Learning Objectives At the end of this unit you should be able to; Explain the major events in the evolution of the universe according to the Big Bang Theory, in chronological order, backing up your arguments with observational evidence Describe the lifecycle of a star in chronological order and explain the main stages, relating the stellar evolution to initial mass Describe the main features of the solar system using correct scientific terminology, placing objects in the correct order of distance from the sun. It is human nature to ask the big questions such as what is our position within the universe. Prior to the mid 1500 s the answer to this question would have been dominated by religion, and the view that we are the center of all things, and thus the observable solar system such as the sun and the planets orbit the Earth. It was not until 1543 that Nicolaus Copernicus put forward the idea that the planets of the solar system, including the Earth, orbit the sun. In 1687 Newton used his laws of gravitation to describe large-scale movement within the solar system (and Universe), strengthening Copernicus s argument. Interestingly however, the realisation that our sun was indeed a star was not made until the 1860 s, when a Jesuit priest, Father Angelo Secchi, compared the spectral lines of the sun with other stars. Key Facts and Principles. 0.1s after the big bang; The universe had expanded and cooled to 10 12 K Only subatomic particles such as electrons and quarks (quarks are the sub atomic particles from which protons and neutrons are made) could exist. 100s after the big bang; The temperature had reduced (10 8 K) Subatomic particle energy was such that quarks could come together, forming protons and neutrons.
100,000 years after the big bang; The universe continued to expand and cool. Ionized hydrogen and helium gas form. Separation distances between particles became larger. The universe became transparent to radiation. Cosmic microwave background radiation emitted. Stable, neutral atoms of hydrogen and helium form at the end of this period. 100 million years after the big bang; Hydrogen and helium gas reduced in energy sufficiently for gravity to take over, condensing the gas increasing its temperature. When these condensed regions of gas reached sufficient temperatures, fusion reactions take place and the first few stars (emitting the first light in the universe) formed. This period is known as the cosmic dawn. Stars are formed within giant hydrogen gas and dust clouds called nebulae. Clumps of gas and dust contract under gravitational forces to form a protostar. As the protostar continues to contract under gravity it heats up until there is enough energy to initiate a fusion chain reaction, igniting the star. The lifecycle of the star is predetermined by the mass of the star. For a star of 1.5 solar masses (1.5 times the size of our own sun or less); The hydrogen within the star is fused together to form helium, releasing energy. The star expands due to the heat energy released in the fusion reaction, until the thermal expansion balances out the gravitational contraction.
The stable burning period is called the main sequence. The star remains in this phase for around 10 billion years, continually turning hydrogen into helium. As the hydrogen in the core begins to run out, the fusion reaction slows and the thermal energy reduces. The thermal expansion no longer overcomes the force of gravity and the core contracts. The fusion reactions shift toward the outer shell of the star The outer shell of the star expands, becoming larger and cooler. The star has now reached the red giant phase. Eventually the helium in the core runs out. The outer shell of the red giant drifts away from the core to form a planetary nebulae. The core of the star shrinks under gravity forming a white dwarf. The white dwarf cools and becomes a black dwarf. If the star is above 1.5 solar masses Large stars use up all the hydrogen in the core within 1 million years. The core shrinks and the outer layer expands, forming a red super giant. The core of the red super giant starts fusing helium to form carbon. Then the carbon is fused to form oxygen and so on, the series of fusion reactions placing layers of heavier and heavier elements down on the core. The fuel runs out and the stars core goes out, collapsing in on itself. The core explodes in a supernovae Sometimes part of the stars core survives the supernovae as a core remnant. Core remnant less than 1.5 solar masses - black dwarf Core remnant is between 1.5 and 3 solar masses neutron star Core remnant greater than 3 solar masses black hole
The Solar System is a system of objects that orbit the Sun in either circular or elliptical motion, bound by gravity. The planets of the solar system are: Mercury, Venus, Earth and Mars The Inner Planets since they are closest to the Sun. Terrestrial Planets because they all comprise of rock and metal. Venus, Earth and Mars have substantial atmospheres Mercury has virtually no atmosphere. The Earth has one natural satellite, the moon Mars has two moons, Deimos and Phobos. Jupiter, Saturn, Uranus, Neptune The Outer Planets Also known as the Jovian Planets or Jupiter like giant planets. Jupiter and Saturn are Gas Giants Uranus and Neptune are Ice Giants Jupiter is the largest planet in the solar system. Its four largest moons, Io, Europa, Ganymede, and Callisto are collectively known as the Galilean moons. Saturn is 95 times the size of the Earth and probably has a rocky core. Pluto is 39 AU from the Sun. Pluto used to be considered the ninth planet of the solar system but was downgraded to a dwarf planet in 2006. An easy way to remember the order of the planets (including the dwarf planet Pluto) is the mnemonic My Very Easy Method Just Speeds Up Naming Planets, to give Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
Glossary Fusion A reaction in which light atoms are fused together to form heavier atoms, releasing energy in the process Interstellar Occurring or situated between stars Ionised A formerly neutral atom that has become charged, typically through the removal of an electron Jovian Relating to the class of planet to which Jupiter belongs, derived from being of or like the god Jove (Jupiter). Main Sequence The stable hydrogen burning phase of a star. Quark a sub atomic particle of multiple types, all containing a magnitude of charge equal to 1/3 that of the charge on an electron. The building blocks of protons and neutrons. Retrograde directed or moving backwards. Singularity a one-dimensional point that contains a huge mass in an infinitely small space, where density and gravity become infinite. Subatomic smaller than or occurring within an atom. Terrestrial on or relating to the planet Earth.