Q&A: Chandra Mission

Q:
The X-ray image of Orion Nebula seems to have a large cross in its center, as if it was formed by 4 quadrants. Why is that?

A:
The cross in the image is an instrumental artifact due to the arrangement of the CCD chips in the imaging array of the ACIS detector. See http://chandra.harvard.edu/about/science_instruments.html Some images do not show this effect because the image is entirely on one chip.