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Supernovae are the violent explosions of stars occurring at the end of their lives. On average, one supernova goes off every 50 years or so in our Galaxy. The enormous explosion from these stars blasts material out into the surroundings at very high speeds, sweeping up the surrounding gas into a giant bubble. This is known as a supernova remnant. The shell (or bubble) shines at many different wavelengths, and is very bright in the X-ray because the material from the explosion is very hot. Different things are happening in different wavelengths; when we observe in, say the X-ray, we are looking at the parts of the shell that are much hotter than the areas shining in the visible.
Supernovae release more energy in a single instant than the Sun will produce in its whole lifetime! If the nearest massive star, Betelgeuse, in the constellation Orion, were to go supernova it would (for a short time) be brighter than the full moon. Here we will look at the historical ancient cosmic explosion called Cassioepeia A, the remnant left behind after a star exploded 320 years ago which lies at a distance of 11,000 light years away. Cassiopeia A (or Cas A as it's often called), is the brightest radio source in the sky!
For this activity you will make color composite images by combining images from different wavelengths. This can be done using Photoshop. You will be creating your own multi-wavelength (color) images of the Cas A supernova remnant taken with the Faulkes Telescope North and with an X-ray image from the Chandra X-ray telescope. To do this download the Cas A dataset which includes three images of Cas A taken with LCO using B, OIII and R and the X-ray image. The data set also includes the Hubble Space Telescope image of Cas A. Firstly, we will compare the optical and X-ray images to see how or if they differ.
> Download the data files
1. In DS9, open one of your LCO images of Cas A
File > Open...
Adjust the scale and zoom so that you can see Cas A
e.g. Scale > 99%
Zoom > To fit2. In DS9, open another frame and load the X-ray image into this frame
Frame > New Frame > File > Open
Again, adjust the scale and zoom so Cas A is visible
3. Tile the images in DS9 so that both are visible
Frame > Tile Frames
Adjust the viewing window so that you can fully see the two images
4. Now describe the different features in the visible (optical) and X-ray images in the corresponding ovals below. In the overlapping part, describe what the images have in common.
1. Follow the instructions in the How-to article: How to make color astronomical images with Photoshop and create a colour image of Cas A using the B, OIII and R images taken with Faulkes Telescope North (The OIII filter is in the green part of the electromagnetic spectrum, so can be used as the green image for this activity. You could also use Halpha which is in the red part of the electromagnetic spectrum, so can be used as the red image). This is your LCO three-color visible image.
2. Once you have made your color image, add the X-ray image as a separate layer. You can colour the X-ray image any color you like, but when you add it on top of your LCO visible image, ensure you change it’s mode to ‘Screen’ (as you did previously with the color images).
You should now have a multi-wavelength image consisting of optical and X-ray data, and the differences which you noted in Part 1 should be even clearer in this final image.
Download the data set at the bottom of this page. You will use DS9 and Photoshop for this activity.