insert: beyond our solar system
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Insert: Beyond our Solar System. Deployment of the Hubble Space Telescope in Earth orbit, April 24, 1990. The 300-meter radio telescope at Arecibo, Puerto Rico. Hertzsprung-Russell diagram. Shows the relation between stellar Brightness (absolute magnitude) and Temperature - PowerPoint PPT PresentationTRANSCRIPT
Insert: Beyond our Solar
System
Deployment of the Hubble Space Telescope in Earth orbit, April 24, 1990
The 300-meter radio telescope at Arecibo, Puerto Rico
Hertzsprung-Russell diagram Shows the relation between stellar
• Brightness (absolute magnitude) and• Temperature
Diagram is made by plotting (graphing) each star's • Luminosity (brightness) and• Temperature
Hertzsprung-Russell diagram
Parts of an H-R diagram • Main-sequence stars
• 90% of all stars• Band through the center of the H-R diagram• Sun is in the main-sequence
• Giants (or red giants) • Very luminous• Large• Very large giants are called supergiants• Only a few percent of all stars
Hertzsprung-Russell diagram Parts of an H-R diagram
• White dwarfs• Fainter than main-sequence stars• Small (approximate the size of Earth)• Lower-central area on the H-R diagram• Not all are white in color• Perhaps 10% of all stars
Hertzsprung-Russell diagram
The Orion Nebula is a well-known emission nebula
A faint blue reflection nebula in the Pleiades star cluster
Stellar evolution Two opposing forces in a star are
Gravity – contractsThermal nuclear energy – expands
StagesBirthMain-sequence stage
• 90% of a star's life is in the main-sequenceRed giant stageBurnout and death
• white dwarf, neutron star, or a black hole
Evolutionary stages
Stellar evolution
Stellar remnants White dwarf
• Small and Dense• Spoonful weighs several tons
Neutron star • Gravitational force collapses atoms
• Electrons combine with protons to produce neutrons• Pea size sample weighs 100 million tons• First one discovered in early 1970s Crab nebula
(remnant of an A.D. 1054 supernova)
Crab Nebula in the constellation Taurus
Stellar remnants Black hole
• More dense than a neutron star• Intense surface gravity lets no light escape• As matter is pulled into it
• Becomes very hot• Emits x-rays
• Likely candidate is Cygnus X-1, a strong x-ray source
Binary Pair with a Red Giant and a Black Hole
Galaxies Other galaxies
• Existence was first proposed in mid-1700s by Immanuel Kant
• Four basic types of galaxies • Spiral galaxy
• Arms extending from nucleus• About 30% of all galaxies• e.g., Milky Way
Face-on view of the Milk Way Galaxy
Edge-on view of the Milk Way Galaxy
Great Galaxy, a spiral galaxy, in the constellation Andromeda
Galaxies Other galaxies
• Four basic types of galaxies • Barred spiral galaxy • Elliptical galaxy • Irregular galaxy
The study of light Doppler effect
The apparent change in wavelength of radiation caused by the relative motions of the source and observerUsed to determine
• Direction of motion• Increasing distance – wavelength is longer
("stretches")• Decreasing distance – makes wavelength shorter
("compresses")
The Doppler effect
Red shifts Doppler effect
• Change in the wavelength of light emitted by an object due to its motion
• Movement away stretches the wavelength • Light appears redder
• Movement toward “squeezes” the wavelength• Light shifted toward the blue
• Expanding universe • Most galaxies exhibit a red Doppler shift
Raisin bread analogy of an expanding universe
Big Bang theory
Accounts for galaxies moving away from us
Universe was once confined to a "ball" that was • Supermassive• Dense• Hot
Big Bang theory Big Bang marks the inception of the
universe • Occurred about 15 billion years ago• All matter and space was created
Matter is moving outward Fate of the universe
• Two possibilities • Universe will last forever• Outward expansion sill stop and gravitational;
contraction will follow
Big Bang theory Fate of the universe
• Final fate depends on the average density of the universe
• If the density is more than the critical density, then the universe would contract
• Current estimates point to less then the critical density and predict an ever-expanding, or open, universe
End of Chapter 16