The Differences Between Galactic and Globular Clusters - Assignment Example

Written Assignment 4 Describe how Harlow-Shapley determined that the sun was not at the center of our galaxy. Harlow-Shapley studied the position of globular clusters so that he could locate the location of the sun, which according to him, should have at the middle of the Milky Way. However, he found that he was wrong after he observed that the sun was in fact located on a spiral arm on the galaxy (Sparke and Gallagher, 2000). 2.    Compare the differences between galactic and globular clusters. Globular clusters are older and contain many more stars than galactic clusters. The stars in the globular clusters are denser than those found in the galactic clusters. Globular clusters are located within the halo of a galaxy while galactic clusters are found in the galaxy’s disk. The shape of galactic clusters is somewhat dissipated while that of globular clusters is symmetrically spherical (Seeds and Backman, 2010). 3. How does the use of H II regions to find a galaxys distance differ from the use of Cepheid variables? Cepheid variables are a group of brightly shining stars. They have a unique property where their absolute luminosity is directly related to their period. Once the absolute luminosity is known, then it is quite easy to find the distance by comparing with the known luminosity (Baryshev and Teerikorpi, 2002). Some of the challenges faced by astronomers when they are using Cepheid variables to find a galaxy’s distance include the fact that it is difficult to ascertain the linearity and nature of the relation in period-luminosity in different passbands. It is further complicated by metallicity’s effects on the slope and zero-point for the relation in period-luminosity of various passbands. There is also the factor of the changing extinction law and photometric contamination effects on the various distances from extragalactic Cepheids. according to recent data, the Cepheid variable period-luminosity relation is in the form of: = -3.53 log P + 2.13 ( - ) + φ where φ ~ -2.25 is a zero point, P is in days and Brackets = average of the light curve’s cycle (Seeds and Backman, 2010). H II regions are those regions that consist of ionized hydrogen. Their luminosity stems from the fact that this is where there is active star formation in the galaxy. An empirical relation exists between the geometrical size of the brightest H II region and the absolute magnitude of a galaxy. Another relation also exists between the rotational velocity of a galaxy’s H II regions and its luminosity. This relation is also known as the Tully-Fisher relation (Jones, Lambourne and Adams, 2004). 4.    How does the cluster method tell us the mass of galaxies? The cluster method of determining the mass of galaxies normally depends on the movement of galaxies within a particular cluster. When radial velocities in multiple galaxies in a cluster are measured, the result would be some velocities being larger than others. To calculate the mass of a galaxy, one needs to determine the size of a cluster that would remain together with a certain range of velocities. The total mass of the cluster is divided by the number of galaxies found in the cluster to get an average galaxy mass. This method assumes that the cluster is held together by its own gravity, therefore it will not fly apart (Seeds and Backman, 2010). 5.    What evidence do we have that the center of our galaxy is a powerful source of energy? There is a radio telescope map that shows that the Milky Way is a powerful source of energy. This instruments show that there is a huge amount of infrared and radio energy being emitted from the direction towards the center of the galaxy (Seeds, 2007). However, it has been found that the energy does not come from black hole believed to be centrally placed on our galaxy; instead, it comes from a gigantic whirlpool of dust, hot gas and other particles falling into the black hole. This swirling whirlpool is known as the accretion disk (Baryshev and Teerikorpi, 2002). 6. Our galaxy is not a radio galaxy, but it does emit radio energy. Explain where this radio energy comes from. The Milky Way is a regular galaxy but it does emit radio energy. This energy comes from Sagitarrius A* that is found at the galaxy’s center. The radiation is thought to be caused by a massive black hole found in the same area (Sparke and Gallagher, 2000). 7. Why should we expect quasars to be small? How small? Quasar is the short form of quasi-stellar radio source. Quasars are small since they normally display rapid changes in luminosity. These changes are immensely rapid in the optical range and in X-rays. The small size of a quasar can explained by the argument that the size of a luminous and variable object cannot be bigger than the distance which light travels in its variation time. This means that if the object in question has a significant variable in brightness over a week, then it cannot be bigger in size than a light-week. The average size of a quasar is approximately 10 to 10,000 larger than the Schwarzschild radius of our galaxy’s black hole (Seeds, 2007). 8. What observational evidence do we have that quasars are at the centers of very distant galaxies? Quasar observation began in the late 1950s. Optical lences were used to observe the faint blue points of light which were later identified as quasars. Scientists ananlyzed the light from the quasars and discovered that the objects were moving away from the earth at a high velocity. This was explained by their very large redshifts. These redshifts are the observational evidence that quasars are very far (Sparke and Gallagher, 2000). Quasars produce large volumes of energy, although they are thought to be radio-quiet. This energy which is visible from the earth, is thought to be from the quasars which are immense black holes found in the centers of distant galaxies. When materials spiral in the quasars, the mass is changed into energy. This is the energy that is visible from the earth (Jones, Lambourne and Adams, 2004). References Baryshev, Y. and Teerikorpi, P. (2002). Discovery of cosmic fractals. Hackensack, NJ: World Scientific Publishing Co., Inc. Jones, M.H., Lambourne, R.J. and Adams, D.J. (2004). An Introduction to galaxies and cosmology. Cambridge: Cambridge University Press Seeds, M.A. (2007). Stars and galaxies. Pacific Grove, CA: Thomson-Brooks/Cole Seeds, M.A. and Backman, D. (2010). Astronomy: The solar system and beyond. London: Cengage Learning Sparke, L.S. and Gallagher, J.S. (2000). Galaxies in the universe: An introduction. Cambridge: Cambridge University Press Read More