Binary star system. The primary is a peculiar B-star similar to a luminous blue variable that initially had around 150 solar masses and has since lost at least 30. Because of its mass and the stage of its life, it is expected to explode as a supernova or hypernova in the astronomically near future. This is currently the only star known to produce ultraviolet laser emission. The secondary star is hot and also highly luminous, of spectral class O, around 30 times as massive as Sol.

Previously a 4th-magnitude star, it brightened in 1837 to become brighter than Rigel marking the start of the Great Eruption. Eta Carinae became the second-brightest star in the sky between 11 and 14 March 1843 before fading well below naked eye visibility after 1856. In a smaller eruption, it reached 6th magnitude in 1892 before fading again. It has brightened consistently since about 1940, becoming brighter than magnitude 4.5 by 2014.