The Sombrero Galaxy (also known as Spiral Galaxy M104, Messier Object 104, Messier 104, M104, H1.43, or NGC 4594) is a spiral galaxy in the Virgo constellation. It was discovered in the late 1700s. On May 11, 1781, Charles Messier added it by hand to his personal copy of the Messier catalog after its initial publication, describing it as a "very faint nebula". The object is mentioned as a discovery in a May 6, 1783 letter by Pierre Méchain, and was independently discovered by William Herschel on May 9, 1784.
General information
M104, also known as H1.43 and NGC 4594, lies in the constellation Virgo. It is about 28 million light years away, closer than the Virgo cluster, of which it is generally not considered a member. It is an 8th magnitude spiral galaxy of type Sa or Sb, just faint enough to be invisible to the naked eye but easily visible with small telescopes. In our sky, it is about one-fifth the diameter of the full moon. The diameter of M104 is inconsistently cited as being from 50,000 to 140,000 light years in diameter. According to STSci's HubbleSite, M104's diameter is 50,000 light years and it has a mass of about 800 billion Suns. It has a large, bright core, an unusually large central bulge, and a prominent dust lane, or band of dust in the galactic disc. Because it is seen edge-on, these features give it the appearance of a Mexican hat, hence the name Sombrero Galaxy.
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. Recent photos reveal that the galaxy has a very extended galactic halo.
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.
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