## Astronomy Chapter 25

 In a galaxy collision, two similar-sized galaxies pass through each other with a combined relative velocity of 1700 km/s .If each galaxy is 100 kpc across, how long does the event last? 3.6×10^15 s The Andromeda Galaxy is approaching our Galaxy with a radial velocity of 120 km/s.Given the galaxies’ present separation of 800 kpc, and neglecting both the transverse component of the velocity and the effect of gravity in accelerating the motion, estimate when the two galaxies will collide. 2.07×10^17s Two galaxies are orbiting each other at a distance of 440 kpc . Their orbital period is estimated to be 33 billion years.Use Kepler’s law (as stated in Section 23.6 in the textbook) to find the total mass of the pair 6.86×10^11 solar masses How massive are the largest known galaxies? a trillion solar masses Based on galactic rotation curves and cluster dynamics, we think dark matter comprises over 90% of the entire mass of the universe. Collisions between galaxies is thought to be commonplace. The distance between adjacent galaxies in a typical cluster is about ________ times the size of a typical galaxy. five or less Due to the galaxy density and collisions, ________ are rare in the centers of clusters. spirals Collisions between galaxies cause the gas and dust clouds to collide, leading to rapid star formation. According to the HST data, very distant (and early) galaxies tend to be smaller, bluer, and more irregular than modern ones. A merger between two large galaxies of comparable size will most likely produce a large elliptical galaxy. A merger between a small elliptical galaxy and a large spiral galaxy will most likely result in a large spiral. The further away a galaxy is the longer ago it existed. The energy radiated from a typical quasar requires that its black hole accrete about: 10 solar masses per year. A galaxy is at a distance of one billion light years. Which of the following is true? We see the galaxy the way it was one billion years ago. A supernova occurred 10,000 years from now in a galaxy 50,000 light years away will be observed on Earth 40,000 years from now. What is the Great Wall? It is a large sheet of galaxies measuring 70 Mpc by 200 Mpc. Rotation curves for spiral galaxies show most have dark halos. As we look at larger and larger scales in the universe, we find a larger and larger percentage of the matter is dark. When spiral galaxies do collide, the impact is greatest on their: giant molecular clouds. Astronomers believe that a spiral galaxy may form from a collision between a small and large galaxy. ________ galaxies may bridge the gap between spiral galaxies and quasars. Seyfert Active galaxies are having their central engines temporarily fed by what occurrence? a close interaction with a neighboring galaxy If the merger theory is correct, the brightest active galactic nuclei should contain supermassive black holes. A supernova that occurred 30,000 years ago in a galaxy 100,000 light years away will be observed on Earth 70,000 years from now.