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Homunculus Nebula

October 21, 2015

In the 1840s, the star known today as Eta Carina put on quite a show: It became the second-brightest star in the night sky, shining many times brighter than ever before. Over the next few decades, though, it faded from sight — only a telescope could reveal its feeble glow.

Those two episodes are related. And we’re still watching them play out.

Eta Carina consists of two giant stars. The biggest is about 90 times more massive than the Sun, and five million times brighter.

The star is so energetic, in fact, that it’s unstable. That caused it to blow out two giant bubbles of hot gas — the outburst seen in the 1840s. The bubbles contain enough material to make a dozen or more Suns.

Over time, the bubbles expanded and began to cool. That allowed some of the gas to clump together to form solid grains, known as dust. The gas and dust hid the two stars from view. In fact, it wasn’t until a few years ago that astronomers knew the system consisted of two stars instead of one.

Astronomers in the 1940s described the shape of this complex as a “homunculus” — a shape resembling a little man. Seen through today’s telescopes, though, it looks more like a dumbbell or a peanut — twin lobes of material flanking the stars.

Today, the Homunculus Nebula has expanded enough to allow more light from the stars to escape into space. So Eta Carina is once again visible to the unaided eye — a faint pinpoint surrounded by a cocoon of its own making.

Script by Damond Benningfield, Copyright 2015

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