Galaxy group

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The local group of galaxies in the vicinity of the Milky Way.

A galaxy group is a smaller collection of galaxies with fewer than 50 members in a volume with a diameter of up to 1.5  M pc (about five million light years ). Typical values ​​for their masses are M ≈ 3 × 10 13  M ☉ ; the speeds of its members vary by about 150 km / s.

In contrast, one speaks of galaxy clusters with N ≥ 50 members, diameters D ≥ 1.5 Mpc and masses M ≥ 3 × 10 14  M ☉ .

Local group

The galaxies group to which the Milky Way is called the (English. Local Group Local Group ) . About 35 galaxies belong to it, which are within a distance of ≈ 1 Mpc from our galaxy.

The Milky Way, Andromeda (M31) and the Triangle Nebula (M33) are the three spiral galaxies of the Local Group and their most luminous members. The Andromeda Galaxy is about 770 kpc from us.

The next-most luminous member of the Local Group is the Large Magellanic Cloud (Engl. Large Magellanic Cloud , LMC), which together with the Small Magellanic Cloud (Engl. Small Magellanic Cloud kpc, SMC) at a distance of ≈ 50 (or ≈ 60 kpc for the SMC) moved around the Milky Way. Both are satellite galaxies of the Milky Way and, like about 11 other members of the local group, belong to the class of irregular galaxies . The other members of the Local Group are dwarf galaxies .

Close groups

The area around the local group up to a distance of around 20 million ly. The plane drawn is the equatorial plane of the earth, the two arrows indicate the direction to the center of the local supercluster , the Virgo galaxy cluster , or to the somewhat smaller Fornax galaxy cluster , which are each about 60 million ly away.

The most important galaxy groups in the vicinity of the local group are:

  • The Maffei group , named after the discoverer of the two largest galaxies in this group. From our point of view, this group at a distance of 6 to 12 million light years is almost completely covered by the Milky Way disk. Despite being the closest neighbor group (it was considered part of the Local Group even a few years ago), it wasn't discovered until late in the twentieth century. The only brighter galaxy in this group that does not appear extremely darkened by interstellar extinction is IC 342 . The group lies in the constellations Cassiopeia and Giraffe .
  • The Sculptor group , named after the constellation Sculptor , in which the brightest members of the group reside. This group is about 10 million light years away and contains the Sculptor Galaxy (NGC 253), the brightest galaxy outside the Local Group, which can be seen in the southern hemisphere.
  • The M81 group , which is only a little further away than the Sculptor group and with Bodes Galaxie (M 81) contains the brightest galaxy outside of the local group.
  • The M83 or NGC 5128 group , which is named after the brightest member galaxies , the southern firewheel galaxy (M 83) and Centaurus A (NGC 5128). The group can be found in the southern sky in the constellations water snake and centaur and is 12 to 17 million light years away.
  • The Canes Venatici I or M94 group in the constellation Hounds . The group is 13 to 18 million light years away; its brightest member is the spiral galaxy M 94 .

Web links

Commons : Galaxy groups  - collection of pictures, videos and audio files

Individual evidence

  1. ^ Springer-Verlag, Berlin, Heidelberg: Galaxy clusters and groups of galaxies . In: Introduction to Extragalactic Astronomy and Cosmology . 2008. doi : 10.1007 / 3-540-30589-0_6 .
  2. ↑ galaxy. In: Andreas Müller , Lexicon of Astrophysics. August 2007, accessed July 29, 2019 .