Eta Carinae B is the hidden partner of Eta Carinae, a hot blue star no telescope has separated from its huge companion, known only by what it does.
At a glance
| type | blue giant (class O) |
|---|---|
| distance from the Sun | 7,500 light-years (2.3 kpc) |
| its light left it | 7,500 years ago |
| luminosity | 400,000 × the Sun |
| radius | 14 × the Sun |
| surface temperature | 37,000 K |
Read off the piece’s own catalogue, the same values it draws with.
About Eta Carinae B
Eta Carinae is a pair. The brighter star is one of the most massive and unstable stars known, wrapped in the Homunculus, the twin-lobed cloud it threw off in its great eruption. Its partner, Eta Carinae B, is a hot O-type star on a long, very elongated orbit that swings it close to the primary and then far away again.
Nobody has seen it directly; the glare of the primary and the surrounding nebula hide it. It is revealed by a cycle. Each time the two stars pass closest, the X-rays from the region where their winds collide flare and then collapse, and lines in the spectrum fade and return. The regularity of that cycle is what proved there are two stars.
Its ultraviolet light also matters: it ionises gas close to the system that the primary alone could not, so some of the nebula’s glow is its work. Both stars sit inside the Carina Nebula, one of the richest star-forming regions in the Galaxy.
What you see in the piece
Fly to Eta Carinae and B sits beside the primary, a blue-white point far closer than any amateur telescope could split. Both are buried in the Carina Nebula, so dust reddens and dims them from the Sun’s side.
Measured or modelled
Its temperature, size and power are inferred from the collision of the winds and from models of the orbit, not measured from its own light; the values on the card are estimates that differ between studies.
Questions
Has Eta Carinae B ever been seen?
Not directly. It is known from a repeating cycle in the X-rays and spectrum of Eta Carinae, which changes every time the two stars pass close to each other.
How far away is Eta Carinae B?
It is 7,500 light-years (2.3 kpc) from the Sun, with its companion inside the Carina Nebula.