Why can we not measure the mass of elliptical galaxies using the 21-cm line of hydrogen gas?
A) All elliptical galaxies are too far away for us to detect the 21-cm line.
B) Supermassive black holes in the center of elliptical galaxies disturb measurements of the 21-cm line.
C) The disorderly motion of the material in elliptical galaxies prevents us from measuring different velocities at different sides of the galaxy.
D) Elliptical galaxies have little gas, so do not have strong 21-cm line emission.
D
You might also like to view...
A wheel (radius = 12 cm) is mounted on a frictionless, horizontal axle that is perpendicular to the wheel and passes through the center of mass of the wheel. A light cord wrapped around the wheel supports a 0.40-kg object. If released from rest with the string taut, the object is observed to fall with a downward acceleration of 3.0 m/s2 . What is the rotational inertia (of the wheel) about the
given axle? a. 0.023 kg/m2 b. 0.013 kg/m2 c. 0.020 kg/m2 d. 0.016 kg/m2 e. 0.035 kg/m2
The planets in the solar system
A) revolve around the Sun in the same direction B) orbit around the Sun in nearly the same plane C) have nearly circular orbits D) all of these are true
An alpha particle is a nucleus of helium. It has twice the charge and four times the mass of the proton. When they were very far away from each other,
but headed toward directly each other, a proton and an alpha particle each had an initial speed of 0.0030c, where c is the speed of light. What is their distance of closest approach? Hint: There are two conserved quantities. Make use of both of them. (c = 3.00 × 108 m/s, k = 1/4??0 = 8.99 × 109 N ? m2/C2, e = 1.60 × 10-19 C, mproton = 1.67 x 10-27 kg) A) 3.3 × 10-13 m B) 2.6 × 10-13 m C) 2.1 × 10-13 m D) 2.9 × 10-13 m
If you need 10 moles of sucrose, how many liters of a 4.0 molar solution would you need?
A) 2.5 L B) 0.25 L C) 25 L D) 10. L E) none of the above