{{Short description|Scientific Electronic Device}} A '''nuller''' is an optical instrument, e.g., a beam combiner for nulling interferometry<ref>{{Cite journal |last=Bracewell |first=R. N. |date=1978 |title=Detecting nonsolar planets by spinning infrared interferometer |url=https://www.nature.com/articles/274780a0 |journal=Nature |language=en |volume=274 |issue=5673 |pages=780–781 |doi=10.1038/274780a0 |issn=1476-4687|url-access=subscription }}</ref>, used to block or cancel out a strong source so that fainter signals near that source can be observed. This is typically useful to detect off-axis exoplanet or exozodiacal dust by interferometrically nulling out the on-axis parent star.
The VLT interferometer’s visiting instrument Asgard's<ref>{{Cite journal |last=Martinod |first=Marc-Antoine |last2=Defrère |first2=Denis |last3=Ireland |first3=Michael |last4=Kraus |first4=Stefan |last5=Martinache |first5=Frantz |last6=Tuthill |first6=Peter |last7=Bigioli |first7=Azzurra |last8=Bouzerand |first8=Emilie |last9=Bryant |first9=Julia |last10=Chhabra |first10=Sorabh |last11=Courtney-Barrer |first11=Benjamin |last12=Crous |first12=Fred |last13=Cvetojevic |first13=Nick |last14=Dandumont |first14=Colin |last15=Ertel |first15=Steve |date=2023-06-27 |title=High-angular resolution and high contrast observations from Y to L band at the Very Large Telescope Interferometer with the Asgard Instrumental suite |url=https://www.spiedigitallibrary.org/journals/Journal-of-Astronomical-Telescopes-Instruments-and-Systems/volume-9/issue-02/025007/High-angular-resolution-and-high-contrast-observations-from-Y-to/10.1117/1.JATIS.9.2.025007.full |journal=Journal of Astronomical Telescopes, Instruments, and Systems |volume=9 |issue=02 |doi=10.1117/1.JATIS.9.2.025007 |issn=2329-4124|hdl=10150/673745 |hdl-access=free }}</ref> submodule NOTT (Nulling Observations of exoplaneTs and dusT) contains such a nuller to combine four telescope signals to perform nulling interferometry<ref>{{Cite journal |last=Sanny |first=Ahmed |last2=Labadie |first2=Lucas |last3=Gross |first3=Simon |last4=Barjot |first4=Kévin |last5=Laugier |first5=Romain |last6=Garreau |first6=Germain |last7=Martinod |first7=Marc-Antoine |last8=Defrère |first8=Denis |last9=Withford |first9=Michael J. |date=2026-01-01 |title=Asgard/NOTT: L-band nulling interferometry at the VLTI - III. The mid-infrared integrated optics beam combiner for NOTT |url=https://www.aanda.org/articles/aa/abs/2026/01/aa55865-25/aa55865-25.html |journal=Astronomy & Astrophysics |language=en |volume=705 |pages=A37 |doi=10.1051/0004-6361/202555865 |issn=0004-6361|doi-access=free }}</ref>.
==Nulling interferometry== ''Nulling interferometry'' evolved from traditional stellar interferometry. The key difference is that it induces a 180-degree phase shift, for example, in one beam of a two-telescope interferometer. This creates destructive interference on the optical axis (where the star is) and constructive interference for off-axis objects (like planets). A technique initially proposed by Australian-American astronomer Ronald N. Bracewell in 1978 <ref>{{Cite journal |last=Bracewell |first=R. N. |date=1978 |title=Detecting nonsolar planets by spinning infrared interferometer |url=https://www.nature.com/articles/274780a0 |journal=Nature |language=en |volume=274 |issue=5673 |pages=780–781 |doi=10.1038/274780a0 |issn=1476-4687|url-access=subscription }}</ref>.
A different technique is called a coronagraph, using a physical obstacle to block the unwanted signals.
==See also== * Coronagraph * Interferometry
== References ==
{{reflist}}
==External links== *[http://www.tno.nl/content.cfm?&context=markten&content=case&laag1=191&item_id=600&Taal=2 Interferometric Nulling at TNO] *[http://www.daviddarling.info/encyclopedia/N/nulling.html Nulling interferometer basics] *[https://web.archive.org/web/20060905142258/http://astro1.panet.utoledo.edu/%7Endm/Visuals/baglunchsep03.pdf Tutorial on nulling interferometry] *[https://web.archive.org/web/20030622174600/http://planetquest.jpl.nasa.gov/TPF/tpf_book/Chapter_10c.pdf Progress 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 *[https://web.archive.org/web/20070630043107/http://planetquest.jpl.nasa.gov/SIM/Demo/index.cfm Interactive "virtual" interferometer]
Category:Observational astronomy Category:Optical components