The supernova that wasn’t: A tale of 3 cosmic eruptions

From University of Arizona:

IMAGE: Vectors illustrating the observed proper motions of 792 features in the ejecta of Eta Carinae. The arrows are color-coded by the date of ejection from the central star. Until now,… view more

Credit: Kiminki et al./NASA

In the mid-1800s, astronomers surveying the night sky in the Southern Hemisphere noticed something strange: Over the course of a few years, a previously inconspicuous star named Eta Carinae grew brighter and brighter, eventually outshining all other stars except Sirius, before fading again over the next decade, becoming too dim to be seen with the naked eye.

What had happened to cause this outburst? Did 19th-century astronomers witness some strange type of supernova, a star ending its life in a cataclysmic explosion?

“Not quite,” says Megan Kiminki, a doctoral student in the University of Arizona’s Department of Astronomy and Steward Observatory. “Eta Carinae is what we call a supernova impostor. The star became very bright as it blew off a lot of material, but it was still there.”

Indeed, in the mid-20th century Eta Carinae began to brighten again.

The aftermath of the “Great Eruption” of the mid-1800s, which is now readily visible through a small telescope if you happen to be in the Southern Hemisphere, made Eta Carinae a celebrity among objects in the universe known for their bizarre beauty. An hourglass-shaped, billowing cloud of glowing gas and dust enshrouds the star and its companion. Known as the Homunculus nebula, the cloud consists of stellar material hurled into space during the Great Eruption, drifting away at 2 million miles per hour.

By carefully analyzing images of Eta Carinae taken with NASA’s Hubble Space Telescope, Kiminki and her team were surprised to discover that the Great Eruption was only the latest in a …

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