| Term: | Local Group |
| Definition: |
A small galaxy cluster of about 50 galaxies to which our Milky Way galaxy belongs. The Local Group occupies a volume of space nearly 10 million light-years across centered somewhere between the Andromeda Galaxy (M31) and the Milky Way, which are the dominant galaxies of the group; Andromeda being the principal member. Both of these galaxies exhibit spiral structures, and each is attended by a large family of satellite dwarf galaxies. The Local Group also includes a third spiral galaxy known as Triangulum (M33), which is bound to Andromeda. The remaining members span a range of Hubble classification types from dwarf spheroidal to Irr to Sb and Sc and cover a factor of 10 in metallicity. The total mass of the Local Group is estimated to be about 2 x 10^12 solar masses, although this value is still uncertain to within a factor of about 2. The velocities of the individual galaxies of the Local Group are not particularly high. Therefore no member is believed to be able to escape the group, which is thus considered to be gravitationally bound. Another remarkable member of the Group is IC 10. |