Editing Eta Carinae (section)

===Size===
The size of the two main stars in the η&nbsp;Carinae system is difficult to determine precisely, for neither star can be seen directly. η&nbsp;Carinae B is likely to have a well-defined photosphere, and its radius can be estimated from the assumed type of star. An O&nbsp;supergiant of {{solar luminosity|933,000}} with a temperature of 37,200&nbsp;K has an effective radius of {{solar radius|23.6}}.<ref name="verner"/>

The size of η&nbsp;Carinae A is not even well defined. It has an optically dense stellar wind, so the typical definition of a star's surface being approximately where it becomes opaque gives a very different result to where a more traditional definition of a surface might be. One study calculated a radius of {{solar radius|60}} for a hot "core" of 35,000&nbsp;K at [[optical depth]] 150, near the sonic point or very approximately what might be called a physical surface. At optical depth 0.67 the radius would be {{solar radius|over 800}}, indicating an extended optically thick stellar wind.<ref name="hillier">{{cite journal |last1=Hillier |first1=D. John |last2=Davidson |first2=K. |last3=Ishibashi |first3=K. |last4=Gull |first4=T. |title=On the Nature of the Central Source in η Carinae |journal=The Astrophysical Journal |volume=553 |issue=837 |pages=837 |date=June 2001 |bibcode=2001ApJ...553..837H |doi=10.1086/320948 |doi-access=free}}</ref> At the peak of the Great Eruption the radius, so far as such a thing is meaningful during such a violent expulsion of material, would have been around {{solar radius|1,400}}, comparable to the [[List of largest known stars|largest-known]] [[red supergiant]]s, including [[VY Canis Majoris]].<ref name="smith2011b">{{cite journal |last=Smith |first=Nathan |title=Explosions triggered by violent binary-star collisions: Application to Eta Carinae and other eruptive transients |journal=Monthly Notices of the Royal Astronomical Society |volume=415 |issue=3 |pages=2020–2024 |year=2011 |bibcode=2011MNRAS.415.2020S |arxiv=1010.3770 |s2cid=119202050 |doi=10.1111/j.1365-2966.2011.18607.x|doi-access=free }}</ref>

The stellar sizes should be compared with their orbital separation, which is only around {{solar radius|250}} at periastron. The accretion radius of the secondary is around {{solar radius|60}}, suggesting strong accretion near periastron leading to a collapse of the secondary wind.<ref name="KashiSoker"/> It has been proposed that the initial brightening from 4th magnitude to 1st at relatively constant bolometric luminosity was a normal LBV outburst, albeit from an extreme example of the class. Then the companion star passing through the expanded photosphere of the primary at periastron triggered the further brightening, increase in luminosity, and extreme mass loss of the Great Eruption.<ref name="smith2011b"/>