Sagittarius Dwarf Elliptical Galaxy
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| No image. | |
| Observation data: J2000 epoch | |
|---|---|
| Constellation: | Sagittarius |
| Right ascension: | 18h 55m 19.5s[2] |
| Declination: | -30° 32′ 43″[2] |
| Redshift: | 140 ± ? km/s[2] |
| Distance: | 65 ± 7 kly (20 ± 2 kpc)[3][4] |
| Type: | dSph(t)[2] |
| Apparent dimensions (V): | 450′.0 × 216′.0[2] |
| Apparent magnitude (V): | 4.5[2] |
| Notable features: | Heading for a collision with the Milky Way |
| Other designations | |
| SagDEG,[citation needed] Sgr dSph,[2] |
|
| See also: Galaxy, List of galaxies | |
The Sagittarius Dwarf Elliptical Galaxy (SagDEG) is an elliptically looped shaped satellite galaxy of the Milky Way Galaxy. The main cluster which, in 1994, was the first to be discovered, is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth and traveling in a polar orbit 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). It should not be confused with the Sagittarius Dwarf Irregular Galaxy (Sag DIG).
Further discoveries by astrophysics teams from both the Universities of Virginia and Massachusetts, drawing upon the 2MASS Two-Micron All Sky Infrared Survey data, revealed the entire looped shaped structure. In 2003 with the aid of infrared telescopes, and super computers, Steven Majewski, Michael Skrutskie, and Martin Weinberg were able to help create a new star map [David Law] distinguishing the full Sagittarius Dwarf presence, position, and looping shape out from the mass of background stars and found this smaller galaxy to be at a near right angle to the plane of the Milky Way.[5]
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 it covers a large area of the sky. Officially discovered in 1994, by Rodrigo Ibata, Mike Irwin, and Gerry Gilmore, Sag DEG was immediately recognized as being the nearest known neighbor to our Milky Way at the time. Sag DEG appears to be an older galaxy, with little interstellar dust and composed largely of Population II stars, older and metal-poor compared to the Milky Way.
Based on its current trajectory, the Sag DEG main cluster is poised to pass through the galactic disc of the Milky Way within the next hundred million years, while the extended looped shaped ellipse is actually even now extended around and through our local space and on through the Milky Way galactic disc in process of slowly being absorbed into the larger galaxy, calculated at 10,000 times the mass of Sag DEG.
The exact history and future of Sag DEG are very much under debate as the discoveries that continue to pour in are causing the necessary rewriting of all earlier theories faster than anticipated.
At first, many astronomers thought that Sag DEG had already reached an advanced state of destruction, so that a large part of its original matter was already mixed with that of the Milky Way. However, Sag DEG still has coherence as a dispersed elongated ellipse, and appears to move in a roughly polar orbit around the Milky Way as close as 50,000 light-years from the galactic core. Although it may have begun as a ball of stars before falling towards the Milky Way, Sag DEG is now being torn apart by immense tidal forces over hundreds of millions of years. Numerical simulations suggest that stars ripped out from the dwarf would be spread out in a long stellar stream along its path, which were subsequently detected.
However, some astronomers contend that Sag DEG has been in orbit around the Milky Way for some billions of years, and has already orbited it around ten times. Its ability to retain some coherence despite such strains would indicate an unusually high concentration of dark matter within that galaxy.
On the other hand, others note the similarity of star types between Sag DEG and the Large Magellanic Cloud, arguing that it has recently gone into orbit about our galaxy having somehow become detached.
Sag DEG has several globular clusters with one, M54, apparently residing at its core.
From its discovery until 2003, it was considered to be the closest outside galaxy to Earth, but since then has been overtaken by the newly discovered Canis Major Dwarf Galaxy.
Sag DEG should not be confused with Sag DIG, the Sagittarius Dwarf Irregular Galaxy, a small galaxy over 4 million light-years distant.
[edit] See also
[edit] External links
[edit] References
- ^ SIMBAD Astronomical Database. Results for Sagittarius Dwarf Spheroidal. Retrieved on November 28, 2006.
- ^ a b c d e f g h i NASA/IPAC Extragalactic Database. Results for Sagittarius Dwarf Spheroidal. Retrieved on November 28, 2006.
- ^ I. D. Karachentsev, V. E. Karachentseva, W. K. Hutchmeier, D. I. Makarov (2004). "A Catalog of Neighboring Galaxies". Astronomical Journal 127: 2031-2068.
- ^ Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics 49 (1): 3-18.
- ^ http://www.astro.virginia.edu/~mfs4n/sgr/sgr_big.jpg
 Galactic Core: Center of the Milky Way |
