The Sombrero Galaxy (also known as Messier Object 104, M104 or NGC 4594) is a peculiar galaxy of unclear

classification Classification is the activity of assigning objects to some pre-existing classes or categories. This is distinct from the task of establishing the classes themselves (for example through cluster analysis). Examples include diagnostic tests, identif ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

borders of

Virgo Virgo may refer to: Arts and entertainment * Virgo (film), a 1970 Egyptian film * Virgo (character), several Marvel Comics characters * Virgo Asmita, a character in the manga ''Saint Seiya: The Lost Canvas'' * ''Virgo'' (album), by Virgo Four, ...

and Corvus, being about from the Milky Way galaxy. It is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the

Virgo Supercluster The Local Supercluster (LSC or LS), or Virgo Supercluster is a formerly defined supercluster containing the Virgo Cluster and Local Group, which itself contains the Milky Way and Andromeda galaxies, as well as others. At least 100 galaxy group ...

. It has an isophotal diameter of approximately , making it slightly bigger in size than the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

. It has a bright nucleus, an unusually large central bulge, and a prominent dust lane in its outer disk, which from Earth is viewed almost edge-on. The dark dust lane and the bulge give it the appearance of a sombrero hat (thus the name). Astronomers initially thought the halo was small and light, indicative of a spiral galaxy; but the Spitzer Space Telescope found that the halo was significantly larger and more massive than previously thought, indicative of a giant elliptical galaxy. The galaxy has an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

of +8.0, making it easily visible with amateur telescopes, and is considered by some authors to be the galaxy with the highest absolute magnitude within a radius of 10 megaparsecs of the Milky Way. Its large bulge, central

supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (). Black holes are a class of astronomical ...

, and dust lane all attract the attention of professional astronomers.

Observation history

Discovery

The Sombrero Galaxy was discovered on May 11, 1781 by

Pierre Méchain Pierre François André Méchain (; 16 August 1744 – 20 September 1804) was a French astronomer and surveyor who, with Charles Messier, was a major contributor to the early study of deep-sky objects and comets. Life Pierre Méchain was bo ...

, who described the object in a May 1783 letter to J. Bernoulli that was later published in the ''Berliner Astronomisches Jahrbuch''. Charles Messier made a handwritten note about this and five other objects (now collectively recognized as M104 – M109) to his personal list of objects now known as the Messier Catalogue, but it was not "officially" included until 1921.

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

independently discovered the object in 1784 and additionally noted the presence of a "dark stratum" in the galaxy's disc, what is now called a dust lane. Later astronomers were able to connect Méchain's and Herschel's observations.

Designation as a Messier object

In 1921, Camille Flammarion found Messier's personal list of the Messier objects including the hand-written notes about the Sombrero Galaxy. This was identified with object 4594 in the

New General Catalogue The ''New General Catalogue of Nebulae and Clusters of Stars'' (abbreviated NGC) is an astronomical catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, including galaxy, galaxies, star cluste ...

, and Flammarion declared that it should be included in the Messier Catalogue. Since this time, the Sombrero Galaxy has been known as ''M104''.

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 symmetrical ring that encloses the bulge of the galaxy. Most of the cold atomic hydrogen gas and the dust lie within this ring. The ring might also contain most of the Sombrero Galaxy's cold molecular gas, although this is an inference based on observations with low resolution and weak detections. Additional observations are needed to confirm that the Sombrero galaxy's molecular gas is constrained to the ring. Based on

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...

, the dust ring is the primary site of star formation within this galaxy.

Nucleus

The nucleus of the Sombrero Galaxy is classified as a

low-ionization nuclear emission-line region A low-ionization nuclear emission-line region (LINER) is a type of galactic nucleus that is defined by its spectral line emission. The spectra typically include line emission from weakly ionized or neutral atoms, such as O, O+, N+, and S ...

(LINER). These are nuclear regions where ionized gas is present, but the ions are only weakly ionized (i.e. the atoms are missing relatively few electrons). The source of energy for ionizing the gas in LINERs has been debated extensively. Some LINER nuclei may be powered by hot, young stars found in

star formation Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...

regions, whereas other LINER nuclei may be powered by active galactic nuclei (highly energetic regions that contain

s).

Infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

observations have demonstrated that the nucleus of the Sombrero Galaxy is probably devoid of any significant star formation activity. However, a supermassive black hole has been identified in the nucleus (as discussed in the subsection below), so this active galactic nucleus is probably the energy source that weakly ionizes the gas in the Sombrero Galaxy.

Central supermassive black hole

In the 1990s, a research group led by John Kormendy demonstrated that a

is present within the Sombrero Galaxy. Using

data from both the CFHT and the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

, the group showed that the speed of revolution of the stars within the center of the galaxy could not be maintained unless a mass 1 billion times that of the Sun, , is present in the center. This is among the most massive black holes measured in any nearby galaxy, and is the nearest billion-solar-mass black hole to Earth.

Synchrotron radiation

radio Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...

and

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

wavelengths, the nucleus is a strong source of synchrotron radiation. Synchrotron radiation is produced when high-velocity electrons oscillate as they pass through regions with strong

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

s. This emission is quite common for active galactic nuclei. Although radio synchrotron radiation may vary over time for some active galactic nuclei, the luminosity of the radio emission from the Sombrero Galaxy varies only 10–20%.

Unidentified terahertz radiation

In 2006, two groups published measurements of the

terahertz radiation Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic waves within the International Telecommunicat ...

from the nucleus of the Sombrero Galaxy at a wavelength of . This terahertz radiation was found not to originate from the thermal emission from dust (which is commonly seen at

and submillimeter wavelengths), synchrotron radiation (which is commonly seen at

wavelengths), bremsstrahlung emission from hot gas (which is uncommonly seen at millimeter wavelengths), or molecular gas (which commonly produces submillimeter spectral lines). The source of the terahertz radiation remains unidentified.

Globular clusters

The Sombrero Galaxy has a relatively large number of

globular cluster A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...

s, observational studies of which have produced population estimates in the range of 1,200 to 2,000. The ratio of globular clusters to the galaxy's total luminosity is high compared to the

and similar galaxies with small bulges, but comparable to other galaxies with large bulges. These results have often been used to demonstrate that the number of a galaxy's globular clusters is thought to be related to the size of its bulge. The surface density of the globular clusters generally follows the bulge's light profile, except near the galaxy's center.

Distance, mass and brightness

At least two methods have been used to measure the distance to the Sombrero Galaxy. The first method relies on comparing the measured fluxes from the galaxy's

planetary nebula A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to planets. The ...

e to the known

luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...

of planetary nebulae in the

. This method gave the distance to the Sombrero Galaxy as . The second method is the

surface brightness fluctuation Surface brightness fluctuation (SBF) is a secondary standard candle, distance indicator used to estimate distances to galaxies. It is useful to 100 Mpc (parsec). The method measures the variance in a galaxy's light distribution arising from fluc ...

s method, which uses the grainy appearance of the galaxy's bulge to estimate the distance to it. Nearby galaxy bulges appear very grainy, while more distant bulges appear smooth. Early measurements using this technique gave distances of . Later, after some refinement of the technique, a distance of was measured. This was even further refined in 2003 to . The average distance measured through these two techniques is . The mass of M104 is estimated to be 800 billions solar masses The galaxy's absolute magnitude (in the blue) is estimated as −21.9 at (−21.8 at the average distance of above)—which, as stated above, makes it the brightest galaxy in a radius of around the Milky Way. A 2016 report used the

to measure the distance to M104 based on the tip of the red-giant branch method, yielding 9.55 ± 0.13 ± 0.31 Mpc.

Nearby galaxies and galaxy group information

The Sombrero Galaxy lies within a complex, filament-like cloud of galaxies that extends to the south of the Virgo Cluster. However, it is unclear whether it is part of a formal galaxy group. Hierarchical methods for identifying groups, which determine group membership by considering whether individual galaxies belong to a larger aggregate of galaxies, typically produce results showing that the Sombrero Galaxy is part of a group that includes NGC 4487, NGC 4504, NGC 4802, UGCA 289, and possibly a few other galaxies. However, results that rely on the

percolation In physics, chemistry, and materials science, percolation () refers to the movement and filtration, filtering of fluids through porous materials. It is described by Darcy's law. Broader applications have since been developed that cover connecti ...

method (also known as the friends-of-friends method), which links individual galaxies together to determine group membership, indicate that either the Sombrero Galaxy is not in a group or that it may be only part of a galaxy pair with UGCA 287. Besides that, M104 is also accompanied by an ultra-compact dwarf galaxy, discovered in 2009, with an absolute magnitude of −12.3, an

effective radius In applied sciences, the equivalent radius (or mean radius) is the radius of a circle or sphere with the same perimeter, area, or volume of a non-circular or non-spherical object. The equivalent diameter (or mean diameter) (D) is twice the equiva ...

of just , and a mass of 3.3×

Amateur astronomy

The Sombrero Galaxy is 11.5° west of Spica and 5.5° north-east of Eta Corvi. Although it is visible with 7×35 binoculars or a amateur telescope, an telescope is needed to distinguish the bulge from the disk, and a 10- or 12-inch (250 or 300 mm) telescope to see the dark dust lane.

In culture

One artistic work referencing the Sombrero Galaxy is the song "South of the Sombrero Galaxy" by St. Louis folk metal band Ars Arcanum. The gritty sci-fi Western piece is told from the perspective of a man on the run, from both the law and his own troubled past. The Sombrero Galaxy serves as a backdrop for the song’s narrative, blending cosmic imagery with themes of pursuit and regret.

Gallery

File:Sombrero Galaxy (NIRCam) (2025-127).png, M104 imaged by

James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. As the largest telescope in space, it is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, Lis ...

's NIRCam in 2025 File:Sombrero Galaxy in infrared (Ssc2005-11a3).jpg, M104 in infrared by the Spitzer Space Telescope

Notes

References

External links

*
Hubble Mosaic of the Majestic Sombrero Galaxy (ESA)

HubbleSite: The Majestic Sombrero Galaxy (M104)

M104, the Sombrero Galaxy (NightSkyInfo.com)

Sombrero Galaxy: A Great Observatories View

*
Sombrero Galaxy (Messier 104) at Constellation Guide

South of the Sombrero Galaxy On YouTube
{{DEFAULTSORT:Sombrero Galaxy Elliptical galaxies Spiral galaxies LINER galaxies Virgo (constellation) Messier objects NGC objects 042407 17810511 Discoveries by Pierre Méchain Peculiar galaxies 293 12373-1120 -02-32-020