Part 2: Formation of the Universe STARS AND GALAXIES 1

What is the current theory of how the universe was formed that is accepted by most scientists? What evidence is there to support this theory? 2

Every object in the universe is moving, from electrons to galaxies. Scientists can calculate how fast galaxies are moving away from us or toward us using spectrographic measurements. Remember – a spectroscope separates visible light into the colors that make it up STARS ON THE MOVE Spectrograph of a Star 3

THE DOPPLER EFFECT The change in frequency of a wave for an observer moving relative to its source For sounds, this change in frequency is heard as a change in pitch. Approaching = wavelength shorter Moving away = wavelength longer 4

An effect similar to the Doppler effect is seen in light from stars in other galaxies. For almost all galaxies the shift is toward longer wavelengths, meaning the galaxies must be moving away from Earth. For visible light, red has the longest wavelengths, so the shift is toward the red end of the spectrum and is therefore called the red shift. RED SHIFT AND BLUE SHIFT 5

For a very few galaxies the shift is toward shorter wavelengths, meaning the star or galaxy must be moving toward Earth. For visible light, blue has short wavelengths, so the shift is toward the blue end of the spectrum and is therefore called the blue shift. The galaxy Andromeda exhibits a blue shift. RED SHIFT AND BLUE SHIFT 6

Most galaxies are moving away from us. In addition, scientists have found that the further a galaxy is from us, the faster it is moving away from us. Conclusion: The Universe is expanding. Analogy: Raisons in rising bread dough. This knowledge that the universe is expanding has led to the development of the Big Bang Theory. WHAT DOES RED SHIFT TELL US? 7

THE BIG BANG THEORY The Big Bang Theory is a theory for the origin and evolution of our universe. Remember: a theory is a logical explanation of events observed in nature. The Big Bang Theory says that 12 to 14 billion years ago*, the universe existed in a hot, dense, place that was only a few millimeters across and that it exploded and has since expanded, and continues to expand, into the vast and much cooler cosmos of today. *Most recent estimates by NASA put the age of the universe at about 13.7 ± 0.13 billion years! 8

THE BIG BANG THEORY The Big Bang Theory is a theory for the origin and evolution of our universe. Remnants of this hot dense matter can be measured as the now very cold cosmic microwave background radiation which still pervades the universe and is visible to microwave detectors as a uniform glow across the entire sky. *Most recent estimates by NASA put the age of the universe at about 13.7 ± 0.13 billion years! 9

Gravity is the force of attraction between objects. The more mass something has the great the force of gravity it exerts. After the Big Bang, the force of gravity began to pull matter together into clumps that would then become the stars, planets, and galaxies. Gravity is also why Andromeda is moving toward the Milky Way rather than away. THE ROLE OF GRAVITY 10

SO WHAT DO SCIENTISTS THINK WILL BE THE FUTURE OF THE UNIVERSE? In the universe, the momentum of expansion and the force of gravity oppose one another leading to two possibilities: Expansion wins and the universe keeps expanding forever and slowly cools (Open or Flat Universe); sometimes called the “Big Chill” or “Big Freeze” Gravity wins and collapses the universe (Closed Universe) – referred to as the “Big Crunch” – this could then lead to another “Big Bang” 11

An enormously bright object at the edge of our universe (12 billion light years away) which emits massive amounts of energy. In an optical telescope, they appear point-like, similar to stars. QUASAR 12 The X-ray image of the quasar PKS , about 10 billion light years from Earth, shows an enormous X-ray jet that extends at least a million light years from the quasar. Picture from the CHANDRA X-ray Observatory

First detected by looking at point sources of radio waves. Thus Quasar = quasi-stellar radio source Current theories hold that quasars are one type of active galaxy nucleus(AGN.) QUASAR 13 The X-ray image of the quasar PKS , about 10 billion light years from Earth, shows an enormous X-ray jet that extends at least a million light years from the quasar. Picture from the CHANDRA X-ray Observatory

Active Galaxy Nuclei (AGN): The centers of a class of galaxies which spew massive amounts of energy from their centers, far more than ordinary galaxies. Many astronomers believe supermassive black holes may lie at the center of these galaxies and power their explosive energy output. Include quasars, blazars, and Seyferts. ACTIVE GALAXIES 14