The Lockman Hole is a patch of the sky, lying roughly between the pointer stars of the Big
Dipper (centered at R.A. 10h 45m, Dec. +58° 00'), with an area of
15 square degrees, that is almost free from absorption by neutral hydrogen gas in the Galaxy. Having the minimum column density
of galactic hydrogen, it allows the most sensitive searches for extragalactic
objects and, for this reason, is one of the best studied sky areas across
a very wide range of wavelengths, from radio waves to gamma rays.
on the left is a deep X-ray Chandra image of the Lockman Hole. Virtually
each of these dots - with the red objects usually cooler than the
blue objects - represents a supermassive black hole. (Credit: ASA/CXC/U.
Wisconsin/A. Barger et al.)
The image on the right is a Digitized Sky Survey (DSS) of the Lockman
Hole in visible light. The field of view is slightly larger than the
Chandra image. (Credit: Pal.Obs. DSS)
AND INTERPLANETARY MATTER