Nuller

Nulling interferometry

Interferometry is used in astronomy to achieve a higher spatial resolution by combining the light of several telescopes. The technique is based on the wave nature of light. It has been developed and is now in the radio interferometry applied also in the infrared range and in visible light. Normally, the light of the telescopes is superimposed so that amplify the signals for the target object, ie interfere constructively.

For the observation of faint objects around bright stars is the modified concept of nulling interferometer of interest. Here the light of the telescopes is superimposed so that the signals for the target object extinguish ( the star ) each other ( ' zero '). In the simplest case of the two telescopes applies when the signals from both telescopes for the target object by a half wavelength are exactly out of phase. The extinction is not for the faint objects in the vicinity, whose light has traveled a different way and has a different shift. Such objects are thus visible with better contrast.

Application

From the new technology of nulling interferometry is hoped that in the future faint objects to be discovered in the vicinity of stars. These objects include exoplanets, dust disks and the asteroid belt. These objects can not be filtered out of the glare of their host stars in the optical spectral range with today's detectors ( except in exceptional cases faint stars or from a long distance between star and planet ).

A similar effect as a nulling interferometer also has the Koronograf, but which is based on an entirely different principle. A Koronograf blocks the light of a star on an opaque material in the beam path of a telescope, and thus makes for example the faint corona of our sun is visible ( hence the name Koronograf ).

History and Future

The concept of nulling interferometry was proposed in 1979 by Ronald N. Bracewell and Robert H. MacPhie. In 1997, at the Multiple Mirror Telescope on Mount Hopkins (Arizona ), a demonstration experiment successfully. Today is the nulling interferometry basis of many under construction and planned experiments and satellites to search for exoplanets, such as GENIE ( a building under construction test experiment for the Very Large Telescope ), the setting into operation in autumn 2005 Large Binocular Telescope in Arizona and some space telescopes such as the (now gestrichenenen for cost reasons) Terrestrial Planet Finder ( TPF ), NASA and the ESA also painted Darwin, which was to go on the search for Earth-like planets from 2015.