Sagittarius Dwarf Spheroidal Galaxy
| Sagittarius Dwarf Spheroidal Galaxy | |
|---|---|
| Observation data (J2000 epoch) | |
| Constellation | Sagittarius |
| Right ascension | 18h 55m 19.5s |
| Declination | −30° 32′ 43″ |
| Redshift | 140 ± ? km/s |
| Distance | 65 ± 7 kly (20 ± 2 kpc) |
| Apparent magnitude (V) | 4.5 |
| Characteristics | |
| Type | dSph(t) |
| Apparent size (V) | 450′.0 × 216′.0 |
| Notable features | Heading for a collision with the Milky Way |
| Other designations | |
| Sag DEG, Sgr dSph, Sagittarius Dwarf Spheroidal, Sgr I Dwarf | |
The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy (Sgr dE or Sag DEG), is an elliptical loop-shaped satellite galaxy of the Milky Way. In the Catalogue of Named Galaxies, it is called Divulsus Sagittarii, or the torn-in-pieces galaxy. It consists of four globular clusters, the main cluster having been discovered in 1994. Sgr dSph is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth, travelling in a polar orbit (i.e. an orbit passing over the Milky Way’s galactic poles) at a distance of about 50,000 light-years from the core of the Milky Way (about 1/3 the distance of the Large Magellanic Cloud). In its looping, spiraling path, it has passed through the plane of the Milky Way several times in the past.
Sgr dSph should not be confused with the Sagittarius Dwarf Irregular Galaxy, or the Sag DIG, a small galaxy 3.4 million light-years distant.
Officially discovered in 1994, by Rodrigo Ibata, Mike Irwin, and Gerry Gilmore, Sgr dSph was immediately recognized as being the nearest known neighbor to the Milky Way at the time. (Since 2003, the newly discovered Canis Major Dwarf Galaxy is considered the actual nearest neighbor). Although it is one of the closest companion galaxies to the Milky Way, the main parent cluster is on the opposite side of the galactic core from Earth, and consequently is very faint, although covering a large area of the sky. Sgr dSph appears to be an older galaxy, with little interstellar dust and composed largely of Population II stars, older and metal-poor, as compared to the Milky Way. No neutral hydrogen gas related to Sgr dSph has been found.
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