Caption: All-sky map of the "high-velocity clouds". Many of these clouds are high above the plane of the Milky Way, although for the most part they remain
enigmatic. The one outlined, and possibly others too, is now known to have low
heavy element content and to be raining down onto the Milky Way disk, seeding
it with the stuff of stars. Identifying this infalling gas helps in solving a
long-standing mystery of galactic evolution by revealing a source of the
low-metallicity gas required to explain the observed chemical composition of
stars near the Sun. This discovery is based on combination of data from the
Hubble Space Telescope, three radio telescopes (at Effelsberg in Germany, and
Dwingeloo and Westerbork in the Netherlands), the William Herschel Telescope
on the island of La Palma and the Wisconsin H-alpha Mapper at NOAO's Kitt Peak
Image composite by: Ingrid Kallick of Possible Designs, Madison Wisconsin.
The background Milky Way image is a drawing made at Lund Observatory.
High-velocity clouds are from the survey done at Dwingeloo Observatory
(Hulsbosch & Wakker 1988).
High Resolution JPEG 300 DPI