The Homunculus Nebula looks alive. Its two lobes of gas, which resemble twin human hearts stuck artery to artery, stretch half a light-year each from its center. And they’re getting bigger all the time, swelling outward at 1.5 million miles per hour. If you could fly through them, on some Magic School Bus, you’d find two stars at their center—two huge stars, whipping around each other once every 5.5 years. When their orbits bring them close together, as they did in August 2014, the stars are only as far apart as Mars and the sun. During that close passage, and the two previous to that, astronomers peered deep into the heart of the Homunculus Nebula to find out about the stars that supply its blood. Here’s what they’ve learned about Eta Carinae—the name given to the pair of stars—and what its massive liveliness tells us about the rest of the universe.
The big star is 90 times the mass of the sun, while the “small” star is 30 times as massive. Together, they put out as much light as 6 million copies of our star. Their gravitational tugs and intense radiation make the system, and any planets that might form there, truly different from where we live, giving scientists a window into the kind of neighborhood we’ll never inhabit.
If you moved the big star to our solar system, it would stretch beyond Earth’s orbit. (Please don’t move the big star to our solar system.) It’s so big and bright that it blinds us to what the “small” star is like. Classic sibling dynamic.
The Homunculus Nebula didn’t exist until 1840, when one of the stars exploded and ejected enough stuff to make 10 brand-new suns. But the rejected material turned into a nebula instead of 10 suns, because who needs 10 new suns? But in the distant future, after the big star goes supernova, the spewed stuff will clump together and transform into new suns.
In its 1840s glory days, Eta Carinae’s eruption made it the brightest star system in the southern hemisphere, even though it’s 7,500 light-years away. The star was so big that it survived the self-destruction that would have slayed lesser specimens. We understand these lesser specimens better than huge ones because there are many more to study, just as we understand baldness better than werewolf syndrome. Eta Carinae lets scientists watch weird scenes, like survived suicide attempts, that aren’t playing out in most cosmic theaters.
The two stars are still spewing out material, in what is called “stellar wind.” They are slowly shrinking as they lose themselves to space. Their winds smash into each other at 7 million miles per hour, heating the gas to 10 million degrees. How will this mass loss, and the catastrophic wind collision, affect their evolution and lifetime? Tune in a few hundred years from now to find out the latest.
Astronomers mixed X-ray data with Hubble observations, tracking activity over 11 years and three close encounters between the stars. Then, they threw in a (large) dash of supercomputer simulations. Out of this witch’s brew came videos showing how the cosmic-gale-force winds shape-shift as the stars pull away and come back together. It looks like an iTunes music “visualization,” in case anyone in the universe uses those anymore.
It gets one step cooler: Astronomers used a Makerbot to 3-D print the star system at various steps in its dance. Although they sit in offices all day studying Eta Carinae, they still learned new things when they could literally reach for the stars. They discovered spiky spine-like protrusions and a hidden cavity embedded in the swirling spiral. Printed 3-D models allow scientists to look at the universe inside-out and outside-in, potentially revolutionizing their ability to understand increasingly complex datasets. And also they make really cool paperweights.
A 3-D printed Eta Carinae is held in front of Hubble's images of the object. Credit: NASA's Goddard Space Flight Center/Ed Campion Astronomy is a weird science. You can’t ask the universe to magically show you a set of stars that are 5 10, 50, and 100 times as massive as the sun, all the same age and birthed in the same circumstances, so you can see how their lives differ. You have to accept the messy distribution of what’s out there, when it’s out there. You must take what the telescopes give you. Sometimes, the telescopes give the gift of Eta Carinae. And now you can give that gift, too, if you own a 3-D printer. NASA will make the files publicly available soon, so you can create your own bizarre star system and hold a 7,500-light-year-distant, 10-million-degree object in your hand. Now that’s a stellar souvenir.