University of Michigan - Department of Astronomy

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Stellar Evolution

Whirl on, giant clouds of gas; may you reach a threshold mass.
Protostars and blobs and dots, form within your glowing knots;
Whirl on, giant clouds of gas; may you reach a threshold mass.

--Pietro Calogero (a new verse for Twinkle Twinkle Little Star)



Stars spend 90% of their lifetime on the Main Sequence, but in the last 10% of their lives, their life tracks take them to other parts of the Hertzsprung-Russell Diagram. The stars change dramatically in temperature, luminosity, and size. They also produce some fascinating end-products in these late evolutionary stages.

Theories of stellar evolution were originally founded on  a few optical observations and some physics and chemistry.  These  initial models were difficult to confirm when they were first  developed.  However, modern observations, like the discovery of a supernova in the Large  Magellanic cloud in 1987, have advanced our understanding of  stellar evolution into a true scientific theory. Our understanding comes from a mixture of images at many different wavelengths as well as data, such as light curves. The Hertzsprung-Russell (H-R) diagram is a useful tool for organizing our information. We can trace the changes in luminosity and surface temperature over time on an H-R diagram.  In this lab you will look at a number of pictures, including multi-wavelength images and illustrations.  Your goal will be to identify the images and put them in place on an H-R diagram.

You can get a pdf with the images here

Part 1: Identifying the Images

Begin by identifying each of the pictures. Note what the object is in the description column of table 1 in the row with that picture's number. If the object is specifically a stage in a middle (2MSun) or high (~50MSun) mass star's evolution, make a note of that: e.g. your description might start with "middle-mass main sequence star". Add any other notes to the description that will help you put the objects in order latter. Note there are objects that fit any mass, but none that are specific to the evolution of a low-mass star.

Once you know what the objects are, determine what their luminosity and temperature are. Record these in table 1, in solar luminosities and thousands of Kelvins (kilo-Kelvins for short). If the object has a range of values, record the average value rather than the range.

Table 1: The Images
L (LSun)
T (kK)

Part 2: Stellar Evolution

Sort out all the images that are needed to plot the evolution of a middle mass star. Determine the age of the object in each image. Record the image number and age in table 2 under the Middle Mass section.

Do the same thing for the evolution of a high mass star, but regord the number and age under the High Mass section. Note since some of the images apply to both middle and high mass evolution, they will appear in both sections.

Table 2: Evolution Sequence
Middle Mass High Mass
Number Age Number Age

Part 3: The H-R Diagram

There are two H-R diagrams at the end with the Main sequence marked. Label one of the "Medium Mass" and sketch IN PENCIL the life path from formation to death of a middle mass star on it. Label the other one "High Mass" and sketch the life path of a high mass star on it.

Determine where each of the pictures falls on your two graphs, and mark the position. Check to make sure the image not only sits somewhere on the life path, but that it also matches reasonably well with the luminosity and temperature from table 1. Adjust your life path where approproate. Mark the position of each image, and label it with the number from the image.


Last modified: 9/15/06

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