A low-surface-brightness galaxy, or LSB galaxy, is a diffuse galaxy with a

surface brightness In astronomy, surface brightness (SB) quantifies the apparent brightness or flux density per unit angular area of a spatially extended object such as a galaxy or nebula, or of the night sky background. An object's surface brightness depends on it ...

that, when viewed from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, is at least one magnitude lower than the ambient night sky. Most LSBs are

dwarf galaxies A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is so ...

, and most of their

baryon In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3). Baryons belong to the hadron family of particles; hadrons are composed of quarks. Baryons are also classif ...

ic matter is in the form of neutral gaseous hydrogen, rather than stars. They appear to have over 95% of their mass as non-

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 a ...

. There appears to be little supernova (SN) activity in these galaxies, although LSB galaxy IC 217 hosted 2014cl.

Rotation curve The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre. It is typically rendered graphically as a plot, ...

measurements indicate an extremely high

mass-to-light ratio In astrophysics and physical cosmology the mass-to-light ratio, normally designated with the Greek letter upsilon, , is the quotient between the total mass of a spatial volume (typically on the scales of a galaxy or a cluster) and its luminosity. T ...

, meaning that stars and luminous gas contribute only very little to the overall mass balance of an LSB. The centers of LSBs show no large overdensities in stars, unlike e.g. the

bulge __NOTOC__ Bulge may refer to: Astronomy and geography *Bulge (astronomy), a tightly packed group of stars at the center of a spiral galaxy *Equatorial bulge, a bulge around the equator of a planet due to rotation * Tharsis bulge, vast volcanic pl ...

s of normal spiral galaxies. Therefore, they seem to be dark-matter-dominated even in their centers, which makes them excellent laboratories for the study of dark matter. In comparison to the high-surface-brightness galaxies, LSBs are mainly isolated

field galaxies A field galaxy is a galaxy that does not belong to a larger galaxy group or cluster and hence is gravitationally alone. Roughly 80% of all galaxies located within of the Milky Way The Milky Way is the galaxy that includes our Solar Sys ...

, found in regions devoid of other galaxies. In their past, they had fewer tidal interactions or mergers with other galaxies, which could have triggered enhanced star formation. This is an explanation for the small stellar content. LSB galaxies were theorized to exist in 1976 by Mike Disney.

Giant low-surface-brightness galaxies

Giant low surface brightness (GLSB) galaxies are among the most massive known

spiral galaxies Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae'' They have very faint

stellar disk A galactic disc (or galactic disk) is a component of disc galaxies, such as spiral galaxies and lenticular galaxies. Galactic discs consist of a stellar component (composed of most of the galaxy's stars) and a gaseous component (mostly composed ...

s that are very rich in neutral hydrogen but low in star formation and thus low in surface brightness. Such galaxies often have bright bulges that can host low luminosity

active galactic nuclei An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not prod ...

. GLSB galaxies are usually isolated systems that rarely interact with other galaxies. The first LSB galaxy verified to exist was

Malin 1 __NOTOC__ Malin 1 is a giant low surface brightness (LSB) spiral galaxy. It is located away in the constellation Coma Berenices, near the North Galactic Pole. , it is the largest known spiral galaxy, with an approximate diameter of , thus ove ...

, discovered in 1986. As such, it was also the first giant LSB galaxy identified. At the time of its discovery, it was the largest spiral galaxy known (by scale-length measurement).Scientific American, "The Ghostliest Galaxies", GD Bothun, Vol. 276, No. 2, ''February 1997'', pp.40-45, Ken Crosswell
"Malin 1: A Bizarre Galaxy Gets Slightly Less So"
''22 January 2007'' UGC 1382 was previously thought to be an elliptical galaxy, but low-brightness spiral arms were later detected. UGC 1382 is much closer to Earth than Malin 1.

Examples

Andromeda V Andromeda V is a dwarf spheroidal galaxy about 2.52 Mly away in the constellation Andromeda. Andromeda V was discovered by Armandroff et al. and published in 1998 after their analysis of the digitized version of the second Palomar Sky Sur ...

Pegasus Dwarf Spheroidal Galaxy The Pegasus Dwarf Spheroidal (also known as ''Andromeda VI'' or ''Peg dSph'' for short) is a dwarf spheroidal galaxy about 2.7 million light-years away in the constellation Pegasus. The Pegasus Dwarf is a member of the Local Group and a sate ...

* IC 10 *

NGC 45 NGC 45 is a low surface brightness spiral galaxy in the equatorial constellation of Cetus. It was discovered on 11 November 1835 by the English astronomer John Herschel. The galaxy is located at a distance of 22 million light years an ...

Eridanus II The Eridanus II Dwarf is a low-surface brightness dwarf galaxy in the constellation Eridanus. Eridanus II was independently discovered by two groups in 2015, using data from the Dark Energy Survey ( Bechtol et al., 2015; Koposov et al. 2015) ...

* Malin 2 *

Phoenix Dwarf The Phoenix Dwarf is a dwarf irregular galaxy discovered in 1976 by Hans-Emil Schuster and Richard Martin West and mistaken for a globular cluster. It is currently 1.44 Mly away from Earth Earth is the third planet from the Sun ...

* Sagittarius Dwarf Irregular Galaxy (

SagDIG The Sagittarius Dwarf Irregular Galaxy (SagDIG) is a dwarf galaxy in the constellation of Sagittarius. (SagDIG should not be confused with the Sagittarius Dwarf Spheroidal Galaxy, SagDEG, a satellite galaxy of the Milky Way discovered decades ...

) *

Sextans A Sextans A (also known as UGCA 205) is a small dwarf irregular galaxy. It spans about 5000 light-years across, and is located at 4.3 million light-years away, in the outskirts of the Local Group of galaxies, which includes the Milky Way galaxy, an ...

Sextans B Sextans B (also known as UGC 5373 and DDO 70) is an irregular galaxy that may be part of the Local Group, or lie just beyond it. Sextans B is 4.44 million light-years away from Earth and thus is one of the most distant members of the Local Gro ...

* Wolf–Lundmark–Melotte galaxy (WLM) * UGC 477

References

*K. O'Neil
The HI Content and Extent of Low Surface Brightness Galaxies - Could LSB Galaxies be Responsible for Damped Ly-alpha Absorption?
For publication in ''Extragalactic Gas at Low Redshift'', by Mulchaey, et al., eds (2001). *S.D. Rosenbaum and D.J. Bomans
The environment of Low Surface Brightness Galaxies
''Astronomy & Astrophysics Letters'', 422, 5-8 (2004). *A.J. Barth
A normal stellar disk in the galaxy Malin 1
''

Astronomical Journal ''The Astronomical Journal'' (often abbreviated ''AJ'' in scientific papers and references) is a peer-reviewed monthly scientific journal owned by the American Astronomical Society (AAS) and currently published by IOP Publishing. It is one of th ...

'' 133, 1085-1091 (2007). {{Portal bar, Stars, Spaceflight, Outer space, Solar System

Giant low-surface-brightness galaxies

Examples

See also

References