Editing Convection zone (section)

==Main sequence stars==
{{See also|Radiation zone#Stability against convection}}
In [[main sequence stars]] more than 1.3 times the mass of the Sun, the high core temperature causes [[nuclear fusion]] of [[hydrogen]] into [[helium]] to occur predominantly via the [[CNO cycle|carbon-nitrogen-oxygen (CNO) cycle]] instead of the less temperature-sensitive [[proton–proton chain]].  The high temperature gradient in the core region forms a convection zone that slowly mixes the hydrogen fuel with the helium product. The core convection zone of these stars is overlaid by a [[radiation zone]] that is in thermal equilibrium and undergoes little or no mixing.<ref>{{cite journal|doi=10.1051/0004-6361:20010585|arxiv = astro-ph/0105054 |bibcode = 2001A&A...373..190B |title = Formation of massive stars by growing accretion rate |journal = Astronomy and Astrophysics |volume = 373 |pages = 190–198 |year = 2001 |last1 = Behrend |first1 = R. |last2 = Maeder |first2 = A. |s2cid = 18153904 }}</ref>  In the most massive stars, the convection zone may reach all the way from the core to the surface.<ref>{{cite journal|doi=10.1051/0004-6361/201321282|arxiv = 1304.3337 |bibcode = 2013A&A...554A..23M |title = Evidence of quasi-chemically homogeneous evolution of massive stars up to solar metallicity |journal = Astronomy & Astrophysics |volume = 554 |pages = A23 |year = 2013 |last1 = Martins |first1 = F. |last2 = Depagne |first2 = E. |last3 = Russeil |first3 = D. |last4 = Mahy |first4 = L. |s2cid = 54707309 }}</ref>

In main sequence stars of less than about 1.3 solar masses, the outer envelope of the star contains a region where partial [[ionization]] of [[hydrogen]] and [[helium]] raises the heat capacity.  The relatively low temperature in this region simultaneously causes the [[Opacity (optics)|opacity]] due to heavier elements to be high enough to produce a steep temperature gradient. This combination of circumstances produces an outer convection zone, the top of which is visible in the Sun as [[Granule (solar physics)|solar granulation.]] Low-mass main-sequence stars, such as [[red dwarf]]s below 0.35 [[solar mass]]es,<ref name=aaa496_3_787>{{cite journal
 | last1=Reiners | first1=Ansgar | last2=Basri | first2=Gibor
 | title=On the magnetic topology of partially and fully convective stars
 | journal=Astronomy and Astrophysics | volume=496 | issue=3 | pages=787–790
 |date=March 2009 | doi=10.1051/0004-6361:200811450
 | bibcode=2009A&A...496..787R |arxiv = 0901.1659 | s2cid=15159121 }}</ref> as well as pre-main sequence stars on the [[Hayashi track]], are convective throughout and do not contain a radiation zone.<ref name=antona>{{cite journal|doi=10.1051/0004-6361:20031410 |arxiv = astro-ph/0309348 |bibcode = 2003A&A...412..213D |title = Efficiency of convection and Pre-Main Sequence lithium depletion |journal = Astronomy and Astrophysics |volume = 212 |pages = 213–218 |year = 2003 |last1 = d'Antona |first1 = F. |last2 = Montalbán |first2 = J. |s2cid = 2590382 }}</ref>

In main sequence stars similar to the Sun, which have a radiative core and convective envelope,  the transition region between the convection zone and the [[radiation zone]] is called the [[tachocline]].