This shining disc of a spiral galaxy is NGC 24, discovered by British-German astronomer William Herschel in 1785, is viewed here by the NASA/ESA Hubble Space Telescope. But there’s more to this picture than first meets the eye. Astronomers suspect that spiral galaxies like NGC 24 and our Milky Way are surrounded by, and contained within, extended haloes of mysterious ‘dark matter’. Most of NGC 24’s mass — a whopping 80% — is thought to be held within such a dark halo… Read more at http://www.spacetelescope.org/images/potw1639a/
