Q1.Week1a.Formation of Heavier Elements.pptx
- 1. Formation of the Heavier Elements -Stellar Nucleosynthesis
- 2. Nucleosynthesis •Nucleosynthesis is the process of element (nuclei) formation. •Three types: Big Bang nucleosynthesis Stellar (star) nucleosynthesis Supernova nucleosynthesis •Today, only stellar and supernova nucleosynthesis are occurring in our universe. •Element formation in our universe relies on nuclear fusion reactions. (fusion = come together)
- 3. The Big Bang •The Big Bang Theory is the most widely accepted scientific theory about the origin of the universe. It is supported by multiple lines of evidence. •The “Big Bang” was a phenomenally energetic explosion that initiated the expansion of the universe.
- 4. The Big Bang •At the moment prior to the Big Bang explosion, all matter and energy were compressed at a single point (a singularity – a point of infinite density). •We do not know what was before…..? •The universe has been expanding ever since, with galaxies moving farther and farther apart.
- 5. The Big Bang •Using the rates of expansion measured in the universe and astronomical distances, the age of the universe can be calculated back to the time of the Big Bang. The age of the universe is calculated at about 13.7 billion years old. By contrast, our Sun and its surrounding planets (i.e. our Solar System) is 4.65 billion years old.
- 6. Big Bang Nucleosynthesis •All Hydrogen and most Helium in the universe was produced during the Big Bang Event, starting ~100 seconds after the explosion. A small amount of Lithium and Beryllium were also produced.
- 8. •Formation of heavier elements started million years after big bang explosion
- 9. •A vast cloud of gas and dust called NEBULA start to collapsed due to gravity
- 10. • Hundred thousand years later gravity pulled the clouds together creating a PROTOSTAR • In the center where molecules crashed pressure and temperature rise up incredibly the PROTOSTAR becomes hot enough for nuclear fusion to occur starting the process called STELLAR NUCLEOSYNTHESIS
- 12. Stellar Nucleosynthesis •The first fusion process occurs in the hydrogen core of stars such as the sun with a temperature of less than 15 million K are called main-sequence stars.
- 13. Stellar Nucleosynthesis •The basic nuclear reaction in the Sun converts hydrogen to helium and releases energy in the form of electromagnetic radiation. This is why our Sun shines! •Our Sun is only large enough to fuse hydrogen into helium within its core.
- 14. Nuclear fusion releases tremendous amount of light, heat and radioactive energy.
- 15. •Since He is heavier than H, and as more and more H is burn into He, the core of a star becomes comprise of He as H is depleted.
- 16. •A star with a very dense helium core and a hydrogen shell expands into a red giant due to increased radiation pressure.
- 17. •Due to this process, the temperature and density of the core of the star increases up to 100 million K. The star’s thermal pressure causes it to push out H gas. The star balloons into a red giant.
- 18. Supernova explosion releases a tremendous amount of energy enough to synthesize elements heavier than iron. Examples of these elements are uranium and thorium, which are some of the heaviest known elements
- 20. This is done through the r- process that involves rapid capture of neutrons by the atom.
- 21. Other heavy elements are also synthesized through s- process involving slow neutron capture in red giants.