5 Eta Carinae

The repeat detonator

Despite early claims that the Pistol Star was the most luminous star ever found, it’s actually three-times dimmer than Eta Carinae. The latter was originally recorded at fourth magnitude, but in a 20-year event called the ‘Great Eruption’ it dramatically blazed to become the brightest star in the sky. It subsequently dimmed, brightened, dimmed and then increased in luminosity again from the 1940s. Today it sits at magnitude +4.3.

This changeable luminosity was triggered by

Eta Carinae’s ejection of the Homunculus Nebula, a cloud of ionised hydrogen whose light reached Earth in 1841. Condensation of dust from the nebula is thought to have been responsible for this cyclic brightening and dimming. Eta Carinae is 5 million times more luminous than our Sun. It was believed to be one of the most massive stars, but in 2005 it was found that it was actually a binary system.

Its primary may have reached 150 to 250 solar masses in its youth, but has sustained one of the highest rates of mass loss ever recorded for a star. Eta Carinae’s extreme luminosity and low gravity seem to have caused this loss, and it is believed that it shed ten to 20 solar masses in the Great Eruption. Its primary could go supernova tomorrow, or thousands of years from now.

“IT DRAMATICALLY BLAZED TO BECOME THE BRIGHTEST STAR IN THE SKY”