Project Overview

You will be given a list of galaxies that you will include in your description of Hubble's law. For each galaxy,you will need to find the luminosity distance and the radial velocity. You can find this information on the NASA/IPAC Extragalactic Database (NED). On NED, you will sarch by object name (first column, first row). The page of results for each object will come in an index. Click on the link for "Basic Data" to find the radial velocity:



The radial velocity shown in the example above is 3901 km/s. The "+/- 10 km/s" represents the error in the measurement, which we won't need to know for this project. Going back to the index, click on the link for "Quantities Derived from Redshift" to find the luminosity distance:



The luminosity distance in the example above is 51.1 Mpc (megaparsecs, with 1 Mpc = 1 million pc). These are the units you want to use: km/s for radial velocity, and Mpc for distance.

What you will be doing with this data is plotting it on a radial velocity vs. distance graph. (For instructions on how to plot using Excel, click on this link.) With the data plotted, you can find the equation for the line. The data should represent a straight line, which means that the equation will be y = mx, where y is the vertical axis (the radial velocity), x is the horizontal axis (the distance), and m is the slope of the line. If we call the slope H, then we find the equation v = Hd, which is known as Hubble's law. Your job will be to use the data plot to estimate the Hubble constant, H, which is the slope of the data plot.

What you will turn in will be a detailed report, with the following sections:

• Introduction: State the purpose of this report and give an outline for your calculation (how you are going to estimate Hubble's constant). Include an outline of the history of Hubble's law, which you will need to research on your own. For the history, make sure to include the year(s) when Hubble worked on the problem, the year that he published his results, what he was working on when he discovered Hubble's law, etc.
• Data: For this section, include a table with the radial velocity and distance listed for each of your galaxies that you have been assigned.
• Hubble's Law: Here, you want to include the graph of your data, as well as the equation for the line representing that here. This is where you'll estimate Hubble's constant and show that the data fits the equation v = Hd.
• Results and Conclusions: List, again, just the Hubble's constant as your result. You should talk about what Hubble's law means for the universe's evolution. The most impotant conclusion will be an estimation of the age of the universe, which you can make using Hubble's constant. How does your estimation of Hubble's constant match up with the accepted value of Hubble's constant?

Project Due Date: Friday, April 22

Student Data Sets