Astronomy Lesson - 20th Apr 2010
Venue: LT@SRC
Time: 1530 - 1730 h
Conducted by Lim JN.

Learning outcomes
At the end of the lesson, you should be able to:
1. Describe main features of the **Big Bang Model** and the evidence supporting this model
2. Relate the rotation of stars in galaxies and the energy composition of the universe in terms **dark** and ordinary baryonic matter.
3. State the evidence for the expansion of the universe and describe the final fate of the universe
3. Explain how the **heavy elements** are created and distributed to planets
4. Describe how a **black hole** can be created by the explosion of a hypernova

Post-lesson assignment
Complete the following post-lesson assignment by 4th May 2010.





Pre-lecture tasks
The objective of the Pre-lesson quiz is to gauge your knowlege on some current terms and ideas in cosmology. Please complete the quiz baed on your current knowledge without doing any further research on the internet or books.



Describe main features of the Big Bang Model and the evidence supporting this model

Main features and evidence supporting the Big Bang
1. The universe is expanding
In 1929, Edwin Hubble discovered that light from far away stars are red-shifted. That means that they are moving away from us. The further a star is from us, the faster it is moving away. The data show that groups of galaxies are moving away from each other, like the debris of an explosion.
If galaxies are moving away from each other now, then by tracing the expansion back in time, there must be a moment when the universe collapses to a point object. Astronomical data collected by telescopes indicated that 13.7 billion years ago, the universe was a hot, dense place that exploded and has been expanding since.
2. The cosmic background radiation
If the universe began with a Big Bang, it must have produced very intense radiation. The remnants of this radiation, cooled by expansion, must still exist today. In 1964, Arno Panzias and Robert Wilson of Bell Laboratories were scanning the sky with a new radio receiver when they detected a faint, uniform crackling. What the researchers first assumed was static in their receiver turned out to be the radiation left over from the Big Bang. The radiation is a uniform glow of microwave radiation permeating space. This cosmic microwave background has exactly the temperature (2.73 K) if it was produced by a Big Bang that cooled steadily since that time. Penzias and Wilson were awarded the 1978 Nobel Prize in Physics for their discovery.
3. The cosmic abundance of Helium
Astromers found that the amount of helium among all the baryonic matter in the universe is 24 percent by mass. Nuclear reactions inside stars have not gone on long enough to produce this amount of helium. But theoretical models show that this amount of helium can be produced by the Big Bang.

Dark Matter
As far back as 1930s, astronomers found that the amount of visible matter in a rotating galaxy does not produce enough gravitational attraction to keep the stars from flying apart. There must be some invisible matter in the galaxy that provide the additional gravity. This invisible matter, known as dark matter, does not emit, reflect or absorb light. About a quarter of the universe is made of dark matter.

Expansion of the Universe and Dark Energy
Astronomers observed that the further a Type 1a supernovas in distance galaxies is from us, the faster it is moving away. This indicate that the expansion of the universe is accelerating and can be explained by a repulsive force pushing everything apart. The energy associated with the repulsive force is known as dark energy. Dark energy made up about 70 percent of the universe. If the universe keep on expanding, then sometime in the distance future, the other galaxies will be so far away that we will not be able to see them.

Heavy Elements Creation
The Big Bang theory can explain the relative abundances of Hydrogen and Helium in the universe. However, there is not enough time to create the heavier elements because the universe was expanding too rapidly after the Big Bang. When stars finally formed, the heat and pressure at the core of stars produces the other heavier elements through nuclear fusion. The heaviest element that nuclear fusion can create is iron. Elements heavier than iron were created by the high energy concentration during a supernova explosion. Second or third generation stars and planets that were form from the debris of the supernova will have the heavy elements with them.

Black Holes
Black holes are objects whose gravity is powerful that not even light itself can escape. Gravitational collapse occurs when a star's internal pressure due to its core temperature is insufficient to resist its own gravity. This can occur when the material for nuclear fusion is used up and the star is not able to maintain its temperature or when a star receives extra matter causing gravitational collapse. As a star collapses, the outer layers may be blown away and it may end up as a black hole if the mass of the remnant exceeds three to four solar masses.