How does the rotation curve method differ from the analysis of binary stars?
What will be an ideal response?
Although there are a few ways to estimate the mass of a galaxy, the most direct measurement uses Kepler's third law of planetary motion. We used this method in an earlier chapter to find the masses of binary stars. If astronomers can measure the radius of a galaxy and the velocity with which it rotates, they can easily find the orbital periods of the stars as they orbit the galaxy. Then they can use Newton's version of Kepler's third law to calculate the mass of the galaxy. The most accurate of these studies involve observing the rotation of the galaxy at different distances from its center and drawing a graph called the rotation curve of the galaxy. Using such a graph to find the mass of the galaxy is called the rotation curve method. It is the most accurate way to find the mass, but it works only for the nearer galaxies, whose rotation curves can be observed. More distant galaxies appear so small astronomers cannot measure the radial velocity at different points across the galaxy.
You might also like to view...
The walls of an ice chest are made of 2.00 cm thick styrofoam with a thermal conductivity 0.0300 W/m?K
The total surface area of the ice chest is 1.20 m2. If 4.00 kg of ice at 0.00°C are placed in the chest and the temperature outside the chest is 20.0°C, how long does it take the ice to melt? Remember that the latent heat of fusion of water is 79.6 cal/g. A) 4.22 hours B) 22.1 hours C) 17.6 hours D) 1.33 days E) 10.3 hours
Which of the following describes a primary role of global circulation cells in a planet's atmosphere?
A) They transport heat from the equator toward the poles. B) They create severe weather such as thunderstorms. C) They cause air to be diverted into hurricane-like swirls. D) They keep the poles cold enough to have polar caps.
What is the radius of curvature of the path of a 3.0-keV proton in a perpendicular magnetic field of magnitude 0.80 T?
a. 9.9 mm b. 1.1 cm c. 1.3 cm d. 1.4 cm e. 7.6 mm
Thermoset polymers _________ melt when heated to a high temperature in the presence of oxygen.
Fill in the blank(s) with the appropriate word(s).