July 29, 2013
NGC 3953, a spiral galaxy in Ursa Major
Image Credit: Tom and Gail Haynes/Adam Block/Mount Lemmon SkyCenter/University of Arizona (http://skycenter.arizona.edu/gallery)
NGC 3953 is a barred spiral galaxy of about 111,400 light-years across, located some 56 million light-years away from Earth in the northern constellation of Ursa Major (the Great Bear), while it is receding from us at approximately 1052 kilometers per second. NGC 3953 is a member of the M109 Group, that may contain over 50 galaxies within the constellation of Ursa Major.
It has a small, very bright active nucleus, and an inner ring structure just beyond the nucleus. The tightly wound arms are laced with dark dust lanes and several blue star clusters with young, hot stars.
Two supernovae have been observed within NGC 3953: on August 12th 2001 a Type Ia supernova called SN 2001dp, and on April 10th 2006 a Type II supernova called SN 2006bp.
A supernova is a phenomenon in which a star explodes in the final phase of its life. There are two types: Type I and Type II. The Type I does not show hydrogen in the spectra. The Type I category is sub-divided into Type Ia, Type Ib and Type Ic supernovae. Among these, Type Ia are explosions of white dwarf stars. The other group, Type II, are explosions of massive stars (initially more than 8 times the mass of the Sun). The Type II supernovae do show hydrogen in their spectra.