BEYOND OUR SOLAR SYSTEM CHAPTER 25 Part II

INTERSTELLAR MATTER NEBULA BRIGHT NEBULAE EMISSION NEBULA REFLECTION NEBULA SUPERNOVA REMANTS DARK NEBULAE

BRIGHT NEBULA EMISSION NEBULA –Consists of hydrogen –Absorbs UV radiation –Fluorescence - reradiate (emit) energy as visible light Cocoon Nebula

BRIGHT NEBULA (cont.) REFLECTION NEBULA –Composed of interstellar dust –Reflects light from nearby stars M-78

BRIGHT NEBULA (cont.) SUPERNOVA REMNANT –Remains of an exploded star Crab Nebula

DARK NEBULA Dark Nebula region  No close stars for it to emit or reflect light  “Holes in the Heavens” – starless region

STELLAR EVOLUTION STAR BIRTH  Nebula – interstellar clouds of gas & dust  Gravity – cloud begins to contract  BARNARD OBJECTS – are cold, dark Nebulae –Star forming clouds 92% hydrogen, 7% helium, <1% heavier elements Gravity – cloud begins to contract  Triggering Star formation –shockwave from nearby star that goes ‘Supernova’ –Previously formed stars in the nebula

STELLAR EVOLUTION STAR BIRTH Giant molecular cloud begins to collapse slowly Protostar will form - Nuclear fusion has not begun yet Matter begins to collapse into dense clumps More than one star may form Thermo-nuclear fusion begins in the core. Stars begin to shine

 forms when nebula cloud contracts due to gravity - Fragments form lumps that grow - bigger the lumps - the stronger the force of gravity - until Core reaches the “critical temperature” of 10 million K - nuclear fusion begins PROTOSTAR

PROTOSTAR (cont.) ORION NEBULA VISIBLE LIGHT INFRARED SPECTRUM PROTOSTAR

A STAR IS BORN The Sun – Our Star An Average Star (Main sequence)  Core reaches “critical temperature” of 10 million K, nuclear fusion begins

STELLAR EVOLUTION Fusion gas pressure : –trying to expand and blow star apart Gravity : –trying to contract & hold star’s mass together MAIN-SEQUENCE STAGE  Star establishes an equilibrium

STELLAR EVOLUTION MAIN-SEQUENCE STARS Fusion of hydrogen into helium –Hydrogen-burning at the core –stars spends 90% of their life in main-sequence stage –Stars age at different rates Large mass stars have short life spans Small mass stars have long life spans –Our Sun – 10 billion yr. Life-span

STELLAR EVOLUTION RED GIANT STAR STAGE –Hydrogen burning in core ends –Gravity & gas pressure become unbalanced Core contracts & outer shell expands –Surface cools & appears red Core continues to contract & temperature rises –100 million K –“Helium” Burning occurs Fusion process creates C carbon –Further fusion can produce heavier elements up to Fe iron

LIFE CYCE OF A SUNLIKE STAR

THE FUTURE OF STARS DEPENDS ON INITIAL MASS

STELLAR EVOLUTION BURNOUT & DEATH DEATH OF LOW-MASS STARS –½ the mass of our Sun –Collapse into a White Dwarf

STELLAR EVOLUTION BURNOUT & DEATH  DEATH OF MEDIUM-MASS STARS –Sun-like stars between ½ to 3x Sun’s mass –Planetary Nebula – outer shell cast off and ring of gas forms –Core collapses into White Dwarf

STELLAR EVOLUTION BURNOUT & DEATH Supernova –Core contracts –Pressure causes core to explode DEATH OF MASSIVE STARS

H-R Diagrams & Stellar Evolution  Illustrates changes in the life-span of stars  Stars do not physically move  Position represents color & absolute magnitude at various stages of star evolution

Nucleosyntheis Process that creates new elements inside stars Mass of star determines highest atomic # of element it can produce –Elements up to iron (Fe) produced during fusion –Rare heavier elements form during Supernova event

STELLAR REMNANTS Stars collapse into one of three states –After fuel consumed White dwarf Neutron star Black hole All composed of extremely dense material & extreme surface gravity

WHITE DWARF Remains of medium & low mass stars –Size of Earth –Mass = the sun –Spoonful of matter = several tons The Sun began as a nebula, will spend much of its life as a main-sequence star, and then will become a red giant, planetary nebula, white dwarf, and finally a black dwarf.

BLACK DWARF  As white dwarf cools down it no longer emit heat or light  time required to reach this point is longer than the current age of the universe of 13.7 billion years  black dwarfs aren’t expected to exist in the universe yet  temperature of the coolest white dwarfs is a way of determining the age of the universe

NEUTRON STAR OR BLACK HOLE

SUPERNOVA Only natural event in universe energetic enough to spark fusion that can create the heavier elements Elements created are heavier than Iron (Fe)

STELLAR EVOLUTION BURNOUT & DEATH DEATH OF MASSIVE STARS NEUTRON STAR –Core collapses to about 20 km in diameter Form from stars x that of Sun Diameter is about 3-20 km Made up entirely of neutrons –density – 1 tsp = 100 million tons

PULSAR Neutron star that rapidly rotates –emits intense short bursts of radio waves Rotations rates: –between 33 milliseconds and 3.75 seconds

STELLAR EVOLUTION BURNOUT & DEATH DEATH OF MASSIVE STARS Black Hole –A Super-massive star’s core so dense that the gravity prevents even light from escaping

BLACK HOLE Core mass > 3x that of Sun core collapses, matter is so massive that its gravity prevents light from escaping Evidence that they exist –X-rays are emitted –Objects are seen orbiting seemingly empty spaces –Light bends around seemingly empty space

SUMMARIZING A STAR’S EVOLUTION The stars “Evolutionary Path” is set Depends on the Stars mass: Massive Stars –Live fast and die violently, using up their hydrogen much faster due to high energy output Less Massive Stars –Live long and die quietly

GALAXIES