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The Bizarre Life of Eta Carinae A and Other Supergiant Stars

June 6, 2018


I’ve talked before about the biggest stars in the galaxy, and I’ve told you about the smallest.


But then, there are stars like Eta Carinae A - a star so massive, it seems to defy the laws of physics.


Eta Carinae A is five million times brighter than the Sun, one of the brightest stars in the galaxy. It’s so luminous that its gravity can barely contain the outward pushing pressure of its radiation.  So, it's constantly shedding mass, and yet it's still about ninety times as massive as the Sun.


With all these freaky features, this star has been dazzling astronomers for centuries.


For observers here on Earth things, started to get weird with Eta Carinae A back in the early 1800s. It began flickering faster and faster, like the warning light on a bomb that's about to explode


Then in 1837, it suddenly erupted, pouring out so much gas into space that it lost nearly the equivalent of the mass of the Sun.


Every year afterwards, it grew in brightness until it was the second brightest star in the sky, and stayed that way for more than twenty years.


Eta Carinae A released nearly as much energy as a supernova, but at a slower rate. By the time its outburst was finished, it released so much gas and debris that it actually created a nebula around itself.


Nearly a century later, astronomers decided to call it a homunculus nebula because apparently, they thought it looked like a plump little man (I think it looks like a peanut).


Eta Carinae A is an example of the most extreme types of stellar heavyweight stars that are among the most massive in the galaxy, with luminosities that are millions of times higher than the Sun’s. And since their surfaces are tens of thousands of degrees, other stars like Eta Carinae A appear to be blue!


Astronomers call them luminous blue variables or LBVs. Stars this massive tend to go through huge outbursts, but catching them the act is tricky because these outbursts are very short in length.


The lifetimes of these extreme high-mass stars are short already; keep in mind most stars including the Sun lose some mass through their stellar winds but LBVs are the biggest losers, sometimes shedding half of their original mass.


Since Eta Carinae A’s eruption in the 1800s, astronomers have continued observing her and have been able to make highly detailed 3D models of this funky-looking homunculus nebula today.



These models help untangle how the streams of hot ionized gases flowing from the star interact with each other, and it's one of the few astrophysical structures that has been fully modeled in 3D.


However, there are still a lot of questions that we can't answer yet, like how exactly the LBV phase fits into the end of a high-mass star’s life. Plus, we don't even know how these high-mass stars form in the first place.


But we do know that some formerly LBV stars have gone supernova soon after they erupted. So, Eta Carinae A may still have one more explosion in the works which means we may have one more amazing spectacle to look forward to from one of the most unusual stars in the sky.


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Sources: This story was originally published on SciShow Space. I am republishing a lightly edited version on SkyFeed in light of interest in the subject. Reimers, Reid. "The Strange Case of Eta Carinae A." SciShow Space, YouTube. 25 Feb, 2015. Web video.

Citation: Rovira, Lia N. "The Bizarre Life of Eta Carinae A and Other Supergiant Stars." SkyFeed. 6 June 2018. Web article.

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