Question

1. What objects Hershel and Shapley, respectively, used to map the Galaxy? What were their results and why did they come up with such different dimensions of our Galaxy?

2. What are the four major parts of our galaxy? Summarize their main properties? What type of orbital motion do the objects exhibit in each part?
3. At the center of our Milky Way Galaxy, there is a supermassive black hole. Infrared observations show that a star that has mass ~ 100 M⦿, orbits around this black hole once every 14.5 years on an elliptical orbit with a semi-major axis a = 920 AU. Estimate the mass of this black hole at the Galactic center.
4. The Sun moves around the Galactic center in a nearly circular orbit with the radius R0 ~ 8 kpc at the orbital velocity v0 ~ 220 km s−1. The total mass of the Galaxy within the Sun’s orbit is MG. The observed Galactic rotation curve shows an orbital velocity of stars v ~ 270 km/s at near the outer boundary of the visible Galactic disk (d ~ 16 kpc from the Galactic center). Calculate the total Galactic mass between the Sun’s orbit and the outer boundary of the Galactic disk in units of MG.
5. The Sun orbits around the Galactic center at the distance of d0 = 8 kpc with a velocity of v0 = 220 km s−1. Assuming that the mass beyond the solar orbit along the Galactic disk is negligible compared to that within the solar orbit, what rotational velocity would be expected for a star orbiting at the distance of d = 16 kpc from the Galactic center?
6. Using Cepheid variables, Edwin Hubble measured the distance to many spiral nebulae, for example he measured the distance ~ 300 kpc for Andromeda Nebula. This marks a historic discovery. What is the astronomical significance of this measurement?
7. You observed a galaxy where you found no current star-forming activity. Would you expect that there are neutron stars in this galaxy? Justify your answer.
8. Explain what dark matter is and how it was discovered in our and other galaxies.
9. What are the three major types of galaxies? Rank them from a) smallest range of sizes to largest range of sizes, b) no new star formation to vigorous star formation, c) bluish to yellow-whitish to reddish, d) mostly population I to mostly population II stars. (You should know what are population I and II type stars.)

Answer 1

Answer:1. The Milky Way Galaxy surrounds us, and you might think it is easy to study because it is so close. However, the very fact that we are embedded within it presents a difficult challenge. Suppose you were given the task of mapping New York City. You could do a much better job from a helicopter flying over the city than you could if you were standing in Times Square. Similarly, it would be easier to map our Galaxy if we could only get a little way outside it, but instead we are trapped inside and way out in its suburbs—far from the galactic equivalent of Times Square.

Step-by-step explanation: