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Q&A: Galaxies, Galaxy Clusters, AGN, and Quasars

Q:
In the recent Perseus image, as taken by Chandra, I noticed (after enhancement) scan lines that are not obvious in the original. Given scan lines are concurrent with a radial gradient, what are the chances for moiré-like artifacts to arise that mimic structures suggestive of "sound waves"?

A:
It's a valid question, to ask whether the structures could be artifacts. Here at the CXC we independently analyzed the images, and got the same results as the authors. We're not sure what you mean by "scan lines" but I cannot see how the so-called ripples could be artifacts. If you look carefully at the high resolution images of the 3-color X-ray image you can see several of the most prominent ripples in there, before enhancement. The enhancement just emphasizes the ripples by removing much of the radial gradient. In other words, ripples are seen in the enhanced image because ripples are in the original image.

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