Ch : Galaxies & the Expanding Universe How do astronomers know the universe is expanding? What is the big bang theory & what evidence supports it? How can dark matter be detected?

Galaxies:_____________________________ ____________________________________ _ Milky Way Stats LY across LY thick 5 Spiral Arms Our sun is 2/3 the way out on the Orion spiral arm. Moves around center at a speed of 500,000 mi/hr (It takes 200 million yrs to complete one rotation) Try this simulation: space.stsci.edu/resources/explorations/g alaxies-galore/build/index.html

Galaxies: Classified by Shape _______ Old stars; little nebula Young stars; lots of nebula Black holes & old stars in center; young stars in arms

Star Spectrums Also used to determine the _________________ ______________________ Expect to see lines for hydrogen …. But they aren’t in the right place?! Why?

Star Spectrums Spectroscopes collect visible light wavelength from stars. Each element has a unique pattern of lines when viewed. Spectrums tell us about a star’s________________

Doppler Effect RED SHIFT – a shift in absorption lines of star spectrum to the red wavelengths. Objects moving _____________have longer wavelengths (red) BLUE SHIFT Objects moving towards us have ____________ ____________________ Which spectrum is from a star/galaxy that is moving away from us? A B Listen to the Doppler Effect

Hubble’s Law = The farther a galaxy is away from us, the faster it is moving away from us The Universe is____________________! Evidence: The Doppler Effect (Wavelengths appear to change based on the motion of objects) If waves approach you … the waves bunch up on top of one another … or shorten (Blue Shift) If waves move away from you … the waves stretch out or get longer (Red Shift)

What does this spectrum tell you about the motion of the supercluster of galaxies?

Red Shifts What is going on here?

Red Shifted Spectrums Which galaxy is farthest from us? Which galaxy is moving away from us faster? 1 2 3

More distant galaxies= have ______________________ They are moving away from Earth with faster velocity than closer galaxies. The UNIVERSE IS EXPANDING! Hubble’s Law

Big Bang Theory The universe came into being at a single moment, in an event called ___________. All matter & energy of universe were concentrated into an incredibly hot, small, mass. An enormous ____________ sent matter and energy out into space. When: ________________yrs ago

Support for Big Bang 1.Red Shifts tell us Galaxies are ACCELERATING AWAY from a center (Expanding) 2. COSMIC Microwave BACKGROUND RADIATION Detected in 1965 Faint radiation coming from all directions Believed to be energy from Big Bang

What? Microwaves coming at us from everywhere, but no where specific. It’s lingering energy (echo) from Big BANG explosion! The Horn antenna in the Bell Telephone Laboratory discovered the universal microwave background radiation. Background Cosmic Microwave Radiation

Fate of Universe A.Expand forever / Galaxies drift apart? OR B. “Big Crunch” – Galaxies collapse into a center? Depends on how much mass there is in the universe … which is in dispute.

Dark Matter Dark Matter = Does not give off radiation & cannot be detected Exerts gravitational force on visible matter Universe may be 90% + dark matter Why do we think Dark Matter exists? Galaxies are accelerating faster than they should be (based on the observable matter in the Universe). The acceleration due to gravity does not match up with the amount of matter that we can see. This tells us that there must be more mass … we’re just not seeing it.

Ch 26.5 Questions 1.What theory states that the universe began as an explosion of an incredibly dense point of matter? 2.According to the theory of Big Bang, how old is our universe? 3.Our universe is currently … a. Contracting b. Expanding c. Staying the same 4. What does Hubble’s Law say about the motion of galaxies? 5. When scientists look at the spectrum for Andromeda, our neighboring galaxy, they notice that the lines are moved over to the blue end of the spectrum. Andromeda is … a.Moving towards us. b.Moving away from us. c.A constant distance from us. d.Not moving.

6.Quasars, are very distant galaxies. When scientists look at quasars with a spectroscope they would see the lines on their spectrum shifted to the (RED / BLUE) end of the spectrum. 7. How does the red – shift of far away galaxies support the big bang theory? 8.What kind of wavelength on the electromagnetic spectrum is lingering around like an echo from the Big Bang? 9.What are two possible scenarios for the future of the universe? 10.What is dark matter and how much of the universe do scientists think may be dark matter?