Tons of space issues # 2? 11. Why do we call dark matter "dark"?
a. It emits light of other wavelengths, but not at visible wavelengths.
b. We can not detect the type of radiation it emits.
C. It emits no or very little radiation of any wavelength and does not reflect light.
d. It blocks the light from stars in a galaxy.
12. What evidence suggests that the Milky Way contains dark matter?
a. We observe clouds of atomic hydrogen near the galactic center orbiting the galaxy at speeds unexpected speeds higher than they would if they feel the gravitational pull of objects we can see.
b. We see many ways of dark material blocking the light from stars behind them along the strip of the Milky Way.
C. We see many dark voids between the stars in the halo of the Milky Way.
d. When we observe in different wavelengths, such as infrared or radio, we see objects that are not included in the observations in visible light.
e. When you look at the galactic center, we are able to observe a black hole which is composed of dark matter.
13. The distribution of dark matter in a spiral galaxy is
a. approximately spherical and about the same size as the halo of galaxies.
b. After approximately spherical and about ten of the halo size of galaxies.
C. flattened into a disk and about the same size as the stellar disk.
d. flattened into a disk, but about ten times larger than the stellar disk.
e. mainly concentrated in the spiral arms.
14. How to determine the amount of dark matter in elliptical galaxies?
a. We measure the orbital speeds of gas clouds in star formation in the outer parts of the galaxy.
b. We measure the velocities of stars at different radii from the galactic center and determine how much mass is inside the orbit.
C. We count the number of stars in the galaxy and determine its volume, so that we can calculate the density of the galaxy.
d. We are looking for dark lanes of dust and black holes within the galaxy.
e. We measure the speed of rotation of the galaxy as a whole.
15. Which of the following statements is not evidence of dark matter?
a. rotation curves of spiral galaxies flat
b. enlargement of the absorption lines in the spectrum of an elliptical galaxy of
C. X-ray observations of hot gas in galaxy clusters
d. gravitational lensing around clusters of galaxies
e. the fact that the universe is expanding
16. Dark energy
a. may be the missing piece that stops the cosmic expansion, it causes the collapse again
b. is driving the expansion of the universe at an accelerating pace.
C. is known as a common form of energy created in particle accelerator laboratories.
d. None of these answers is correct.
17. A world that is more than the critical density, which has a closed geometry will
a. continue to expand indefinitely, but it will always be on the verge of collapse.
b. continue to grow indefinitely at an accelerated pace.
C. Reduce to a certain point in the future.
d. install in a static state, where the expansion stops, but does not collapse.
e. None of these answers.
18. Methods for detecting the composition of dark matter
a. involve attempts to detect their macho by gravitational lensing of more distant starlight.
b. attempts at direct detection of WIMPs using germanium crystals cold.
C. attempts to involve indirect detection of high energy neutrinos created by the annihilation of WIMPS within massive bodies like the Sun.
d. show that only a very small perc.
Posted on May 30, 2010.
