Image Credit & Copyright: R. Jay GaBany, Cosmotography (http://www.cosmotography.com)
NGC 891 (also known as UGC 1831 and Caldwell 23) is a spiral galaxy about 100,000 light-years in diameter with an H II nucleus and a mass of about 320 billion Sun masses. It is located 27 million light-years away in the constellation Andromeda and is a member of the NGC 1023 group of galaxies in the Local Supercluster (or Virgo Supercluster). In August 1986 Supernova SN 1986J was discovered.
The edge-on galaxy reveals its plane of dust and interstellar gas, in the middle intersected by areas with dark, obscuring dust. The bulge and the disk are surrounded by a flat and thick cocoon-like stellar structure. One can also also distinguish young blue star clusters and characteristic pink red starforming areas.
NGC 891 appeared previously to be very similar to our own Milky Way Galaxy: a spiral galaxy seen edge-on with a flat, thin, galactic disk and a central bulge. However, recent high-resolution images of NGC 891 show unusual filamentary patterns of gas and dust, that extend hundreds of light-years above and below the center line.
Astronomers believe these filaments are the result of the ejection of material due to supernovae or intense stellar formation activity. Stars cause powerful winds by lighting up when they are born, or exploding when they die, that can blow dust and gas over hundreds of light-years in space.
Investigations in infrared give rise to suspects that NGC 891 has a bar. This bar, if it exists, cannot be seen, as it is edge-on from our perspective. The bar hypothesis is also supported by the fact that the billions of stars orbiting the center appear to be moving too fast to just be travelling in circles.