Extreme Astrophotography

Tuesday, September 20th, 2005 at 10:55 AM by Juan

Many years ago, when I was a graduate student, I did one of my first ever observing runs at the Burrell Schmidt 24 inch telescope on Kitt Peak in Arizona. I was assisting Dr. Greg Aldering in a search for diffuse intergalactic light. Since that time, the National Optical Astronomy Observatories (NOAO), the folks in charge of many of the nations larger "national" telescopes, shut down the Burrell Schmidt as a cost-saving measure. Luckily, scientists don’t tend to throw away anything that is remotely useful, so the astronomers at Case Western Reserve University took over the Burrell Schmidt and refurbished it. The result is that this 70 year old telescope is still doing cutting edge science, in fact, science very similar to what I was doing 15 years ago, but with much more success.

(Click on image for full-size version.) The CWRU astronomer’s extremely deep image of the Virgo Cluster, revealing the strands of diffuse intergalactic starlight. The dark dots cover foreground stars which have been removed from the image.

(Click on image for full-size version.) A more traditional image of the Virgo Cluster taken from the Palomar Sky Survey.[1] This image goes about 1 million times fainter than the human eye can see and yet it is clear the CWRU folks went considerably deeper when you compare this image to theirs.

One of the interesting challenges in astronomy is looking for very low surface brightness phenomena, where the amount of light you are looking for is less than the amount of light generated by chemical processes in the Earth’s atmosphere. It may surprise you to learn that astronomers can detect diffuse light fainter than the night sky, it is just a very tricky thing to do. If, for example, you wanted to detect faint diffuse galaxy light 1% as bright as the night sky, you would expose your CCD camera for a very long time (actually, you would take many shorter exposures and add them up, to avoid artifacts due to cosmic ray strikes on your camera). You would expect the region with the diffuse light to be 1% brighter than the regions nearby (in the same picture) which capture nothing but night sky. So say you get 100 counts in every pixel of you camera in the areas with nothing but night sky in them. You would expect 101 counts in the regions with the extra diffuse light. This would be very hard to see by eye, but wonderfully, since you know EVERY pixel in the camera has 100 counts due to the night sky, you can simply ‘delete’ the night sky by deleting 100 counts from every pixel in your image. And thus, PRESTO, you can see the diffuse light. Of course, in practice this is a bit tricky. That’s why the following news astounded me…

Dr. Chris Mihos, an astronomer at Case Western Reserve University, and his collaborators have managed to produce a wide field image of the Virgo Cluster, a crowded group of about two thousand galaxies, that goes "nearly 1000 times fainter than the night sky", a very impressive achievement.^[2]
And for that effort, he obtained a really amazing image showing the stellar flotsam and jetsam of material stripped from the galaxies in the crowded Virgo Cluster. Furthermore, by comparing the distribution of that faint starlight today with computer simulations of the evolution of the Virgo cluster over the last 10 billion years, they can get a better understanding of how galaxies evolve in these crowded environments. Plus, the picture is spectacular!

Posted in Astronomy News, Outreach

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