Dropout (astronomy)
Encyclopedia
In astronomy
, dropout is a radiation
source whose radiation intensity falls off sharply above a specific wavelength
. 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
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
ed and can be used to determine the distance to the galaxy.
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, dropout is a radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
source whose radiation intensity falls off sharply above a specific wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
. 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
Hubble Deep Field
The Hubble Deep Field is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area 2.5 arcminutes across, two parts in a million of the whole sky, which is equivalent in angular size to a 65 mm tennis...
. Because the hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
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
Redshift
In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
ed and can be used to determine the distance to the galaxy.