21.Molecular clouds can be observedA.using infrared telescopes to detect ionized : 1777238
21.Molecular clouds can be observed
A.using infrared telescopes to detect ionized gas in the clouds.
B.using x-ray telescope to observe the x-ray radiation from the molecules in the cloud.
C.using radio telescopes to observe the CO emission from the clouds.
D.by looking for blue wispy regions near star clusters.
E.by looking for the 21-cm radiation from hydrogen.
22.The main sequence has a limit at the lower end because
A.low mass stars form from the interstellar medium very rarely.
B.low mass objects are composed primarily of solids, not gases.
C.pressure does not depend on temperature in degenerate matter.
D.the lower limit represents when the radius of the star would be zero.
E.there is a minimum temperature for hydrogen nuclear fusion (the definition of a star).
23.There is a main sequence mass-luminosity relation because
A.helium fusion produces carbon.
B.stars expand when they become giants.
C.more massive stars support their larger weight by making more energy.
D.the helium flash occurs in degenerate matter.
E.all stars on the main sequence have about the same radius.
24.Due to the dust in the interstellar medium, a distant star will appear to an observer on Earth to be
A.brighter and cooler than it really is.
B.brighter and hotter than it really is.
C.fainter and cooler than it really is.
D.fainter and hotter than it really is.
E.unchanged in brightness or apparent color.
25.The lowest mass object that can initiate thermonuclear fusion of hydrogen has a mass of about
A.1 solar masses
B.80 solar masses
C.8 solar masses
D.0.08 solar masses
E.0.001 solar masses
26.Stars with masses less than ____ produce most of their energy via the proton-proton chain.
A.0.01 solar masses
B.0.1 solar masses
C.1.1 solar masses
D.11 solar masses
E.110 solar masses
27.The creation of ____ require(s) that a young hot star (T 25,000 K) be relatively nearby.
D.The cool gas of the interstellar medium
E.21 cm radiation
28.The extinction of starlight due to the interstellar medium
is the greatest in the ultraviolet.
is the greatest in the infrared.
is caused by ionized hydrogen.
is caused by dust particles.
A.I & III
B.II & III
C.I & IV
D.II & IV
29.____ are small dark nebulae about 1 light-year in diameter that contain 10 to 1,000 solar masses.
30.Absorption lines due to the interstellar medium indicate that some components of the interstellar medium are cold and of a very low density because
A.the lines are blue shifted.
B.the lines are red shifted.
C.the lines are extremely broad.
D.the lines are extremely narrow.
E.the lines are much darker than the stellar lines.