Файл:Caldwell 23 - 2.jpg

Astronomers used Hubble’s observations of Caldwell 23 to learn more about the structure and evolution of spiral galaxies. One of their findings helped identify the source of Caldwell 23’s galactic “halo.” The halo surrounds the galaxy and primarily contains old stars, some of which are grouped together in large, sphere-shaped collections called globular clusters. The source of this halo material has been unclear, since theoretically it could either originate in the galaxy or be gravitationally pulled in from the area surrounding the galaxy. Scientists using Hubble found that Caldwell 23’s halo is similar in composition to other material in the galaxy, which suggests that the halo material was expelled from within the galaxy.

This Hubble image shows wispy tendrils of dust and gas branching off from the plane of the galaxy into the halo. Astronomers believe these structures formed as material was ejected outward by supernovae or intense star formation activity. When massive stars light up at birth or explode at death, they produce powerful winds that can blow dust and gas over hundreds of light-years of space.

Caldwell 23 was discovered by astronomer William Herschel in October 1784. The galaxy has a magnitude of 10, so use a telescope to see it, away from any sources of light pollution. Under ideal conditions you can make out the galaxy’s central dark lane. Autumn night skies in the Northern Hemisphere will provide the best view. In the Southern Hemisphere, look for Caldwell 23 in the springtime.

For more information about Hubble’s observations of Caldwell 23, see:

www.spacetelescope.org/images/potw1220a/

hubblesite.org/contents/news-releases/1999/news-1999-10.html

Credit: ESA/Hubble & NASA; Acknowledgement: Nick Rose

For Hubble's Caldwell catalog site and information on how to find these objects in the night sky, visit:

www.nasa.gov/content/goddard/hubble-s-caldwell-catalog