Astro 1109 In-class writing exercise: Synthesizing Information 1. Use each of the following sections of text from our readings. Don’t quote, but don’t plagiarize (i.e. you can’t ‘steal’ nice little phrases). 2. First, summarize each section in 4 sentences by paraphrasing. 3. Next, summarize each section in 2 sentences. 4. Next, summarize each section in only one sentence. 5. Finally, create a “headline” for each section of text. 1. From Pedro Ferreira’s The State of the Universe, page 177: “The evidence for an invisible halo of mass is not unique to our galaxy. During the 1970s, a group of astronomers looked in some detail at other galaxies. These galaxies are quite far away, and it is difficult to measure the velocity of individual stars within them. Each individual galaxy is scanned from one tip to the other, and the spectrum of light at each point measured. By looking at each spectrum and measuring the Doppler shift, it is possible to find out if that particular bit of the galaxy is moving away from us or towards us. Not only that, we can find out how fast each bit of the galaxy is moving. By plotting the velocity as a function of radius, we end up with rotation curves, and once again we find the same thing. The velocity of rotation of each galaxy stars constant well into its outer regions. Each galaxy seems to have a halo of invisible matter just like our own.” 2. From “Dark and Darker” by Neil de Grasse Tyson: “When nothing else works, scientists sometimes question the foundations of their assumptions. In the early 1980s the physicist Mordehai Milgrom of the Weizmann Institute of Science in Rehovot, Israel, proposed a new twist to Newton's law of gravity: modified Newtonian dynamics, affectionately called MOND. Admitting that standard Newtonian dynamics works just fine on the scale of stars and planets, Milgrom suggested that Newton needed help at the scale of galaxies and galaxy clusters. His solution was to add a term to Newton's equation--a term mathematically rigged to come to life only when applied to great distances. Although the term was intended primarily as a computational tool, Milgrom didn't rule out the possibility that it referred to an unheralded phenomenon of nature. MOND enjoyed some success describing isolated spiral galaxies, but it was not conceived as a complete theory of gravity, and so it lacks a mechanism for calculating the motions of more complex systems, such as multiple galaxies. More important, MOND jumps through hoops to say anything about the early universe, where galaxies had not yet formed. In early 2003 NASA published a portrait of the cosmic microwave background made by the Wilkinson Microwave Anisotropy Probe (WMAP); that image, combined with data from other telescopes, isolated and measured the effects of darkmatter in the early universe leaving MOND with nothing to contribute, awaiting a likely burial in the graveyard of creative but wrong ideas. 3. From Dark Cosmos by Dan Hooper, page 98-99: “In the simplest variety of supersymmetric models, there are seven superpartners that are potentially interesting candidates for dark matter. Three of these are sneutrinos, the supersymmetric partners of the Standard Model neutrinos. The other four are the superpartners of the photon, the Z boson, and two Higgs bosons. Those particles, respectively, are the photino, the zino, and two Higgsinos. These four are collectively known as neutralinos. In many supersymmetric models, the lightest of the four neutralinos is the lightest of the superpartners. Which one this might be is not simply answered. Our understanding of neutralinos is complicated by the fact that each neutralino need not be simply one of these four particles, but instead can be some combination of them. For example, one of the four neutralinos could be half of the superpartner of the photon and half the superpartner of the Z. Another could be 99 percent Higgsino, half a percent photino, and another half a percent zino. Any combination is possible, as long as the four particles add up to a complete set of photino, zino, and both Higgsinos. This is like being told that there are four dogs of four breeds you are looking for: a German shepherd, a beagle, a golden retriever, and a toy poodle. To complicate things, these four dogs can be mixed breeds as long as the sum of the four dogs is precisely one German shepherd, one beagle, one golden retriever, and one toy poodle. There could be four pure breeds. On the other hand, two could be one-quarter German shepherd, one-quarter beagle, and half toy poodle, while another is purebred golden retriever, and another is half German shepherd and half beagle. The possible combinations are