Quasars Teacher Notes
Quasars are the most distant and luminous objects ever observed. In less than three years of operation, the SDSS discovered 26 of the 30 most distant quasars ever seen. Students can see some of these quasars in this project.
Quasars are the active nuclei of extremely distant galaxies. They are believed to be powered by black holes with masses of millions or even billions times the mass of our Sun.
Quasars are so far away that their light takes billions of years to reach us – therefore, we see them as they appeared billions of years ago. When we look at a quasar, we are essentially looking backward in time billions of years.
The Quasars project is fairly difficult, and it assumes a lot of background knowledge in astronomy. Students must know how to identify spectral lines, how to qualitatively relate redshift to distance, and how to create color-color diagrams. We recommend that students complete the Hubble diagram project, the Spectral Types project, and the Colors project before tackling the Quasars project.
For a shorter version of the project, you may wish to omit the sections on querying the SDSS database. These sections are rather advanced, and students will be analyzing data for 1000 quasars at once. If you students are not well versed in Excel or some other spreadsheet program, you would probably be better off doing the shorter project.
To do the shorter version of the project, end with the “Power Source of Quasars” page.
For more information about quasars or about the history of their discovery, read the About Astronomy section of SkyServer, or one of the following refernces:
Black Holes, Quasars, and the Universe, by Harry L. Shipman
First Light, by Richard Preston
Our Evolving Universe, by Malcom S. Longair
The Quasars FAQ, by John Simonetti
“The Rise and Fall of Quasars,” by G. Mark Voit, Sky and Telescope, May 1999
By the end of this project, students should be able to:
- Know that quasars were discovered due to strong radio emissions that some of them give off.
- Understand that redshift of light is caused by an object moving away from us very rapidly.
- Recognize the movement of spectral lines to the red as redshift increases.
- Correlate red shift to velocity.
- Recognize quasars as extremely distant objects that are only seen at high redshifts.
- Know that quasars do not currently exist in the universe. The youngest quasars died out hundreds of millions of years ago. Scientists do not know why.
- Know that quasars must emit tremendous amounts of energy for them to be visible at such great distances.
- Realize that the power source of quasars is very small, about the size of our solar system.
- Know that quasars are believed to be powered by matter falling into a supermassive black hole at the center of early galaxies.
- Compare visual images and radio images of quasars to see if they are radio loud or radio quiet.
- Run a simple query of a database and import the results into a spreadsheet program.
- Create color-color diagrams and color-redshift diagrams for quasars.
This project assumes a fair amount of background from other SkyServer projects. Students should be familiar with the concept of redshift and that the universe is expanding. They also need to know that due to the time it takes light to reach us, we are looking into the past when we see objects hundreds of millions or even billions of light years away. Students can learn these concepts in the Hubble diagram project.
To compare the star, galaxy, and quasar spectra, students should know how to identify absorption and emission lines in spectra. They can learn how to identify these lines in the Spectral Types project.
For the final project, students will need to be familiar with color-color diagrams to they study the colors of quasars. They can practice making these diagrams in the Colors project. In addition, spreadsheet skills will be important as they tackle the final challenge.
The first part of the project introduces students to quasars in the way astronomers first discovered them: by looking at objects with strong radio emissions. In the first section, students look at data from the VLA FIRST SURVEY, a radio counterpart to the SDSS. VLA FIRST will look at 10,000 square degrees of sky, including areas that SDSS does. Objects that emit radio waves are marked in the SDSS database. Students will look at four different quasars and their radio emissions.
Next, students will look at the spectra of quasars. They will compare the spectra of quasars to those of normal stars and galaxies. Students will also see how the emission lines of quasars change as their redshifts increase.
Students will then learn about the power source of quasars. From all available evidence, the most likely candidate is a supermassive black hole at the center of a distant galaxy. As the black hole pulls gas into it, the gas is heated up to millions of degrees, emitting vast amounts of energy.
In the last, and most challenging, part of the project, students use SkyServer’s SQL Query tool to obtain data for 1000 quasars. They can then use this data to make color-color or color-redshift diagrams.
Questions and Exercises
Questions are designed to get students thinking about the way scientists work. Exercises are designed to get students to explore SkyServer data. For answers to all questions and exercises, email us at email@example.com.
Students should be evaluated based on their written answers to the questions and exercises. You may use our sample scoring rubric or develop your own. If you use our scoring rubric, print out a copy for each student and attach it when you return his or her work.
For specific information on any part of the project, click Next.