A faint blue galaxy (FBG) is an inconspicuous, often small galaxy with low surface luminosity. In addition to being dim, they show a remarkable preponderance 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 plates, with no clear structure or shape, and do not register well on modern electronic cameras, which are more sensitive to red.
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, and posed a problem for the then-current theories of galaxy formation.
FBGs tend to 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 instead 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 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, measurements of the cosmic microwave background
In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all spac ...
, and a nonzero cosmological constant; that is, with the existence of the now-accepted dark energy
In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univ ...
.
It thus serves as a confirmation of supernova 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.[
]
These are now interpreted as dwarf galaxies experiencing large bursts of stellar formation, resulting in blue light from young, massive stars.[
]
Thus FBGs are extremely bright for their size and distance.
Most FBGs appear between red-shift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in fr ...
It is inferred that they merged with other galaxies, and consequently disappeared as separate objects some time in the "recent" cosmological past.[
][
]
References
{{Galaxy
Galaxies