Sombrero Galaxy
Encyclopedia : S : SO : SOM : Sombrero Galaxy
The Sombrero Galaxy (also known as M104 or NGC 4594) is an unbarred spiral galaxy in the constellation Virgo. M104 is the primary galaxy in the M104 group of galaxies. It has a large, bright core, an unusually large central bulge, and a prominent dust lane, or band of dust in the galactic disc. From Earth, it is seen nearly edge-on, which gives it the appearance of a sombrero. It is an 8th magnitude spiral galaxy of type Sa, easily visible with small telescopes.
Discovery
M104 was discovered in the late 1700s, most likely by Pierre Méchain, who mentioned it as a discovery in a May 6, 1783 letter. It was the first Messier object added after the initial publication of the Messier catalog. Messier added it by hand to his personal copy on May 11, 1781, describing it as a "very faint nebula". M104 was also independently discovered by William Herschel on May 9, 1784.
Early redshift measurements
In 1912, Vesto Slipher discovered that M104 has a large redshift. From this it was calculated that M104 is moving away from Earth at about 1,000 kilometers per second - a speed too high for any object residing in the Milky Way. This was one of the first solid clues that M104 was not a nebula, as was thought at the time, and that the universe is expanding in all directions.
Distance
The best distance measurements to M104 have been made by two groups using techniques involving planetary nebulae and surface brightness fluctuations. The average of these distance measurements generally place the galaxy at 9.2 Mpc, or approximately 30 million ly. At this distance, the radius of the galaxy (as seen in visible light) is approximately 38,000 ly.
Dust ring
As noted above, this galaxy's most striking feature is the dust lane that crosses in front of the bulge of the galaxy. This dust lane is actually a very symmetric ring that encloses the bulge of the galaxy . Most of the cold atomic hydrogen gas and the dust lies within this ring. The ring also appears to contain most of the cold molecular gas that fuels star formation, although these conclusions are inferences based on observations with low resolution and weak detections; additional observations are needed to confirm these results. Based on infrared spectroscopy, the dust ring is the primary cite of star formation within this galaxy.
Central supermassive black hole
In the 1990's, a research group led by John Kormendy demonstrated that a supermassive black hole is present within the Sombrero Galaxy. Using spectroscopy data from both the CFHT and the Hubble], the group showed that the speed of rotation of the stars within the center of the galaxy could not be maintained unless a mass 1 billion times the mass of the Sun, or 109Mʘ, is present in the center. This is among the most massive black holes measured in any nearby galaxies.
Globular clusters
M104 also has a well-populated system of globular clusters, with at least several hundred visible with large telescopes, and an estimated population of 2,000 or more, many more than orbit the Milky Way.
Halo
Recent photos reveal that the galaxy has a very extended galactic halo.
External links
- [Messier 104, SEDS Messier pages]
- [HubbleSite: Hubble mosaic of the majestic Sombrero Galaxy]
- [NightSkyInfo.com - M104, the Sombrero Galaxy]
Notes and references
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.