Supernova Imposter Has Been Faking It For Longer Than We Thought

Natural colour image of Eta Carinae and the gas that surrounds it. HST/NASA/ESA

Apparently, you can’t even trust stars to be what they look like. A supreme example is Eta Carinae, a complex system believed to be a supernova in the 19th century but later discovered to be faking it. And now, new research suggests that it has been faking it for a long time.

American researchers have carefully analyzed images of Eta Carinae, a system made up of two large stars surrounded by a nebula, and discovered that the “Great Eruption” of the mid-1800s was just one of at least three mass ejections that have been happening in the last 700 years.

"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," said lead author Megan Kiminki, a doctoral student from the University of Arizona, in a statement.

In a paper, available online and soon to be published in the Monthly Notices of the Royal Astronomical Society, the scientists aligned images of the binary star-system taken over many years and realized that Eta Carinae was surrounded by more than 800 gas blobs.

By estimating their velocities, the team derived that this material was expelled by the star in two separate eruptions in the mid-13th and mid-16th centuries – meaning it "faked" a supernova at least three times.

"We don't really know what's going on with Eta Carinae," Kiminki added. "But knowing that Eta Carinae erupted at least three times tells us that whatever causes those eruptions must be a recurring process because it wouldn't be very likely that each eruption is caused by a different mechanism."

One of the stars in the system is nearing the end of its life, meaning it might soon become a real supernova. Since Eta Carinae is about 7,000 light-years from Earth, it might already have happened and we are yet to see it.

"Even though we still have not figured out the underlying physical mechanism that caused the 19th-century eruption, we now know that it isn’t a one-time event," said co-author Nathan Smith, also from the University of Arizona.

"That makes it harder to understand, but it is also a critical piece of the puzzle of how very massive stars die. Stars like Eta Carinae apparently refuse to go quietly into the night."

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