NGC 4494 is an

elliptical galaxy An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The R ...

located 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 origins of the e ...

Coma Berenices Coma Berenices is an ancient asterism in the northern sky, which has been defined as one of the 88 modern constellations. It is in the direction of the fourth galactic quadrant, between Leo and Boötes, and it is visible in both hemisphere ...

. It is located at a distance of circa 45 million light years from Earth, which, given its apparent dimensions, means that NGC 4494 is about 60,000 light years across. It was discovered by

William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...

in 1785.

Characteristics

The galaxy hosts a

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 obj ...

with estimated mass 26.9 ± 20.4 millions M⊙, based on velocity dispersion. A nuclear dust ring has been detected in NGC 4494, based on observations by the

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

. It has semimajor axis 0.6 arcseconds, which corresponds to 60 parsec at the distance of NGC 4494. Its ring is symmetric, implying that the dust has settled in this galaxy, after the

galaxy merger Galaxy mergers can occur when two (or more) galaxies collide. They are the most violent type of galaxy interaction. The gravitational interactions between galaxies and the friction between the gas and dust have major effects on the galaxies i ...

with a relatively gas rich galaxy that led to its creation. The core of NGC 4494 is kinematically decoupled, as with many elliptical galaxies, probably a result of a galaxy merger.

Dark matter

In observations by

XMM-Newton ''XMM-Newton'', also known as the High Throughput X-ray Spectroscopy Mission and the X-ray Multi-Mirror Mission, is an X-ray space observatory launched by the European Space Agency in December 1999 on an Ariane 5 rocket. It is the second cornerst ...

observatory, the galaxy was quite faint in

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

s, nearly two orders of magnitude fainter than galaxies with similar optical luminosities. This fact has been attributed to lack of

dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...

and hot gas of the galaxy. The amount of dark matter existing in the

halo Halo, halos or haloes usually refer to: * Halo (optical phenomenon) * Halo (religious iconography), a ring of light around the image of a head HALO, halo, halos or haloes may also refer to: Arts and entertainment Video games * ''Halo'' (franch ...

of NGC 4494 has been debated. The galaxy is characterised as "naked" by Romanowsky et al., Napolitano et al. found that the dark matter halo has unexpectedly low central density and the analysis by Deason et al. revealed an unusually low dark matter fraction, 0.32 ± 0.12 at 5Re. Rodionov and Athanassoula tried to set strict constraint to the halo mass, but with only partial success. On the other hand, Morganti et al. found the dark matter fraction to be about 0.6 ± 0.1 at 5Re, with particularly high dark matter fraction inside ∼ 3Re.

Nearby galaxies

NGC 4494 belongs to the NGC 4565 group, named after the spiral galaxy

NGC 4565 NGC 4565 (also known as the Needle Galaxy or Caldwell 38) is an edge-on spiral galaxy about 30 to 50 million light-years away in the constellation Coma Berenices. It lies close to the North Galactic Pole and has a visual magnitude of approximatel ...

. Other members of the group are NGC 4525,

NGC 4562 NGC commonly refers to: * New General Catalogue of Nebulae and Clusters of Stars, a catalogue of deep sky objects in astronomy NGC may also refer to: Companies * NGC Corporation, name of US electric company Dynegy, Inc. from 1995 to 1998 * Nati ...

, NGC 4570, NGC 4725 and

NGC 4747 NGC commonly refers to: * New General Catalogue of Nebulae and Clusters of Stars, a catalogue of deep sky objects in astronomy NGC may also refer to: Companies * NGC Corporation, name of US electric company Dynegy, Inc. from 1995 to 1998 * Nati ...

. NGC 4494 is also a member of the

Coma I Group The Coma I Group is a group of galaxies located about away in the constellation Coma Berenices. The brightest member of the group is NGC 4725. The Coma I Group is rich in spiral galaxies while containing few elliptical and lenticular galaxies. ...

which is part of the

Virgo Supercluster The Virgo Supercluster (Virgo SC) or the Local Supercluster (LSC or LS) is a mass concentration of galaxies containing the Virgo Cluster and Local Group, which itself contains the Milky Way and Andromeda galaxies, as well as others. At least ...

Gallery

File:NGC 4494 u3cm6602r core.jpg, The nucleus of NGC 4494 by

. File:NGC4494 - SDSS DR14.jpg, SDSS image of NGC 4494

References

External links

{{DEFAULTSORT:NGC 4494 Elliptical galaxies Coma Berenices 4494 07662 41441 Coma I Group