A faint blue galaxy (FBG) is an inconspicuous, often small galaxy with low surface
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 ...
. In addition to being dim, they show a remarkably high quantity of sparsely scattered blue stars, but comparatively few red stars, which in most galaxies are by far the most common. They appear as dim, bluish smudges on old
photographic plate
Photographic plates preceded film as the primary medium for capturing images in photography. These plates, made of metal or glass and coated with a light-sensitive emulsion, were integral to early photographic processes such as heliography, d ...
s, with no clear structure or shape, and do not register well on modern
electronic cameras, which are more sensitive to red light. They are currently interpreted as small
dwarf-irregular satellite-galaxies undergoing a burst of star formation.
[
]
Previously overlooked
Although some had been previously photographed as faint smudges in sky surveys, they were first noticed in the 1970s, posing a problem for then-current theories of galaxy formation
In cosmology, the study of galaxy formation and evolution is concerned with the processes that formed a Homogeneity and heterogeneity, heterogeneous universe from a Big Bang, homogeneous beginning, the formation of the first galaxies, the way ga ...
. FBGs tend to be found in the peripheries of galaxy clusters and as remote satellites of large galaxies, and appear to be a now-finished stage of galactic growth.[ Any galaxy might appear faint because it is small or because it is far away. Neither explanation, nor any combination, matched the initial FBG observations.
]
The first faint blue galaxy problem
The faint blue galaxy (FBG) problem in astrophysics
Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline, James Keeler, said, astrophysics "seeks to ascertain the ...
first arose with observations starting in 1978 that there were more galaxies with a than then-current theory predicted.
The distribution of these galaxies has since been found to be consistent with models of cosmic inflation
In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the very early universe. Following the inflationary period, the universe continued to expand, but at a slower ...
, measurements of the cosmic microwave background
The cosmic microwave background (CMB, CMBR), or relic radiation, is microwave radiation that fills all space in the observable universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dar ...
, and a nonzero cosmological constant; that is, with the existence of the now-accepted dark energy
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure format ...
. It thus serves as a confirmation of supernova
A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
observations requiring dark energy.
The second faint blue galaxy problem
A second problem arose in 1988, with even deeper observations showing a much greater excess of faint galaxies.
References
{{Galaxy
Galaxies