A nuller is an optical tool used to block a strong source so that fainter signals near that source can be observed. An example of a nuller is being employed on the Keck Interferometer. This causes the

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

from a

star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...

to destructively interfere, effectively cancelling the star's

image An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensio ...

. As a result, the faint light from a ring of dust orbiting the star can then be detected. This project is part of a scientific effort to detect and observe nearby

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a ...

Interferometry

''Nulling interferometry'' is a type of

interferometry Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber o ...

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 Newbold Bracewell AO (22 July 1921 – 12 August 2007) was the Lewis M. Terman Professor of Electrical Engineering of the Space, Telecommunications, and Radioscience Laboratory at Stanford University. Education Bracewell was born i ...

suggested using nulling interferometry to search for planets around other stars. This technique was considered for use by both the Terrestrial Planet Finder (a canceled

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedi ...

mission) and

Darwin Darwin may refer to: Common meanings * Charles Darwin (1809–1882), English naturalist and writer, best known as the originator of the theory of biological evolution by natural selection * Darwin, Northern Territory, a territorial capital city i ...

(a canceled

ESA , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1 ...

mission). It is being used on the Keck Interferometer. A different technique is called a

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. Most coronagraphs are intended to view t ...

, using a physical obstacle to block the unwanted signals.

Experimental nullers

There has been a nuller built by the Jet Propulsion Laboratory that has flown on a NASA sounding rocket twice, once in 2011 and a second time in 2015. There is also a laboratory nuller at NASA Goddard Space Flight Center known as the Visible Nulling Coronagraph (VNC) that is actively conducting experiments. VNC at NASA GSFC

References

{{reflist

External links

Interferometric Nulling at TNOTutorial on nulling interferometryProgress Toward Astronomical Nulling
(Criteria governing efficacy of nulling interferometry), Chapter 10 of the Terrestrial Planet Finder (TPF): A NASA Origins Program to Search for Habitable Planets - JPL Publication 99-003, May 1999
Interactive "virtual" interferometer
Observational astronomy Optical components

Interferometry

Experimental nullers

See also

References

External links