Well, here we are with another day done at the 233rd AAS meeting in Seattle. There were a lot of good sessions today and several great plenary presentations. I'm going to pick on one of the plenary sessions today dealing with X-ray astronomy.
But first, let's just remind everyone that we are here in Seattle, where to my experience of having been in this city for not more than 10-12 days in my entire life, it seems it has a Starbucks on every block and rain and clouds just about all the time. This is a bit of an exaggeration, but this night scene walking back from the last session shows rain wetted streets and my iPhone screenshot of the nighttime observing weather sort of supports my contention.
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| Seattle intersection between hotel and convention center (Source: Palmia Observatory) |
So, who scheduled an astronomy meeting in Seattle anyway? Next year the winter AAS meeting will be held in Hawaii. That will probably be a very popular meeting and maybe even Resident Astronomer Peggy will show up for that meeting!
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| Poor nighttime sky observing forecast during 233rd AAS in Seattle (Source: Palmia Observatory) |
Ok, ok, I know Seattle can have very clear weather, but not this week for sure. Anyway, the one plenary on the occasion of the20th year of successful operation of the Chandra X-ray Observatory and Dr. Ryan Hickox, Dartmouth University, was especially interesting.
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| Plenary Lecture: Twenty Years of Science with Chandra X-Ray Observatory (Source: Ryan Hickox, Dartmouth, at 233rd AAS Meeting) |
Why make X-ray observations? X-rays are higher frequency than visible light and they represent atomic transitions that occur within atoms are very high temperatures and therefore can indicate what process can be going on in astronomical objects.
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The three main areas where x-ray observations are important are outlined in this next slide from Professor Hickox's presentation. The nuclear reactions which go on in stars and generate high temperatures and x-rays. Matter that falls into a black hole will be so hot that x-rays can be used to identify some of the details. Finally in large scale structure studies the measurement of x-rays from high temperature gas can help trace the evolution of galaxies.
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| X-ray measurements probe three main astronomical topics of study (Source: Ryan Hickox, Dartmouth, at 233rd AAS Meeting) |
The angular resolution capability of X-ray telescopes is getting to be as good as optical telescope resolution. Checkout these two images. The first is from 1995 using the ROSAT telescope. I've lost track of what the object actually is called, but the main point is to compare the resolution possible in 1995 to the same object as seen by Chandra during the first years of operation.
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| Same object shown now with Chandra resolution (Source: Ryan Hickox, Dartmouth, at 233rd AAS Meeting) |
Now on to one of the very most important uses of x-ray observations is the tracking of the elements that are heated and excited and produce the x-rays. This next slide shows a X-ray image of Cassiopeia A and the associated x-ray spectra. Here it is important to differentiate between the energy of the x-ray photons and the number or amount or flux of x-ray photons. The detected energy tells much about what chemical element is being excited and at what temperature the element has to be in order to emit a photon of that energy.
My iPhone image of the slide is a little blurry when it comes to the elements listed in the spectra, but we can see peaks associated with Oxygen, Neon and Magnesium up to Silica. Then in decreasing amounts we see peaks associated with Sulfur, Argon, Calcium and finally Iron at the bottom right. So with the energy of the imaged photon and the number of photons we can track where these elements show up.
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| The X-ray energy indicates what element is present (Source: Ryan Hickox, Dartmouth, at 233rd AAS Meeting) |
This next slide does just that. It shows where the elements show up in the image of Cassiopeia A. Now this is very helpful in understanding the evolution of Cassiopeia A, which is a supernova remnant. So this heavy star, which was the progenitor was at the end of its life and had burned up all of its hydrogen fuel and had in turn generated all of these other elements. The star can't generate any more energy when iron is all that is left at the central core and so the star starts to collapse and the supernova explosion begins. To me, it is kind of interesting to see that even though the star was mostly iron in its core, we see the remnant has really pushed the iron very explosively away from the center and shows up at the outer edge of the remnant.
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Finally, one of the most interesting findings is of the collision between two hot gas clouds and two associated clouds of presumed dark matter. The hot gas, being made up of ordinary baryonic matter, interacts through processes other than gravity and so follows a different trajectory than does the dark matter clouds, which only interacts gravitationally. The normal matter clouds are hot and are seen in x-rays. The blue clumps represent the dark matter clouds. The dark matter cannot be seen, so how is the blue cloud in the image generated? The slide indicates the blue regions of the two colliding galaxies are found using gravitational lensing and then superimposed on the x-ray image.
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| X-ray analysis shows distinct regions of dark matter and normal matter in Bullet Cluster (Source: Ryan Hickox, Dartmouth, at 233rd AAS Meeting) |
Anyway, thanks to Professor Hickox and the entire Chandra team on 20 years of successful operation with a project lifetime of at least another 10 years!
Stay tuned for more from the 233rd AAS. Until next time,
Resident Astronomer George
If you are interested in things astronomical or in astrophysics and cosmology
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