Stars and Galaxies

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these superclusters have been mapped, and are grouped into long strings

300 million to a billion light-years long

100 to 300 million light-years wide

and only 10 to 30 million light-years thick

in between these strings are huge voids of galaxies, although some astronomers may have detected hot gas

Slide 75

Evolution of Galaxies

Slide 76

Origin of the Universe

Big Bang

Dominant scientific theory about the origin of the universe

Occurred ~13.7 billion years ago

What is the Big Bang?

How do we know?

Slide 77

What is the Big Bang?

Infinitely dense point not governed by our physical laws or time

All matter and energy contained in one point

Slide 78

Building a Universe

Instantaneous filling of space with all matter

Slide 79

History of the Universe

10-43 seconds - gravity separates from other forces

10-35 to 10-32 seconds - fundamental particles - quarks and electrons

10-6 seconds - quarks combine into protons and neutrons

1 second - electromagnetic and weak nuclear forces separate

3 minutes - protons and neutrons combine into atomic nuclei

105 years - electrons join nuclei to make atoms; light is emitted

105-109 years - matter collapses into clouds, making galaxies and stars

Orion Nebula - http://stardate.utexas.edu/resources/ssguide/planet_form.html

Slide 80

History of the Universe

Slide 81

Later History

Slide 82

Big Bang Theory

Image at http://map.gsfc.nasa.gov/universe/bb_theory.html

In 1915, Albert Einstein concluded that the universe could not be static based on his recently-discovered theory of relativity and added a "cosmological constant" to the theory of relativity because astronomers assured him that the universe was static

Aleksandr Friedmann and Abbe George LeMaitre are credited with developing the basics of the Big Bang model between 1922 and 1927; their calculations suggested that universe is expanding, not static.

Years later, Einstein called his cosmological constant the biggest mistake of his career

Slide 83

Expanding Universe

In 1929, Edwin Hubble showed that most galaxies are red-shifted (moving away from us), and that a galaxy’s velocity is proportional to its distance (galaxies that are twice as far from us move twice as fast)