Q&A: Milky Way Galaxy
How far are we from the galactic plane and the center of the Galaxy?
The composite image at left shows Chandra observations of the galactic plane (inset) in relation to the familiar optical view of the Milky Way. The Chandra data focus on a tiny region in the constellation Scutum. Chandra's image marks the deepest X-ray look at the "zone of avoidance" -- a region of space behind which no optical observation has ever been taken because thick clouds of dust and gas in the spiral arms of the Milky Way block visible radiation. X-rays, along with certain radio and infrared wavelengths, can penetrate this barrier. The diffuse blue emission is due to hot (ten million degree Celsius) gas concentrated along the plane of the Galaxy.
Most of the pink and red objects sources in this image are believed to be active stars in our Milky Way galaxy. The blue objects, referred to as "hard" sources because they emit more energetic X-rays, are considered to be distant galaxies. Because astronomers were able to identify these objects as being well beyond the galactic plane, they were able to determine that the X-ray glow from the galactic plane comes not from individual sources, but from the hot diffuse gas.