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Thursday, May 02, 2013
Jessie Horn: Chapter 14 Quiz
What does our galaxy look like? The Milky Way Galaxy consists of a thin disk about 100,000 light years in diameter with a central bulge and a spherical region called the halo that surrounds the entire disk. The disk contains most of the gas and dust of the interstellar medium, while the halo contains only a small amount of hot gas and virtually no cold gas.
How do stars orbit in our galaxy? Stars in the disk all orbit the galactic center in about the same plane and in the same direction. Halo and bulge stars also orbit the center of the galaxy, but their orbits are randomly inclined to the disk of the galaxy. Orbital motions of stars allow us to determine the distribution of mass in our galaxy.
How is gas recycled in our galaxy? Stars are born from the gravitational collapse of gas clumps in molecular clouds. Massive stars explode as supernovae when they die, creating hot bubbles in the interstellar medium that contain the new elements made by these stars. Eventually, this gas cools and mixes with the interstellar medium, turning into atomic hydrogen gas and then cooling further, producing star-forming molecular clouds. We call this process the star-gas-star cycle.
Where do stars tend to form in our galaxy? Active star forming regions, marked by the presence of hot, massive stars and ionization nebulae, are found mostly in spiral arms. In each arm, a spiral density wave causes gas clouds to crash into each other and to form clusters of new stars.
What do halo stars tell us about our galaxy's history? The halo generally contains only old, low mass stars that have a much smaller proportion of heavy elements than stars in the disk. Halo stars therefore must have formed early in the galaxy's history, before the gas settled into a disk.
How did our galaxy form? Halo stars probably formed in several different protogalactic clouds of hydrogen and helium gas. Gravity pulled those clouds together to form a single larger one. The collapse of this cloud continued until it formed a spinning disk around the galactic center. Stars have formed continuously in the disk since that time, but stars no longer form in the halo.
What lies in the center of our galaxy? Motions of stars near the center of our galaxy suggest that it contains a black hole about 4 million times as massive as the Sun. The black hole appears to be powering a bright source of radio emission known as Sgr A*.
Who is Andrea M. Ghez?is an American astronomer and professor in the Department of Physics and Astronomy at UCLA.
Who observed stars moving close to the speed of light in the center of our galaxy? Andrea M. Ghez
Where was Dr. Ghez born? New York City, New York. June 16, 1965.