Astro Lab 4

The Solar System 1. Use an authoritative source to estimate what percentage of the mass of the Solar System is due to the Sun. Be sure to cite your source. Where is most of the mass in the Solar System? The most mass in the solar system is in the Sun, 99% (from TA) 2. Examine the plot below of the Solar System's rotation curve for the planets. Describe, in your own words, the features of this rotation curve. Be sure to address how the speeds of the inner planets (Mercury, Venus, Earth, Mars) compare to the outer planets (Jupiter, Saturn, Uranus, Neptune), and relate this pattern to how the Solar System's mass is distributed. The inner planets have similar distance from the sun but all have different and fast speeds, the outer planets move slower than the inner and move at different slower speeds. Galaxies 3. Pictured above is a spiral galaxy; it happens to be oriented facing us, so it's easy to see the patterns the stars and nebulae make. Based just on this image, where is most of the mass of this "face-on" spiral located? Do you expect this galaxy and the Solar System to have similar rotation curves? The most mass of this face on spiral is located in the center. The rotation curves can be expected to have similar curves due to Keplers Law 4. Unfortunately we can only find the rotation curves of spiral galaxies that are oriented "edge-on" to us, like those pictured below. Why is this? We are only able to find the rotation curves of spiral galaxies that are oriented edge on because you cannot measure the speed of face on spirals because of the lack of shifts. With edge on spirals we are given the Doppler Shift to calculate the velocity more precisely.

5. Examine the rotation curve for NGC 134, pictured at the bottom of this page. Superimposed on the rotation curve is an image of the galaxy, scaled to match the x-axis of the plot. Describe the features of NGC 134's's rotation curve. Then create a table like the one below, and record the galaxy's speed of rotation at each of the following radii, plus the largest radius for which you can estimate a reasonable speed ( we've done the first row for this question and the next for you ). Radius in arcseconds (") Speed (km/s) Interior Mass (M Sun ) 25" 80 3.2e^9 50" 200 4.0e^10 100" 235 1.1e^11 175’’ 250 2.2e^11 6. Calculate mass interior to each radius using the following equation and fill out your table. Be sure to use scientific notation for these large numbers. Is it reasonable to say that most of the mass of NGC 134 is in its center? Why or why not? M=1125 ⋅ D ⋅ r ⋅ v2 In this equation, M is the interior mass in solar masses, 1125 is a conversion factor that includes (big) G , D is the distance to the galaxy in Mpc, r is the distance from the center of the galaxy in arcseconds, and v is the speed of rotation (in km/s) at that radius. With NGC 134 the majority of the mass of the galaxy is not in the center because as the radius gets further away from the center of the galaxy, the objects increase in velocity and in mass. 7. Describe in your own words the distribution of mass in NGC 134. How would your estimate change if NGC 134 was not perfectly edge-on, in other words, if it was tilted with respect to our line of sight? The center of galaxy is not responsible for most of the mass in the center of the galaxy, this shows that there could be a high volume of dark matter in the disk of the galaxy. The dark matter is what creates the gravitational force of the galaxy and keeps the stars in orbit. If the galaxy was tilted with respect to our line of sight, this means that we would not be able to predict the velocity and mass of the objects in this orbit. 8. Estimate the mass of each of the other galaxies below using data you select from their rotation curves. Record the data from the plot you used, and why you chose