

Black hole • Leftover core collapses into tiny space • So much that not even light can escape its gravity • Star’s act different around blackholes – (high frequency light –xrays) • Less than 1% of material near even horizon actually enters blackhole – Due to angular momentum (they orbit instead)

Milky Way Black Hole

Life Cycle of Stars

Life Cycle of Stars

Black Holes

Death of a Star Simulations