Eta Carinae, approximately 7500 light-years from Earth, has everything that an astronomer could want. First, there’s the nebula surrounding Eta Carinae. The so-called Homunculus Nebula is still growing. It has the shape of two opposing cones, whose tips originate in Eta Carinae, and measures more than 0.5 light-years from end to end. From the propagation rate of up to 700 km/s, the existence of the nebula can be traced back to an outburst in the 1840s.
Second, it is not just a single star, but a binary system consisting of two blue giants. The primary star has a mass of 100 solar masses and is thus one of the most massive stars in the Milky Way. But even the secondary star is not a lightweight. It is 30 times heavier than our home star.
Both stars also orbit each other once every 5.5 years at a very close distance. Sometimes they come as close as the Sun and Mars, then move as far apart as the Sun and Uranus. At a cosmic scale, however, that is still just a stone’s throw away, and thus they inevitably each hurl large portions of their mass at each other in the form of dense, supersonic stellar winds made from charged particles. In this way, in only about 5000 years, the primary star loses as much mass as our Sun has in total. The secondary star propels a stellar wind moving at about eleven million kilometer per hour (corresponds to at least one percent of the speed of light).