The Sombrero Galaxy, also known as Messier 104 (M104), is a famous unbarred spiral galaxy located in the southern skies, in the direction of Virgo constellation. It lies at a distance of 29.3 million light years from Earth. The galaxy’s designation in the New General Catalogue is NGC 4594.
The Sombrero Galaxy is known for its appearance, similar to that of a Mexican hat, with a bright white core surrounded by thick lanes of dust and a halo of globular clusters and stars, appearing almost edge-on when observed from Earth.
Messier 104 has an exceptionally large and prominent central bulge, which contains billions of very old stars that are responsible for the glow of the galaxy’s central region. The dust lanes contain a number of younger, brighter stars.
M104 is believed to contain a large black hole at its centre. The central region is quite bright across the electromagnetic spectrum. With an apparent visual magnitude of 8.98, the galaxy can’t be seen without binoculars, but it can easily be found in smaller telescopes.
The Sombrero Galaxy can be seen in 7×35 binoculars or a 4-inch telescope. The galaxy’s central bulge can be made out in a medium-sized telescope, and the dust lane is visible in larger telescopes, starting from 10-inch and 12-inch telescopes.
To distinguish the galaxy’s bulge from the disk, one needs at least an 8-inch telescope.
Images from NASA’s Spitzer Space Telescope have revealed that Messier 104 has a significantly larger and more massive halo surrounding it than previously believed, which suggests that it might really be a giant elliptical galaxy.
In 2012, infrared images from Spitzer indicated that the Sombrero Galaxy is really two galaxies in one: a large elliptical galaxy with a thin disk galaxy embedded within.
The galaxy’s halo, seen glowing in visible light images, was revealed to be the right mass and size for a large elliptical galaxy.
The discovery raised questions over the galaxy’s formation because what would usually be the most likely scenario – the giant elliptical galaxy swallowing the smaller spiral galaxy – does not make sense here because the smaller galaxy’s disk would most likely not have survived the collision.
Another theory suggests that a cloud of dust was drawn in by the gravity of the elliptical galaxy, and formed a spinning disk around the galaxy’s centre.
The Sombrero Galaxy is believed to be similar to Centaurus A, another elliptical galaxy with an embedded disk inside it, located in Centaurus constellation.
The Sombrero Galaxy was discovered by the French astronomer Pierre Méchain on May 11, 1781. Charles Messier did not include the galaxy in his original catalogue, but it was one of the six objects he noted that were later added to the list of Messier objects.
Messier 104 was added to the Messier Catalogue in 1921 by the French astronomer and author Camille Flammarion. He discovered Messier’s notes about the galaxy, which was identified with NGC 4594 in the New General Catalogue, and suggested that the object be included on the list of Messier objects.
The galaxy was independently discovered by the German-British astronomer William Herschel in 1784, who noted the “dark stratum,” or dust lane, in the galaxy’s disk.
The dust lane in M104 is composed mainly of dust and hydrogen gas. It is the main site of star formation within the galaxy, and contains most of the galaxy’s cold molecular gas.
The galaxy has a mass of approximately 800 billion suns. It contains almost 2,000 globular clusters, which is 10 times as many as those orbiting the Milky Way. The clusters are believed to be between 10 and 13 billion years old, roughly the same age as those orbiting our galaxy.
Messier 104 is moving away from us at the speed of more than 1,000 kilometres per second. The galaxy’s recession speed was first measured in 1912. At the time, it was the largest redshift ever measured and one of the first indicators that the Universe was expanding.
The galaxy’s nucleus is classified as a low ionization nuclear emission region (LINER), and an unlikely site for any significant star forming activity.
The Sombrero Galaxy is believed to belong to a group of galaxies that include NGC 4504, NGC 4487, NGC 4802, UGCA 289, and possibly several other galaxies.
The supermassive black hole at the heart of the Sombrero Galaxy is one of the most massive black holes detected in galaxies near the Milky Way. It is believed to have a mass of at least a billion suns. This would make it about 250 times larger than the black hole in the centre of our galaxy, the Milky Way.
The supermassive black hole at the centre of Messier 104 was discovered by a team led by John Kormendy in the 1990s. They used information obtained from the Hubble Space Telescope and the Canada France Hawaii Telescope to demonstrate that the stars near the galaxy’s centre could not maintain their speed of revolution unless the centre contained a mass equal to that of a billion suns.
LOCATION AND SIZE
The Sombrero Galaxy is located in Virgo constellation, at the southern edge of the Virgo Cluster, approximately 29.3 million light years from Earth. It is about 50,000-60,000 light years across, which makes it slightly smaller than the Milky Way Galaxy.
The galaxy can be found 11.5 degrees to the west of the bright star Spica and 5.5 degrees to the northeast of Eta Corvi in Corvus constellation. It lies near the border between Virgo and Corvus.
Spica can be easily located in the sky by following the arc of the Big Dipper‘s handle. The line leads first to Arcturus in Boötes constellation, the fourth brightest star in the sky, and then to Spica, the brightest star in Virgo and the 15th brightest star in the night sky.
Sombrero Galaxy – Messier 104 (NGC 4594)
Distance: 29.3 ± 1.6 million light years (8,600 kiloparsecs)
Coordinates: 12h39m59.4s (right ascension), -11°37’23” (declination)
Visual magnitude: 8.98
Apparent dimensions: 8′.7×3’x5
Redshift: 0.003416 ± 0.000017
Designations: Messier 104 (M104), NGC 4594, PGC 42407, UGC 293, GC 3132