Cosmology PDF

Cosmology:Cosmology is the study of the universe-how it started, how it works,and how it might end. It looks at things like galaxies, stars and space to understand the universe’s big picture. Edwin Hubble: Edwin Hubble was an American astronomer who made ground breaking discoveries about the univer...

Cosmology:Cosmology is the study of the universe-how it started, how it works,and how it might end. It looks at things like galaxies, stars and space to understand the universe’s big picture. Edwin Hubble: Edwin Hubble was an American astronomer who made ground breaking discoveries about the universe. He showed that the universe is expanding by observing that distant galaxies are moving away from us, a discovery that supported the Big Band Theory. Red Shift:Red shift is when light from an object,like a galaxy,shifts to longer (redder) wavelengths as it moves away from us. This means the object is moving away and it helps scientists understand that the universe is expanding. The more red shafted the light,the faster the object is moving away. Blue shift: Blue shift is one example of the Doppler effect. It is the opposite effect to redshift. Doppler blueshift is caused by movement of a source towards the observer. The term applies to any decrease in wavelength caused by relative motion, even outside the visible spectrum. The doppler effect: Doppler effect in physics is defined as the increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move towards (or away from) each other. Cosmic microwave background radiation: The cosmic microwave background radiation is the faint remnant glow of the big bang. This false colour image, covering about 2.5 percent of the sky, shows fluctuations in the ionised gas that later condensed to make superclusters of galaxies. Galaxy: A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by gravity. Our galaxy, the Milky Way, also has a supermassive black hole in the middle. Black hole: A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying. Plasma: Plasma is superheated matter so hot that the electrons are ripped away from the atoms forming an ionised gas. It comprises over 99% of the visible universe. In the night sky, plasma glows in the form of stars, nebulas, and even the auroras that sometimes ripple above the north and south poles. The milky way: The Milky Way is a huge collection of stars, dust and gas. It's called a spiral galaxy because if you could view it from the top or bottom, it would look like a spinning pinwheel. The Sun is located on one of the spiral arms, about 25,000 light-years away from the centre of the galaxy. What is Gravity? Gravity is the force of attraction experienced between any two objects in the universe. It is the force that drives the universe. What is needed for Gravity to become significant as it is a weak force? These masses need to be incredibly large for the force to become significant. What happened within a star because of gravity? When one of the objects is as massive as a star,gravity can become an extremely strong force. It also creates pressures within the star so immense that the atoms of hydrogen at the star;s centre become fused together to form atoms of helium. What two opposing forces determine the structure of a star? The structure of any star is determined by the balance between two opposing forces. - The inwards forces of gravity. Which causes the material within the star to fall towards the centre. - The outwards force that results from pressure caused by the heat radiated from nuclear fusion in the star. This pressure is called radiation pressure. What is a nebula? Gravity is also responsible for creating stars from the huge interstellar gas known as nebulae. (cloud of gas) Describe how the sun was formed from a nebula: The Sun and the planets formed together, 4.6 billion years ago, from a cloud of gas and dust called the solar nebula. A shock wave from a nearby supernova explosion probably initiated the collapse of the solar nebula. The Sun formed in the centre, and the planets formed in a thin disk orbiting around it. Describe how galaxies form: Galaxies form out of immense clouds of gas that collapse and rotate. As they evolve, stars form within them. Entire galaxies can collide, changing their appearance. Looking deep into space, we see galaxies at earlier stages in their lives, and learn more about their evolution. How many stars do galaxies contain? The size of galaxies vary greatly but all galaxies contain an enormously large number of stars,usually between 10 million and a hundred million. What is significant about the gravitational field of a black hole? A black hole forms when the mass of an object, like a star, suddenly collapses down to a tiny volume. A small object with a large mass causes a gaping dent in space time. This enormous warp creates a gravitational field so strong that nothing, not even light, can escape from it. How are black holes detected? By detecting the gravitational ripples when they collide. We can also detect black holes by detecting the ripples in space-time created when two of them crash into each other. From that signal, we can tell how massive the black holes were, how far away they were, and how fast they were travelling when they collided. What is believed to be at the centre of most galaxies? How big are they? Black holes are a class of astronomical objects that have undergone gravitational collapse, leaving behind spheroidal regions of space from which nothing can escape, including light. Observational evidence indicates that almost every large galaxy has a supermassive black hole at its centre. Where do stars come from? Stars are formed from nebulae which are giant clouds of helium gas and other particles. The most well known nebula which can be seen with the naked eye is a near orion. When the clouds contract forming a heavier company, clouds and the temperature decrease. - Plasma is a collection of charged particles that resembles a gas. Stars are seldom born alone. - Usually these massive reactions create many clusters of stars - The brightest clusters can be seen in the southern hemisphere The life of a star: Once a star stops condensing the star begins to burn at a steady rate which depends on what it is made of. At this stage it is called a main sequence star. - Main sequence stars grow brighter and brighter, all the time undergoing the nuclear reaction of converting hydrogen to energy and helium. Nova: a star showing a sudden large increase in brightness and then slowly returning to its original state over a few months. What is a protostar? A young star, a star that's forming? The fate of a Star: How can astronomers observe neutron stars? - by detecting pulse What is the major fuel used by stars in the process of fusion?- Hydrogen What is one way astronomers can differentiate between a pulsar from a normal star? Normal stars don’t pulse Neutron Star: A neutron star is a very dense,rotating object that emits electromagnetic radiation and is called a pulsar Black Hole: A black hole is a body with an immensely strong gravitational field. What is meant by very low luminosity? Dim low light Red Giant: A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses in a late phase of stellar evolution. White dwarf: A white dwarf is what stars like the Sun become after they have exhausted their nuclear fuel. (white stars are difficult to observe because they have very low luminosity) Black dwarf: A black dwarf is a theoretical stellar remnant, specifically a white dwarf that has cooled sufficiently to no longer emit significant heat or light. What did Lemaitre propose the universe was doing? He was the first to propose the modern Big Bang Theory, the theory that the universe began from the explosion of a small original super atom. Big Bang Theory: The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. The notion of an expanding universe was first scientifically originated by physicist Alexander Friedmann in 1922 with the mathematical derivation of the Friedmann equations.