In this map of a celestial hemisphere, the colors reflect the wavelengths of X-rays . Hot gas haloes surrounding galaxy clusters have broad-band emissions (white), as do black holes (white dots); diffuse emissions have long wavelengths (red); and in the central regions of the Milky Way, dust blocks longer-wavelength emissions . As its name suggests, dark matter doesn’t emit light, absorb light, or interact with normal matter at all .