101 must-see cosmic objects: M104

Dust is a common component of spiral galaxies. Astronomers believe this dust is carbon- or silicate-rich and no more than 0.25 microns wide. This does not greatly affect the brightness of galaxies, except in cases where they appear almost edge-on; then, their orientation captures the maximum amount of dust. The Sombrero Galaxy (M104), named for its resemblance to the famous wide-brimmed Mexican hat, is by far the brightest galaxy with a prominent equatorial dust belt.

It’s not exactly on the edge, but at 6° wide, it’s very close. This 6° tilt allows us to see the nuclear region and makes the asymmetrical star hub visible above and below the dark lane. A bright core contains a massive but silent black hole with a billion solar masses.

M104 was discovered by Pierre Méchain in 1781. He passed the information on to his observing partner, Charles Messier, who added it to his list of non-cometary objects. But the comet-watcher’s more detailed thoughts on this and other more numerous objects in his list were not known until Camille Flammarion, popularizer of French astronomy, published the Messier’s notes in 1921.

Designated NGC 4594 in John Dreyer’s New General Catalog of Nebulae and Star Clusters, this 9th magnitude galaxy is classified as the Sa type, known for having a large central hub relative to its spiral arms. The arms are tightly coiled and lack large HII regions. With dimensions of 8.7′ by 3.5′ at 29 million light years away, the Sombrero is about 50,000 light years in diameter, half the size of our home galaxy. .

For observers who have never seen a dust belt in a galaxy, M104 is an excellent first target because it is observable with modest telescopes. Under a good sky, it is within range of a 6-inch telescope. As the aperture increases, more detail is visible along the edge of the dark path and the bright core becomes better resolved. Try observing this object with multiple apertures during a star party.

The Sombrero is easy to find, just 11° west of Spica (Alpha [α] Virginias). It is located in Virgo – but barely, as it lies slightly north of the border with Corvus and northeast of Eta (η) Corvi.


Be sure to explore the full list of 101 cosmic objects you must see on Astronomy. New entries will be added weekly throughout 2022.

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