Nuller
Encyclopedia
A nuller is a tool used to block out a strong source so that fainter signals near the source can be observed. An example of a nuller is being employed on the Keck Interferometer. This causes the light
from a star
to destructively interfere, effectively cancelling out the star's image
. The faint light from an orbiting ring of dust can then be detected. This project is part of a scientific effort to detect and observe nearby planet
s.
Nulling interferometry is a type of interferometry
in which two or more signals are mixed to produce observational regions in which the incoming signals cancel themselves out. This creates a set of virtual "blind spots" which prevent unwanted signals from those areas from interfering with weaker nearby signals.
In 1978 Australian-American astronomer Ronald N. Bracewell
suggested using nulling interferometry to search for planets around other stars
. This technique is being considered for use by the Terrestrial Planet Finder
, a NASA
mission. Also the ESA Darwin
mission is considering the use of it. It is being used on the Keck Interferometer.
This technique is similar to a coronagraph
but uses multiple sources rather than a physical obstacle to block out the unwanted signals.
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
from a star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
to destructively interfere, effectively cancelling out the star's image
Image
An image is an artifact, for example a two-dimensional picture, that has a similar appearance to some subject—usually a physical object or a person.-Characteristics:...
. The faint light from an orbiting ring of dust can then be detected. This project is part of a scientific effort to detect and observe nearby planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
s.
Interferometry
Interferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...
in which two or more signals are mixed to produce observational regions in which the incoming signals cancel themselves out. This creates a set of virtual "blind spots" which prevent unwanted signals from those areas from interfering with weaker nearby signals.
In 1978 Australian-American astronomer Ronald N. Bracewell
Ronald N. Bracewell
Ronald Newbold Bracewell AO was the Lewis M. Terman Professor of Electrical Engineering, Emeritus of the at Stanford University.- Education :...
suggested using nulling interferometry to search for planets around other stars
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
. This technique is being considered for use by the Terrestrial Planet Finder
Terrestrial Planet Finder
The Terrestrial Planet Finder was a proposed project by NASA to construct a system of telescopes for detecting extrasolar terrestrial planets. TPF was postponed several times and finally cancelled...
, a NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
mission. Also the ESA Darwin
Darwin (ESA)
Darwin was a suggested ESA Cornerstone mission which would have involved a constellation of four to nine spacecraft designed to directly detect Earth-like planets orbiting nearby stars and search for evidence of life on these planets...
mission is considering the use of it. It is being used on the Keck Interferometer.
This technique is similar to a coronagraph
Coronagraph
A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved...
but uses multiple sources rather than a physical obstacle to block out the unwanted signals.