Editing White dwarf (section)

=== Post-common envelope binary ===
{{Main|Post common envelope binary}}
A post-common envelope binary (PCEB) is a binary consisting of a white dwarf or [[hot subdwarf]] and a closely tidally-locked red dwarf (in other cases this might be a [[brown dwarf]] instead of a red dwarf).<ref>{{cite journal|title=A Catalog of Potential Post–Common Envelope Binaries |first1=Matthias U. |last1=Kruckow |first2=Patrick G. |last2=Neunteufel |first3=Rosanne |last3=Di Stefano |first4=Yan |last4=Gao |first5=Chiaki |last5=Kobayashi |journal=The Astrophysical Journal |date=2021 |arxiv=2107.05221 |volume=920 |number=2 |page=86 |doi=10.3847/1538-4357/ac13ac|doi-access=free |bibcode=2021ApJ...920...86K }}</ref> These binaries form when the red dwarf is engulfed in the [[red giant]] phase. As the red dwarf orbits inside the [[common envelope]], it is slowed down in the denser environment. This slowed orbital speed is compensated with a decrease of the orbital distance between the red dwarf and the core of the red giant. The red dwarf spirals inwards towards the core and might merge with the core. If this does not happen and instead the common envelope is ejected, then the binary ends up in a close orbit, consisting of a white dwarf and a red dwarf. This type of binary is called a post-common envelope binary. The evolution of the PCEB continues as the two dwarf stars orbit closer and closer due to [[magnetic braking (astronomy)|magnetic braking]] and by releasing gravitational waves. The binary might then evolve into one of several dramatic outcomes: a high-field magnetic white dwarf, a white dwarf pulsar, a double-degenerate binary, or even a Type Ia supernova.<ref>{{cite journal|first1=J. |last1=Nordhaus |first2=S. |last2=Wellons |first3=D. S. |last3=Spiegel |first4=B. D. |last4=Metzger |first5=E. G. |last5=Blackman |title=Formation of high-field magnetic white dwarfs from common envelopes |journal=PNAS |volume=108 |number=8 |pages=3135–3140 |doi=10.1073/pnas.1015005108 |year=2011|doi-access=free |pmid=21300910 |pmc=3044383 |arxiv=1010.1529 |bibcode=2011PNAS..108.3135N }}</ref><ref>{{cite journal|first1=A. |last1=Rebassa-Mansergas |first2=E. |last2=Solano |first3=F. M. |last3=Jiménez-Esteban |first4=S. |last4=Torres |first5=C. |last5=Rodrigo |first6=A. |last6=Ferrer-Burjachs |first7=L. M. |last7=Calcaferro |first8=L. G. |last8=Althaus |first9=A. H. |last9=Córsico |title=White dwarf–main-sequence binaries from Gaia EDR3: the unresolved 100 pc volume-limited sample |journal=Monthly Notices of the Royal Astronomical Society |volume=506 |number=4 |date=October 2021 |pages=5201–5211 |doi=10.1093/mnras/stab2039|doi-access=free |arxiv=2107.06303 }}</ref> Because a PCEB may evolve at some point into a [[cataclysmic variable]], some of them are also called pre-cataclysmic variables.<ref>{{cite journal|first1=M. R. |last1=Schreiber |first2=B. T. |last2=Gänsicke |title=The age, life expectancy, and space density of Post Common Envelope Binaries |journal=Astronomy and Astrophysics |volume=406 |pages=305–321 |year=2003 |doi=10.1051/0004-6361:20030801|arxiv=astro-ph/0305531 |bibcode=2003A&A...406..305S }}</ref><ref name="GaiaDR3"/>