Editing Eta Carinae (section)

===Homunculus===
{{main|Homunculus Nebula}}
[[File:3D Homunculus Nebula.jpg|right|thumb|upright=1.2|alt=3D model of Homunculus Nebula, shown from front and rear, on either side of an actual image|A 3D model of the Homunculus Nebula]]
η&nbsp;Carinae is enclosed by, and lights up, the [[Homunculus Nebula]],<ref name="aitken">{{cite journal|bibcode=1975MNRAS.172..141A|title=The infrared spectrum and structure of Eta Carinae|journal=Monthly Notices of the Royal Astronomical Society|volume=172|pages=141–147|last1=Aitken|first1=D. K.|last2=Jones|first2=B.|year=1975|doi=10.1093/mnras/172.1.141|doi-access=free}}</ref> a small emission and reflection nebula composed mainly of gas ejected during the Great Eruption event in the mid-19th century, as well as dust that condensed from the debris. The nebula consists of two [[Bipolar nebula|polar lobes]] aligned with the rotation axis of the star, plus an equatorial "skirt", the whole being around {{val|18|ul=arcsecond}} long.<ref name="abraham">{{cite journal |last1=Abraham |first1=Zulema |last2=Falceta-Gonçalves |first2=Diego |last3=Beaklini |first3=Pedro P.B. |title=Η Carinae Baby Homunculus Uncovered by ALMA |journal=The Astrophysical Journal |volume=791 |issue=2 |pages=95 |year=2014 |bibcode=2014ApJ...791...95A |arxiv=1406.6297 |s2cid=62893264 |doi=10.1088/0004-637X/791/2/95}}</ref> Closer studies show many fine details: a ''Little Homunculus'' within the main nebula, probably formed by the 1890 eruption; a jet; fine streams and knots of material, especially noticeable in the skirt region; and three Weigelt Blobs—dense gas condensations very close to the star itself.<ref name="johansson"/><ref name="weigelt">{{cite journal |last1=Weigelt |first1=G. |last2=Ebersberger |first2=J. |title=Eta Carinae resolved by speckle interferometry |journal=Astronomy and Astrophysics |volume=163 |pages=L5 |year=1986 |issn=0004-6361 |bibcode=1986A&A...163L...5W}}</ref>

The lobes of the Homunculus are considered to be formed almost entirely due to the initial eruption, rather than shaped by or including previously ejected or interstellar material, although the scarcity of material near the equatorial plane allows some later stellar wind and ejected material to mix. Therefore, the mass of the lobes gives an accurate measure of the scale of the Great Eruption, with estimates ranging from {{solar mass|12–15}} up to as high as {{solar mass|45}}.<ref name="impostors"/><ref name="morris"/><ref name="gomez">{{cite journal|doi=10.1111/j.1745-3933.2009.00784.x|title=Submillimetre variability of Eta Carinae: Cool dust within the outer ejecta|journal=Monthly Notices of the Royal Astronomical Society: Letters|volume=401|issue=1|pages=L48–L52|year=2010|last1=Gomez|first1=H.L. |last2=Vlahakis|first2=C. |last3=Stretch|first3=C.M. |last4=Dunne|first4=L. |last5=Eales |first5=S.A. |last6=Beelen |first6=A. |last7=Gomez|first7=E.L. |last8=Edmunds |first8=M.G. |display-authors=6 |doi-access=free |bibcode=2010MNRAS.401L..48G|arxiv = 0911.0176|s2cid=119295262}}</ref> The results show that the material from the Great Eruption is strongly concentrated towards the poles; 75% of the mass and 90% of the kinetic energy were released above latitude 45°.<ref name="smith2006">{{cite journal|doi=10.1086/503766|title=The Structure of the Homunculus. I. Shape and latitude dependence from H<sup>II</sup> and [Fe<sup>II</sup>] velocity maps of η&nbsp;Carinae |journal=[[The Astrophysical Journal]] |volume=644|issue=2|pages=1151–1163|year=2006|last1=Smith|first1=Nathan|bibcode=2006ApJ...644.1151S|arxiv = astro-ph/0602464|s2cid=12453761}}</ref>

A unique feature of the Homunculus is the ability to measure the spectrum of the central object at different latitudes by the reflected spectrum from different portions of the lobes. These clearly show a ''polar wind'' where the stellar wind is faster and stronger at high latitudes thought to be due to rapid rotation causing [[gravity darkening|gravity brightening]] towards the poles. In contrast the spectrum shows a higher excitation temperature closer to the equatorial plane.<ref name="latitude">{{cite journal|doi=10.1086/367641|title=Latitude-dependent Effects in the Stellar Wind of η Carinae|journal=The Astrophysical Journal|volume=586|issue=1|pages=432–450|year=2003 |last1=Smith|first1=Nathan|last2=Davidson|first2=Kris|last3=Gull|first3=Theodore R.|last4=Ishibashi|first4=Kazunori|last5=Hillier|first5=D. John|bibcode=2003ApJ...586..432S |arxiv = astro-ph/0301394 |s2cid=15762674}}</ref> By implication the outer envelope of η&nbsp;Carinae A is not strongly convective as that would prevent the [[gravity darkening]]. The current axis of rotation of the star does not appear to exactly match the alignment of the Homunculus. This may be due to interaction with η&nbsp;Carinae B which also modifies the observed stellar winds.<ref name="groh2010"/>