Education Activities To Accompany Chandra Data Analysis Software M31 & Coma
Big, Bigger, Biggest
Activity 1: Let's look at M31 in x-rays and visible light
A) Open DS9. Connect to the Chandra-Ed Archive server through the virtual observatory. Load the M31 Chandra image. Go to: Color > bb, Scale > log. What you now see is a bunch of point-like x-ray sources. These are most likely binary star systems emitting x-rays from the nucleus of M31.(The dark "crosses" you see are part of the satellite hardware, and are spaces between the x-ray sensitive chips that you can clearly see in the image.) Now, let's see exactly where in the sky these sources are. Go to:
Frame > tiles frames
Analysis > DSS server > retrieve. This will allow you to place, side-by-side with your x-ray image, the visible light in that region of the sky, seen through a large telescope. Set:
Scale > sqrt for the best image detail.
Here is the nucleus of M31, our closest spiral galaxy neighbor, a mere 2 million light years away. Imagine, light that you see coming from M31 on a clear autumn evening anywhere in the northern hemisphere (yes, you can see it with your naked eye if you know where to look), left the galaxy long before modern humans (homo sapiens) ever walked the Earth. See the activities for 3C273 to determine the size of M31.
Now we can do something really neat. Go to: Frames > match frames > WCS and Frame > lock crosshairs > WCS. Then Edit > crosshairs.
Now, crosshairs will appear on both images, and you can "grab" either crosshair by left clicking and holding down the mouse button on the intersection of the two lines; now you can roam around the image and the two crosshairs will track together through space. So you can see exactly where in the galaxy each of the x-ray sources are coming from. Notice that almost all of them seem to be quite faint and nothing special in visible light. But let's see how much x-ray energy is coming out of these bright, "point" sources.
B) Using an analysis similar to that described in our discussion of 3C273, verify that the luminosity of the source near physical pixel (4185, 4081) is about 1037 ergs/sec. So these innocuous appearing objects are radiating about 10,000 times the total light output of our Sun, and about 10 billion times more than our Sun's x-ray production!
C) Can you think of another way to verify the luminosity of this source? (Hint: use the pixel table in DS9, plus the total length of the observation, which can be obtained by going to File > Display FITS header.)
