(Left) HST ACS image of 1/200 of the full GOODS fields shows three X-ray sources (circled) and many other galaxies. (Right) Combined HST-Spitzer IRAC image of the same region. The two "hard" X-ray sources (yellow circles, indicating sources detected only at the shortest X-ray wavelengths) are very faint in the visible but much more luminous in the infrared, exactly as expected if the accreting black hole is hidden behind a dusty screen.

Credit: NASA, ESA, A. M. Koekemoer (STScI), M. Dickinson (NOAO) and The GOODS Team