The Universe

Galaxies are believed to have formed from mergers of smaller galaxies and star clusters.

Galaxy Formationand Evolution

The separation between galaxies is usually not large compared to the size of the galaxies themselves, and galactic collisions are frequent.

The “cartwheel” galaxy on the left appears to be the result of a head-on collision with another galaxy, perhaps one of those on the right.

Galaxy Collisions

This galaxy collision has led to bursts of star formation in both galaxies; ultimately they will probably merge.

Galaxy Collisions

The Milky Way Galaxy also contains stars in its halo that appear to have been the result of the capture of smaller galaxies. The smaller galaxy dissolves within the larger one, a case of the littler one being “digested,” much as other dwarf companion galaxies were probably “consumed” by our Galaxy long ago.

Mergers of two spiral galaxies probably result in an elliptical galaxy; the merger of a spiral galaxy and a dwarf galaxy probably results in a larger spiral galaxy.

How big is big?The size of the Universehttp://htwins.net/scale2/

http://www.youtube.com/watch?v=HEheh1BH34Q&feature=relatedExtra credit: Make your own how big is big

video or game or demo!!!

Big Bang

According to the Big Bang model, the universe was originally in an extremely hot and dense state that expanded rapidly. As it expanded, it cooled and continues to expand today.

Big Bang Theory

• Occurred about 15 Billion years ago

• Started as a primordial atom- an infinitely small space

• Exploded in a a burst of energy

• Small super dense hot universe

• Over time it cooled and expanded away

If this expansion is extrapolated backward in time, all galaxies are seen to originate from a single point in an event called the Big Bang.

So, where was the Big Bang?

It was everywhere!

There is no center of the universe!!!

Wooooooo……

The Expanding Universe

You are the center of the Universe

http://www.youtube.com/watch?v=DsXsJtOQnTY

This can be demonstrated in two dimensions. Imagine a balloon with coins stuck to it. As we blow up the balloon, the coins all move farther and farther apart. There is, on the surface of the balloon, no “center” of expansion.

26.2 The Expanding Universe

Big Bang Model

• Follow the instructions on the lab sheet to model the expansion of the Universe

The same analogy can be used to explain the cosmological redshift

The Expanding Universe

If the universe is homogeneous, isotropic (the same in every direction), infinite, and unchanging, the entire sky should be as bright as the surface of the Sun. So why is it dark?

A contradiction known as Olber’s paradox

The Expanding Universe

Ober’s Paradox

http://www.youtube.com/watch?v=yQz0VgMNGPQ

http://www.youtube.com/watch?v=gxJ4M7tyLRE

Observation Inference

Almost all galaxies are red-shifted.

The most distant galaxies exhibit the greatest red-shift.

The ratio of recessional velocity to distance is between 50 and 100 km/s per kiloparsec and is called the Hubble Constant.

The Cosmic Background Explorer (COBE) found that the temperature of intergalactic space was not zero.

Observation Inference

Almost all galaxies are red-shifted.Almost all galaxies are moving away from the Milky Way.

The most distant galaxies exhibit the greatest red-shift.

The most distant galaxies are moving away the fastest.

The ratio of recessional velocity to distance is between 50 and 100 km/s per kiloparsec and is called the Hubble Constant.

The Universe has been expanding for 8 to 15 billion years.

The Cosmic Background Explorer (COBE) found that the temperature of intergalactic space was not zero.

The universe has not yet cooled from the rapid Big Bang expansion.

There are two possibilities for the Universe in the far future:

1. It could keep expanding forever.

2. It could collapse.

Assuming that the only relevant force is gravity, which way the Universe goes depends on its density.

The Fate of the Cosmos

If the density is low, the universe will expand forever. If it is high, the universe will ultimately collapse.

The Fate of the Cosmos

Dark Energy

Dark Energy vs. Dark Matter

While dark energy repels, dark matter attracts. And dark matter’s influence shows up even in individual galaxies, while dark energy acts only on the scale of the entire universe

Dark energy

The Universe is full of matter and gravity pulls all this matter together. The Hubble Space Telescope (HST) in 1998 observed a very distant supernovae showing that the Universe was actually expanding more slowly than it is today. Expansion of the universe is accelerating!

Roughly 68% of the Universe is dark energy, 27% is Dark matter. 5% is “normal “ matter

We do not have a good explanation of dark energy yet.

Dark Matter

http://science.nasa.gov/science-news/science-at-nasa/2013/14apr_ams/

Good resource for further information:http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/

Matter that influences the evolution of the universe gravitationally, but is not seen directly in our present observations. It neither emits or absorbs light.About one-quarter of the universe consists of dark matter, which releases no detectable energy, but which exerts a gravitational pull on all the visible matter in the universe.

The Milky Way is shaped like a disk that is about 100,000 light-years across. The stars in this disk all orbit the center of the galaxy. The laws of gravity say that the stars that are closest to the center of the galaxy — which is also its center of mass — should move faster than those out on the galaxy’s edge. Yet when astronomers measured stars all across the galaxy, they found that they all orbit the center of the galaxy at about the same speed. This suggests that something outside the galaxy’s disk is tugging at the stars: dark matter.

Dark Matter and the Milky Way

Calculations show that a vast "halo" of dark matter surrounds the Milky Way. The halo may be 10 times as massive as the bright disk, so it exerts a strong gravitational pull.

Video on Dark matter

http://www.youtube.com/watch?v=rLmcbjLVPKchttp://www.youtube.com/watch?v=fQLKS6BECdo