Sagittarius Dwarf Spheroidal Galaxy
The Sagittarius dwarf elliptical galaxy ( also SagDEG, Sagittarius Dwarf Elliptical Galaxy for ) is a small neighboring galaxy the Milky Way. At a distance of only 70,000 light-years from our solar system, so almost half the distance to the Magellanic Clouds, it is after the Canis Major dwarf galaxy, the second nearest galaxy outside the Milky Way.
This galaxy should not be confused with the 4.2 million light- years away in the Sagittarius dwarf irregular galaxy ( SagDIG for Sagittarius Dwarf Irregular Galaxy).
Distance and location
The Sagittarius dwarf galaxy is, like the other neighboring galaxies mentioned above, a satellite of the Milky Way and orbits the Milky Way center in a nearly polar orbit. Today's distance from the center of the Milky Way is about 50,000 light-years, the current position of the earth seen is close to the dense central part of the Milky Way. Accordingly, the apparent brightness of this dwarf galaxy is extremely weakened by interstellar extinction and it was therefore only discovered in 1994. For the next ten years, the Sagittarius dwarf galaxy was considered to be the nearest neighbor of the Milky Way, lost this, titled ' However, in 2003 at the above-mentioned Canis Major dwarf galaxy.
The trajectory which is assumed in the present state of research, suggests that the dwarf galaxy will move within the next 100 million years through the galactic plane; the future of this galaxy is therefore uncertain, as the tidal forces of the Milky Way and the interaction with the interstellar matter should cause a slow dissolution process.
Internal structure
The densest part of the Sagittarius dwarf galaxy has a diameter of about 10,000 light- years and taking in the sky corresponding to an area of about 8 degrees diameter a. This part corresponds to a typical elliptical dwarf galaxy, but are by the enormous tidal forces many members already removed from the core and spread out in a long strip along the orbit of the galaxy. Although this resolution process is confirmed both by numerical calculations and by direct observation, some researchers assume that the dissolution process progresses less rapidly than predict the bills. Reason for this assumption is that models for which the dwarf galaxy orbiting the Milky Way has about ten times, and according to the theory in this case, no such coherent dense core as should have observed. One possible cause of this coherence could be a large amount ( in such cases often approach drawn to explain ) dark matter in the center of the dwarf galaxy.
The approximately one billion stars, which contains the Sagittarius dwarf galaxy are, majority of the population II, that is, they are older and metal-poor and also the galaxy contains little interstellar matter, as is typical for dwarf elliptical galaxies. Both facts suggest that the galaxy is older. Moreover, it seems to those of the Large Magellanic Cloud to give a striking similarity between the stars. Then based hypotheses, according to which the Sagittarius dwarf galaxy was in earlier times associated with the Magellanic Clouds.
Companion
The Sagittarius dwarf galaxy has its own globular clusters, namely Messier 54 This bright globular clusters has been known for over 200 years and (apparently) much brighter than the galaxy, as it is not obscured by interstellar dust.