Astronomy Exam 3 study guide
Astronomy Exam 3 study guide astronomy 113
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This 9 page Study Guide was uploaded by Morgan Owens on Monday April 11, 2016. The Study Guide belongs to astronomy 113 at George Mason University taught by Pesce in Winter 2016. Since its upload, it has received 533 views.
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Date Created: 04/11/16
Astro 113 Exam #3 Review 1. What is black hole a supported by? A black hole is not supported by anything it’s simply a gravitational force with no volume and infinite density. 2. What are the properties of a black hole? A black hole has properties of mass, angular momentum and electric charge. Its center is called the ‘singularity’ which is the point of infinite density where laws of physics are likely to break down, surrounded by the ‘event horizon’. The event horizon is the ‘point of no return’ where once matter has passed this point there is no coming back out. Black holes are measured from their singularity to their event horizon, which is known as the Schwarzschild Radius. Lastly, outside the event horizon is the accretion disk which is a rapidly rotating disk of gas surrounding a black hole that attracts matter. 3. Black holes do not emit radiation, how do we measure their gravitational forces and mass? By matter orbiting the black hold and the speed of the matter in the accretion disk. Or xray flickering, which occurs when matter interacts with the accretion disk and the friction between the two start to heat up, it then emits xrays which are detectable from Earth and can help us measure mass. 4. The Xrays that imply the presence of a black hole come from where? The fiction between the matter entering the black hole and the accretion disk. The closer matter gets the hotter it gets and then it releases electromagnetic radiation. 5. What are candidates for dark matter? Over 90% of the mass in the galaxy, but not quite sure what it is exactly. Could be: black holes: a region of space having a gravitational field so strong that no matter or radiation can escape. brown dwarfs: a celestial object intermediate in size between a giant planet and a small star, believes to emit mainly infrared radiation. neutrinos: a neutral subatomic particle with a mass close to zero and half integral spin, rarely interacting with normal matter. subatomic particles (WIMP, weakly interacting massive particle) a hypothetical particle that would interact via the electromagnetic force. 6. The most common type of Elliptical galaxy is a what? Dwarf elliptical galaxy. 7. The Doppler shift recorded for almost all galaxies is what? Red shift, Hubble observed galaxy spectral lines shifted to red, means that they are moving away from us, or we are moving away from them. Redshift is linked to recessional velocity (z), measure distance (D) with Cepheid’s or Supernova, Hubble’s Law: recessional velocity is proportional to distance. 8. Star formation is currently absent in which galaxies? SO galaxies and elliptical galaxies. 9. Quasar active regions are estimated to be the size of what? The active portion of a Quasar galaxy is about the size of our solar system. 10. Which object are examples of active galaxies? An active galaxy is defined as: a galaxy that has a active galactic nucleus (AGN) in the center of the galaxy that has an abnormally high luminosity rate across the EM spectrum. EX: quasars, radio galaxies, BL Lacerta objects, Seyfert galaxies. 11. What is the surface around a black hole from within which no matter or radiation can escape? Event horizon. 12. Galaxies are classified by type according to what property? They are classified by their shapes and visual appearance, such as disk, spirals, overall shape. Spiral galaxies are spiral shaped, elliptical galaxy has no spiral or disk, its ellipsoid shape, and irregular galaxies have no real shape. 13. Classification of spiral galaxies into types is based on the tightness of what? Tightness of their spirals. 14. Galactic disks owe their blue color to what? The many young bright blue stars inside them. 15. Elliptical galaxies have generally been thought to have no what? They generally have no star formation. 16. What is the Local Group? A Local Group is a cluster of galaxies nearby and in our own galaxy, about 30 of them. 17. Every nearby rich cluster is located in a larger cluster of clusters called a what? Clusters of clusters are called ‘superclusters’. 18. In 1929, Hubble announced the distance a galaxy is from us is directly proportional to its what? Hubble’s Law, Vr = Ho * D, recessional velocity = Hubble’s constant * Distance 19. Where do new stars form in our Galaxy? They form inside the arms of our galaxy. 20. One of the implications of Hubble's Law is that the universe is what? That our galaxy is expanding. 21. What is galactic cannibalism? When a larger galaxy absorbs a smaller one. 22. Why are spiral arms a good site for the formation of new stars? They are a good site for the formation of new stars because of the density and compression of matter inside them. 23. Galaxies that radiate much more strongly at radio and Xray wavelengths than other galaxies are called what? A Radio Galaxy 24. What type of structure do many radio galaxies exhibit? An enormous doublelobed radio structure. 25. What does the electromagnetic radiation of quasars exhibit? Extremely powerful emission across all the wavelengths, most of which are radio and xray waves. The emission lines are also very strong. 26. The stars in an elliptical galaxy, as a population, are more similar to those in what part of a spiral galaxy? Stars in an elliptical galaxy are similar to those within the halo and bulge: red, old and long lived. 27. According to current consensus, quasars must have what at their centers? A super massive black hole. 28. What fuels quasars found nearby? They consume gas and dust, some of the largest ones consuming the equivalent of 600 Earths per minute. 29. What component is thought to dominate the mass of the Universe? Dark matter. 30. What causes the hot gas between galaxies in clusters? It’s a result of galactic collisions. While the stars of colliding galaxies do not interact, their gas and dust do, which heats up and ejects the matter into the intracluster medium. 31. What type of stars is found in the halo of our galaxy? Old red stars. 32. The region of the sky called the “Milky Way” has a larger concentration of stars than other regions. Why? It has a higher concentration of stars because of the angular momentum of the disk shape. The stars tend to align in the same plane. 33. Distant quasars can be used as a light source to study the properties of what? Can be used to study the distribution and chemical composition of the matter in the universe. 34. What is Hubble's law? The recessional velocity of a galaxy is proportion to its distance to us. Vr=Ho*D 35. What can we study with gravitational lensing? Dark matter, distant stars and exoplanets. 36. What kind of electromagnetic radiation most easily penetrates interstellar dust? Infrared radiation. 37. If a galaxy spectrum shows a redshift corresponding to a radial velocity of 1500 km/s, and H = 75 (km/s)/Mpc, how far away is the galaxy? Thus d=Vr/Ho which is D=(1500 km/s)/ ([75 km/s]/Mpc) which equals 20 Mpc. 38. The distance from the Sun to the center of our Galaxy is how far? About 8 kpc, kiloparsecs. 39. Where is our Sun located in the Galaxy? It is located at the inner edge of the Orion Arm of the Milky Way galaxy. 40. What is 90% of the mass of the universe? And how do we detect it? Dark matter, and we detect it through its gravitational influence. 41. Suppose the Hubble's constant H = 60 (km/s)/Mpc. A certain galaxy is known to be 100 Mpc from the Milky Way Galaxy. According to Hubble's law, how fast will we see this galaxy to be moving? Vr=Ho*D Vr=([60km/s]/Mps)*100 Mpc Vr=6000 km/s 42. A galaxy is at a distance of one billion light years. What does that mean? That we see it as it was 1 billion years ago or that it is 306 Mpc away. 43. What is so important about Cepheid variable stars? Cepheid variable stars, which are stars that vary in temperature and diameter to change in brightness within a period. They are important due to being good distance indicators for making galactic and extragalactic scales. 44. Where in our Galaxy do we find the youngest stars? In the spiral arms. 45. What happens when galaxies collide? Density high in clusters: galaxies collide with each other all the time, because they space between stars is so big the stars basically pass through each other, but the gas and the dust clouds do not ( they are dispersed) dust and gas tends to smash together. Either gas is stripped out from individual galaxies, heated and added to the cluster (intracluster medium) HOT. Or stars are formed Galaxy mergers: similar sized galaxy merge together 46. What does our Galaxy's rotation curve tell us about it’s mass? It tells us the mass of the galaxy is about 10^11 times the mass of the sun and is filled with dark matter. 47. What is the Cosmological Principle? The distribution of matter in the universe is homogeneous and isotropic when seen on a large enough scale, forces should act uniformly through the universe. 48. Describe the motions of most stars in the disk of our Galaxy. Most are young, short lived bright blue stars. 49. What kind of galaxy is the Milky Way? Barred spiral galaxy. Poor galaxy, largest member of local group (poor cluster with ~30 galaxies) 50. Elliptical galaxies consist almost entirely of an old stellar component. What are the implications of this? Because elliptical galaxies consist almost entirely of an old stellar component it makes us believe that elliptical galaxies are the ‘ending result’ of a galaxies life. But some sources show that elliptical galaxies are the result of galactic collisions. Notes: Rich cluster: elliptical galaxies, thousands of galaxies in these clusters, the spiral galaxies in these clusters all have something funky, first of all there are very few of them, and then the rich environment has so many mergers that the spiral galaxies are interacting with each other and share common stars and make them look funny. Super cluster: you can see where the rich clusters are and where the voids are. Gravitational lensing: The farther away galaxies are moving away from us faster, evidence that the universe is expanding.
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