Editing White dwarf (section)

=== Other multiple-star systems ===
Other binaries include those that consist of a [[Main-sequence star|main sequence star]] (or giant) and a white dwarf. The binary Sirius AB is an example pair of this type.<ref>{{cite book|first1=Andrew |last1=Fraknoi |display-authors=etal |title=Astronomy 2e |publisher=OpenStax |isbn=978-1-951693-50-3 |year=2024 |chapter=18.4 The H–R Diagram |chapter-url=https://openstax.org/books/astronomy-2e/pages/18-4-the-h-r-diagram |page=618}}</ref> White dwarfs can also exist as binaries or multiple star systems that only consist of white dwarfs. An example of a resolved triple white dwarf system is [[WD J1953−1019]], discovered with [[Gaia DR2]] data.<ref>{{cite journal|first1=M. |last1=Perpinyà-Vallès |first2=A. |last2=Rebassa-Mansergas |first3=B. T. |last3=Gänsicke |first4=S. |last4=Toonen |first5=J. J. |last5=Hermes |first6=N. P. |last6=Gentile Fusillo |first7=P.-E. |last7=Tremblay |title=Discovery of the first resolved triple white dwarf |journal=Monthly Notices of the Royal Astronomical Society |volume=483 |number=1 |date=February 2019 |pages=901–907 |doi=10.1093/mnras/sty3149|doi-access=free |arxiv=1811.07752 }}</ref> One interesting field is the study of [[#Debris disks and planets|remnant planetary systems]] around white dwarfs. It is expected that planets orbiting several [[Astronomical unit|AU]] from a star will survive the star's post-main-sequence transformation into a white dwarf. Moreover, white dwarfs, being much smaller and correspondingly less luminous than their progenitors, are less likely to outshine any bodies in orbit around them. This makes white dwarfs advantageous targets for direct-imaging searches for [[exoplanet]]s and [[brown dwarf]]s. The first brown dwarf to be detected by direct imaging was the companion to the white dwarf [[GD 165|GD 165 A]], discovered in 1988.<ref>{{cite journal|first1=Wolfgang |last1=Brandner |first2=Hans |last2=Zinnecker |first3=Taisiya |last3=Kopytova |title=Search for giant planets around seven white dwarfs in the Hyades cluster with the Hubble Space Telescope |journal=Monthly Notices of the Royal Astronomical Society |year=2021 |volume=500 |issue=3 |pages=3920–3925 |doi=10.1093/mnras/staa3422 |doi-access=free |arxiv=2011.03562}}</ref> More recently, the white dwarf [[WD 0806−661]] was found to have a cold companion body of substellar mass, variously described as a brown dwarf<ref>{{cite journal | last1=Luhman |first1=K. L. |last2=Burgasser |first2=A. J. |last3=Bochanski |first3=J. J. | year=2011 | title=Discovery of a Candidate for the Coolest Known Brown Dwarf | journal=The Astrophysical Journal Letters |volume=730 |number=1 |pages=L9 |arxiv=1102.5411 |doi=10.1088/2041-8205/730/1/L9 |bibcode=2011ApJ...730L...9L }}</ref><ref>{{cite journal |last1=Rodriguez |first1=David R. |last2=Zuckerman |first2=B. |last3=Melis |first3=Carl |last4=Song |first4=Inseok |date=May 2011 |title=The Ultra Cool Brown Dwarf Companion of WD 0806-661B: Age, Mass, and Formation Mechanism |journal=The Astrophysical Journal Letters |volume=732 |number=2 |pages=L29 |doi=10.1088/2041-8205/732/2/L29 |arxiv=1103.3544 |bibcode=2011ApJ...732L..29R }}</ref> or an exoplanet.<ref>{{cite journal|first1=Dimitri |last1=Veras |first2=N. Wyn |last2=Evans |title=Exoplanets beyond the Solar neighbourhood: Galactic tidal perturbations |journal=Monthly Notices of the Royal Astronomical Society |volume=430 |number=1 |date=21 March 2013 |pages=403–415 |doi=10.1093/mnras/sts647 |doi-access=free |arxiv=1212.4150}}</ref>