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Chapter 40 The Stars 40.1 Constellations • How many stars do you think the unaided eye can see? – Only about 3000 • Do stars look different through a telescope? – No, even with a telescope, stars are still just points of light • Why? – Because stars are so far away – Brightest are 10 to 1000 light-years away (1 light-year = 9.5 x 10^12 km= 9,500,000,000,000) – Pluto is 59.2 million (59,200,000) miles away Constellations • Early astronomers grouped stars into constellations • Constellations don’t move, but we move – Causes night sky to vary Can you identify the constellation? What star is this? 40.2 Birth of Stars • Interstellar dust spread out around space – Allows particles to condense to form star – Similar to cloud formation • Formation – Huge cloud of low-temp material – Gravity attracts other particles – Eventually have a protostar- a forming star more massive than the sun and bigger than our solar system Beyond a Protostar • Gravity causes ball to contract and increases temperature and pressure • At over 10 million Kelvins (18 million Fahreheit), hydrogen nuclei fuse to helium – Thermonuclear reaction – Releases tons of energy, stops contraction • Outward radiation and gas pressure = inward gravitational pressure = stable star Composition of Stars • Material in stars depends on how old they are – Older stars had only hydrogen and helium – Elements heavier than hydrogen and helium came from the core of stars – When stars die, they spew material out – Newer stars are composed of heavier elements – We are made of star dust! 40.3 Life and Evolution of Stars • Life span depends on how fast a star burns its fuel – Does a gallon of gas last longer in a truck or a car? – Similar in stars…smaller stars burn longer • Calculate mass of stars using binary stars – Binary stars revolve around each other – Observing them relative to each other gives us mass – Some think Sun might have a binary…Nemesis 40.4 Death of Stars • How are stars fueled? – Nuclear fuel – Fusion of hydrogen to helium • Average mass stars like our Sun – Contract and raise temperature – Ignites the hydrogen and helium to produce a red giant – Our sun will reach that stage in 5 billion years Death of Stars • Stars smaller than the sun – – – – No source of nuclear energy so they shrink Shrink and form expanding shells These form planetary nebula Core is white hot….a white dwarf Fades into a black dwarf If it has a binary, pulls hydrogen from there and creates a nova The Ant Nebula, a cloud of dust and gas whose technical name is Mz3, resembles an ant when observed using ground-based telescopes. The nebula lies within our galaxy between 3,000 and 6,000 light years from Earth. In third place is Nebula NGC 2392, called Eskimo because it looks like a face surrounded by a furry hood. The hood is, in fact, a ring of comet-shaped objects flying away from a dying star. Eskimo is 5,000 light years from Earth. Starry Night, so named because it reminded astronomers of the Van Gogh painting. It is a halo of light around a star in the Milky Way. In sixth place is the C one Nebula. The part pictured here is 2.5 light years in length (the equivalent of 23 million return trips to the Moon). 40.5 Supernova • Star life cycle depends on its mass • Larger Stars produce more heat – Don’t become white dwarfs – Fusion occurs until Iron is formed – Eventually starts to collapse Final Collapse • Collapse, explosion, and remnant timeline? • Explosion creates heavier elements like gold, silver, and lead • Called a supernova • Supernova so bright, they can even be seen by day Neutron Stars • Inner part of supernova implodes – Compressed the core – Creates neutron star • Neutron stars: – Spin at great speeds – Create pulsars – low-frequency radio emissions 40.6 Black Hole • Largest stars have no force strong enough to stop them from contracting • Collapse until they disappear from observable universe…a black hole • Speed of collapse increases until it is faster than the speed of light, therefore we can’t see anything! 40.7 Galaxies • Galaxy = large group of stars, planetary nebulae, and interstellar dust • How many stars do you think make up the Milky Way Galaxy? – 200 billion – Seen as a faint band of light across the sky • Most striking feature of Milky Way is spiral arms = hot, blue stars, and clusters of young stars Elliptical Galaxies • Most common • Dim, so most difficult to see • Have little gas and dust, so cannot create new stars Irregular Galaxies • Small and faint • Large clouds of gas and dust Spiral Galaxies • Most beautiful • Lots of newly formed stars • 2/3 of all KNOWN galaxies – Only 15 to 20% of all galaxies – Elliptical more common, just harder to see