NGC 4395

NGC 4395 is a low surface brightness spiral galaxy with a halo that is about 8′ in diameter. It has several wide areas of greater brightness running northwest to southeast. The one furthest southeast is the brightest. Three of the patches have their own NGC numbers: 4401, 4400, and 4399 running east to west.[3]

NGC 4395 spiral galaxy in 32 inch Schulman telescope
NGC 4395 in 32 inch telescope

The nucleus of NGC 4395 is active and the galaxy is classified as a Seyfert. It is notable for containing one of the smallest supermassive black hole with an accurately-determined mass.[4] The central black hole has a mass of "only" 300,000 Sun masses,[5] which would make it a so-called "intermediate-mass black hole".

NGC 4395
Ngc4395
An ultraviolet image of NGC 4395 taken with GALEX.
Credit: GALEX/NASA
Observation data (J2000 epoch)
ConstellationCanes Venatici[1]
Right ascension 12h 25m 48.9s[2]
Declination+33° 32′ 48″[2]
Redshift319 ± 1 km/s[2]
Distance~14 million light-years
Apparent magnitude (V)10.6[2]
Characteristics
TypeSA(s)m[2]
Size50,000 ly (diameter)
Apparent size (V)13′.2 × 11′.0[2]
Other designations
NGC 4395,[3] UGC 7542,[2] PGC 40596[2]
NGC 4395 Hubble WikiSky
NGC 4395 by HST

References

  1. ^ Celestia version 1.4.1. Laurel, Chris, 2006.
  2. ^ a b c d e f g h "NASA/IPAC Extragalactic Database". Results for. Retrieved 2006-11-04.
  3. ^ a b Kepple, George Robert; Glen W. Sanner (1998). The Night Sky Observer's Guide, Volume 2. Willmann-Bell, Inc. p. 48. ISBN 978-0-943396-60-6.
  4. ^ Merritt, David (2013). Dynamics and Evolution of Galactic Nuclei. Princeton, NJ: Princeton University Press. ISBN 9781400846122.
  5. ^ Peterson, Bradley; et al. (2005). "Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. I. A Reverberation-based Measurement of the Black Hole Mass". The Astrophysical Journal. 632 (2): 799–808. arXiv:astro-ph/0506665. Bibcode:2005ApJ...632..799P. doi:10.1086/444494.
Central massive object

Central massive object (CMO) refers to a mass concentration at the center of a galaxy. It can be either a supermassive black hole or a nuclear star cluster.

The most massive galaxies are thought to always contain a supermassive black hole (SBH); these galaxies do not contain nuclear star clusters, and the CMO is identified with the SBH. Fainter galaxies usually contain a nuclear star cluster (NSC). In most of these galaxies it is not known whether a supermassive black hole is present, and the CMO is identified with the NSC. A few galaxies, for instance the Milky Way and NGC 4395, are known to contain both a SBH and a NSC.The mass associated with CMOs is roughly 0.1–0.3% times the total mass of the galactic bulge.

Intermediate-mass black hole

An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range 102-105 solar masses: significantly more than stellar black holes but less than the 105-109 solar mass supermassive black holes. Several IMBH candidate objects have been discovered in our galaxy and others nearby, based on indirect gas cloud velocity and accretion disk spectra observations of various evidentiary strength.

List of most massive black holes

This is an ordered list of the most massive black holes so far discovered (and probable candidates), measured in units of solar masses (M☉), or the mass of the Sun (approx. 2×1030 kilograms).

List of spiral galaxies

A spiral galaxy is a type of galaxy characterized by a central bulge of old Population II stars surrounded by a rotating disc of younger Population I stars. A spiral galaxy maintains its spirals arms due to density wave theory.

M94 Group

The M94 Group (Canes Venatici I Group) is a loose, extended group of galaxies located about 13 million light-years away in the constellations Canes Venatici and Coma Berenices. The group is one of many groups that lies within the Virgo Supercluster (i.e. the Local Supercluster) and one of the closest groups to the Local Group.

Although the galaxies in this cluster appear to be from a single large cloud-like structure, many of the galaxies within the group are only weakly gravitationally bound, and some have not yet formed stable orbits around the center of this group. Instead, most of the galaxies in this group appear to be moving with the expansion of the universe.

Seyfert galaxy

Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous, distant and bright sources of electromagnetic radiation) with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.Seyfert galaxies account for about 10% of all galaxies and are some of the most intensely studied objects in astronomy, as they are thought to be powered by the same phenomena that occur in quasars, although they are closer and less luminous than quasars. These galaxies have supermassive black holes at their centers which are surrounded by accretion discs of in-falling material. The accretion discs are believed to be the source of the observed ultraviolet radiation. Ultraviolet emission and absorption lines provide the best diagnostics for the composition of the surrounding material.Seen in visible light, most Seyfert galaxies look like normal spiral galaxies, but when studied under other wavelengths, it becomes clear that the luminosity of their cores is of comparable intensity to the luminosity of whole galaxies the size of the Milky Way.Seyfert galaxies are named after Carl Seyfert, who first described this class in 1943.

Supermassive black hole

A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, containing a mass of the order of hundreds of thousands, to billions times, the mass of the Sun (M☉). This is a class of astronomical objects that has undergone gravitational collapse, leaving behind a spheroidal region of space from which nothing can escape; not even light. Observational evidence indicates that all, or nearly all, massive galaxies contain a supermassive black hole, located at the galaxy's center. In the case of the Milky Way, the supermassive black hole corresponds to the location of Sagittarius A* at the Galactic Core. Accretion of interstellar gas onto supermassive black holes is the process responsible for powering quasars and other types of active galactic nuclei.

Unbarred spiral galaxy

An unbarred spiral galaxy is a type of spiral galaxy without a central bar, or one that is not a barred spiral galaxy. It is designated with an SA in the galaxy morphological classification scheme.

The Sombrero Galaxy is an unbarred spiral galaxy.

Barless spiral galaxies are one of three general types of spiral galaxies under the de Vaucouleurs system classification system, the other two being intermediate spiral galaxy and barred spiral galaxy. Under the Hubble tuning fork, it is one of two general types of spiral galaxy, the other being barred spirals.

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