Low surface brightness galaxy
Encyclopedia
A low surface brightness galaxy, or LSB galaxy, is a diffuse galaxy
with a surface brightness
that, when viewed from Earth
, is at least one magnitude lower than the ambient night sky.
Most LSBs are dwarf galaxies
, and most of their baryon
ic matter is in the form of neutral gaseous hydrogen, rather than stars. They appear to have over 95% of their mass as non-baryon
ic dark matter
. There appears to be no supernova activity in these galaxies.
Rotation curve measurements indicate an extremely high mass-to-light ratio, 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
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 more well-studied high-surface brightness galaxies, LSBs are mainly isolated field galaxies, 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 Dr. Michael J. Disney. The first LSB galaxy verified to exist was Malin 1
, 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)..
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
with a surface brightness
Surface brightness
The overall brightness of an extended astronomical object such as a galaxy, star cluster, or nebula, can be measured by its total magnitude, integrated magnitude or integrated visual magnitude; a related concept is surface brightness, which specifies the brightness of a standard-sized piece of an...
that, when viewed from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, is at least one magnitude lower than the ambient night sky.
Most LSBs are dwarf galaxies
Dwarf galaxy
A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars...
, and most of their baryon
Baryon
A baryon is a composite particle made up of three quarks . Baryons and mesons belong to the hadron family, which are the quark-based particles...
ic matter is in the form of neutral gaseous hydrogen, rather than stars. They appear to have over 95% of their mass as non-baryon
Baryon
A baryon is a composite particle made up of three quarks . Baryons and mesons belong to the hadron family, which are the quark-based particles...
ic dark matter
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
. There appears to be no supernova activity in these galaxies.
Rotation curve measurements indicate an extremely high mass-to-light ratio, 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
Bulge (astronomy)
In astronomy, a bulge is a tightly packed group of stars within a larger formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies...
s of normal spiral galaxies. Therefore they seem to be dark matter
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
-dominated even in their centers which makes them excellent laboratories for the study of dark matter.
In comparison to the more well-studied high-surface brightness galaxies, LSBs are mainly isolated field galaxies, 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 Dr. Michael J. Disney. The first LSB galaxy verified to exist was Malin 1
Malin 1
Malin 1 is a giant low surface brightness disk galaxy which is 650,000 light years across; 5 and a half times the size of our Milky Way. It was the first LSB galaxy verified to exist, and as such, is the first giant LSB galaxy identified. Its high surface brightness central spiral is 30,000 light...
, 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)..
Examples
- Andromeda VAndromeda VAndromeda V is a dwarf spheroidal galaxy about 2.52 Mly away in the constellation Andromeda.-History:Andromeda V was discovered by Armandroff et al...
- Pegasus Dwarf Spheroidal GalaxyPegasus Dwarf Spheroidal GalaxyThe Pegasus Dwarf Spheroidal is a dwarf spheroidal galaxy about 2.7 million light-years away in the constellation Pegasus...
- IC 10IC 10IC 10 is an irregular galaxy in the constellation Cassiopeia. It was discovered by Lewis Swift in 1887. Nicholas U. Mayall was the first to suggest that the object is extragalactic in 1935. Edwin Hubble suspected it might belong to the Local Group of galaxies, but its status remained uncertain for...
- Malin 1Malin 1Malin 1 is a giant low surface brightness disk galaxy which is 650,000 light years across; 5 and a half times the size of our Milky Way. It was the first LSB galaxy verified to exist, and as such, is the first giant LSB galaxy identified. Its high surface brightness central spiral is 30,000 light...
- Malin 2
- Phoenix Dwarf Galaxy
- Sagittarius Dwarf Irregular GalaxySagittarius Dwarf Irregular GalaxyThe Sagittarius Dwarf Irregular Galaxy or SagDIG is a dwarf galaxy in the constellation of Sagittarius. It lies about 3.4 million light-years away. SagDIG should not be confused with the Sagittarius Dwarf Elliptical Galaxy or SagDEG, a satellite galaxy of the Milky Way. It was discovered by...
(SagDIG) - Sextans ASextans ASextans A , is a tiny dwarf irregular galaxy. It spans about 5000 light-years across, and is located within the Local Group of galaxies, which includes our Milky Way galaxy. At 4.3 million light-years away from Earth, Sextans A is one of most distant members of the Local Group, and is notable for...
- Sextans BSextans BSextans B 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 most distant members of the Local Group, if it is indeed a member. It forms a pair with its neighbouring galaxy Sextans A...
- Wolf-Lundmark-Melotte Galaxy (WLM)