astronomy Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...

, dropout is a

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

source whose radiation intensity falls off sharply below a specific

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

. The source will be easily visible when its light is filtered to wavelengths longer than the cutoff value, but will "drop out" of the image when it is filtered to wavelengths shorter than the threshold. This is a standard method for locating distant galaxies in deep field images. Because the

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

that surrounds the galaxies absorbs light with a wavelength around 100 nanometers, the galaxies have a natural dropout threshold. The exact wavelength of this threshold is

redshift 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 f ...

ed and can be used to determine the distance to the galaxy.

References

Extragalactic astronomy {{physical-cosmology-stub

See also

References