Editing Binary star (section)

===Runaways and novae===
[[File:Artist's illustration of scenario for plasma ejections from V Hydrae.jpg|thumb|Artist rendering of [[coronal mass ejection|plasma ejection]]s from [[V Hydrae]]]]
It is also possible for widely separated binaries to lose gravitational contact with each other during their lifetime, as a result of external perturbations. The components will then move on to evolve as single stars. A close encounter between two binary systems can also result in the gravitational disruption of both systems, with some of the stars being ejected at high velocities, leading to [[runaway star]]s.<ref>{{cite journal | first1 = R. | last1 = Hoogerwerf | first2 = J.H.J. | last2 = de Bruijne | first3 = P.T. | last3 = de Zeeuw | title = The Origin of Runaway Stars | journal = Astrophysical Journal | date = December 2000 | volume = 544 | issue = 2 | pages = L133 | doi = 10.1086/317315 | bibcode=2000ApJ...544L.133H |arxiv = astro-ph/0007436 | s2cid = 6725343 }}</ref>

If a [[white dwarf]] has a close companion star that overflows its [[Roche lobe]], the white dwarf will steadily [[accretion (astrophysics)|accrete]] gases from the star's outer atmosphere. These are compacted on the white dwarf's surface by its intense gravity, compressed and heated to very high temperatures as additional material is drawn in. The white dwarf consists of [[degenerate matter]] and so is largely unresponsive to heat, while the accreted hydrogen is not. [[Nuclear fusion|Hydrogen fusion]] can occur in a stable manner on the surface through the [[CNO cycle]], causing the enormous amount of energy liberated by this process to blow the remaining gases away from the white dwarf's surface. The result is an extremely bright outburst of light, known as a [[nova]].<ref>{{cite book | first = D. | last = Prialnik | chapter = Novae | title = Encyclopaedia of Astronomy and Astrophysics | date = 2001 | pages = 1846–1856}}</ref>

In extreme cases this event can cause the white dwarf to exceed the [[Chandrasekhar limit]] and trigger a [[supernova]] that destroys the entire star, another possible cause for runaways.<ref>{{cite book | first = I. | last = Icko | chapter = Binary Star Evolution and Type I Supernovae | title = Cosmogonical Processes | date = 1986 | page = 155}}</ref><ref>{{Cite book | title = Relativistic Flows in Astrophysics | first = R. | last = Fender| chapter = Relativistic Outflows from X-ray Binaries ('Microquasars') |bibcode = 2002LNP...589..101F | date = 2002 | volume = 589 | issue = 101 | arxiv = astro-ph/0109502 | pages = 101–122 | doi = 10.1007/3-540-46025-X_6 | series = Lecture Notes in Physics | isbn = 978-3-540-43518-1 }}</ref> An example of such an event is the supernova [[SN 1572]], which was observed by [[Tycho Brahe]]. The [[Hubble Space Telescope]] recently{{when|date=September 2023}} took a picture of the remnants of this event.