HW 15 -- CH 25
Where do you find the oldest star in the Milky Way Galaxy?
in the galaitc halo
nuclear bulge
the central (round) part of the Milk Way Galaxy
The Sun is located in the __________.
Orion arm
~13 billion years
Stellar Halo
population I star
a star containing heavy elements; typically young and found in the disk
population II star
a star with very low abundance of heavy elements; found throughout the Galaxy
Studies of the motions of the most remote globular clusters and the small galaxies that orbit our own Galaxy show that the total mass of the Galaxy is at least 2 × 1012 MSun, which is about ______ times greater than the amount of luminous matter, which astronomer have come to call dark matter
20
Observations show that dark matter must also be present in other galaxies (whose outer regions also orbit too fast "for their own good"—they also have flat rotation curves). Perhaps as much as _______ of the mass in our Galaxy (and many other galaxies) is not only invisible, but we do not even know what it is made of.
95%
In about 3 billion years, the Milky Way Galaxy and ___________ Galaxy will begin a long process of colliding, separating, and then coming back together to form an elliptical galaxy
Andromeda
The name of the supermassive black hole at the center of our Milky Way Galaxy.
Sagittarius A*
Very low heavier-element abundance
Stellar Halo (Excludes Dark Matter)
Very low rotation
Stellar Halo (Excludes Dark Matter)
The band of light encircling the sky, which is due to the many stars and diffuse nebulae lying near the plane of the Milky Way Galaxy
The Milky Way Galaxy
Intermediate heavier-element abundance
Thick Disk
Intermediate rotation
Thick Disk
~11 bllion years
Thick Disk
1 to ~10 billion years
Thin Disk
High heavier-element abundance
Thin Disk
High rotation
Thin Disk
nonluminous mass, whose presence can be inferred only because of its gravitational influence on luminous matter; the composition of this matter is not known.
dark matter
The fact that different parts of the Galaxy turn at different rates, since the parts of the Galaxy follow Kepler's third law: more distant objects take longer to complete one full orbit around the center of the Galaxy
differential galactic rotation
The Sun, like all the other stars in the Galaxy, orbits the center of the Milky Way. The Sun has a nearly circular orbit as it goes around the center of the Milky Way Galaxy, and lies in the Galaxy's disk. The speed of the Sun in its orbit is ~200 kilometers per second, which means it takes us approximately 225 million years to go once around the center of the Galaxy. We call the period of the Sun's revolution the __________. During the entire lifetime of Earth, only ~20 galactic years have passed.
galactic year
The stars in the halo are old, have low abundances of elements heavier than hydrogen and helium, and have ____________ orbits randomly oriented in direction.
highly elliptical
We now know that population I and II stars differ not only in their locations in the Galaxy, but also in their chemical composition, age, and orbital motions around the center of the Galaxy. Population I stars are found only in the disk and follow ______________ orbits around the galactic center.
nearly circular
The rotation curve of the Milky Way Galaxy shows what the the orbital speed of the farthest gas clouds from the galactic center (located in the outer regions of the Galaxy) ___________, indicating a great deal of mass beyond the Sun's orbit.
remains high
Our Milky Way Galaxy is what type of galaxy?
spiral
spiral
spiral-shaped region characterized by relatively dense interstellar material and young stars
The object in the center of most large galaxies that is so massive and compact that light cannot escape from it; 4.6 millions of Suns' worth of mass for the Milky Way galaxy.
supermassive black hole
halo
the outermost extent of our Galaxy (or another galaxy), containing a sparse distribution of stars and globular clusters in a more or less spherical distribution
