Stunning 3-D Models Reveal Bizarre Double Star Acting Up

The star system Eta Carinae sends out the brightest flares yet recorded.
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The supermassive star pair Eta Carinae erupted in the 1840s and produced this double-lobed cloud of dust called the Homunculus Nebula.


SEATTLE—Armed with a 3-D printer, a supercomputer, and several space telescopes, astronomers have gotten their best look yet at one of the galaxy's biggest, weirdest double star systems.

Surprising new observations of the system, known as Eta Carinae, described Wednesday at the American Astronomical Society's annual winter meeting, include a set of oddly bright flares that might signal a change in the two stars' billowing stellar winds. What's more, 3-D printed simulations show unexpected anatomy within the star system's churning, tempestuous center.

Scientists have kept a close eye on Eta Carinae since the 1840s, when a series of unexpected eruptions briefly transformed it into the brightest star in the southern sky. At any time, the unstable system could explode in a spectacular supernova. (Don't worry—Earth will be fine. But the light show will be unforgettable.)

The new observations don't pin down when Eta Carinae might explode, but they are helping astronomers better understand the turbulent pair.

"It's not only the most massive and luminous object that's close to us, but it's also extremely erratic," says astronomer Michael Corcoran of NASA's Goddard Space Flight Center, in Greenbelt, Maryland.

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Scientists used a 3-D printer to build models that show the interacting winds of the dual-star system Eta Carinae. When the two stars near each other, newly identified spine-like protrusions form along a cavity created in the primary star's wind.


Sibling Rivalry

It looks like a single point of light in the constellation Carina, but Eta Carinae (7,500 light-years away) is actually the violent, unstable product of two giant stars, one big and one smaller, whirling around each other. The smaller star, a relatively puny 30 solar masses, escaped notice until 1996. The primary star is at least 90 times more massive than the sun, and five million times brighter.

"As a result of this extreme luminosity, the stars are basically blowing themselves apart," Corcoran says.

Supercomputer simulations show the stellar winds of Eta Carinae, a star system that's the most luminous and massive within 10,000 light-years of Earth. Red and yellow show higher wind density.  NASA'S GODDARD SPACE FLIGHT CENTER/T. MADURA

Every 5.5 years, the smaller star completes a slingshot-like orbit around the bigger star, and at their closest the two snuggle in as near as Mars is to the sun.

Whenever the stars get close, odd things happen. Each star generates violent stellar winds blowing between one million and six million miles (1.6 million and 9.6 million kilometers) per hour, and when these winds collide, they heat the surrounding gas and produce high-energy X-rays.

"You can imagine a six-million-mile-per-hour object smacking in and decelerating to zero quite rapidly—that would generate a lot of energy," Corcoran says.

For the past 18 years, astronomers have used orbiting space telescopes like NASA's Swift satellite to measure the X-rays produced when the stars are closest together. The last time this happened, in August, the X-rays were the brightest on record.

Scientists don't know precisely why the 2014 X-rays were unusually bright, but Corcoran suggests it had something to do with the winds produced by the smaller star, which might be losing more mass and blowing denser winds.

NASA detectors show pulses of X-rays from 1998 to 2014, with the biggest blast in 2014.  NASA'S GODDARD SPACE FLIGHT CENTER/M. CORCORAN

Bright Future

Because Eta Carinae hides behind a thick, dusty nebula, it's hard for astronomers to see the stars. Instead, they simulated the stars' closest pass using the Pleiades supercomputer at NASA's Ames Research Center, in California.

Scientists then fed the result—a beautiful spiraling pattern in the wake of the stars' closest approach—into a 3-D printer. The 3-D printout, which is bright orange and about the size of a large Nerf ball, revealed a surprise: bulbous, finger-like protrusions radiating from the spiral, which scientists now have to explain.

"These are features that we didn't even know really existed," says Thomas Madura, an astrophysicist at NASA's Goddard Space Flight Center. "We think these are real physical features that arise due to physical instabilities."

Scientists converted a supercomputer’s simulations of Eta Carinae's winds into a 3-D digital model, which revealed unexpected spine-like protrusions (left) in the environment around the two stars, three months after their closest passage.  NASA GODDARD CI LAB

It isn't the first time Eta Carinae has puzzled astronomers. When it erupted in the 1840s, it was the brightest star in the southern sky for several years. Then it dimmed to normal, almost as if nothing had happened. (Read more about how scientists are studying the star's 1840s outbursts.)

But something had indeed happened. The event, termed the Great Eruption, left the star shrouded in the huge, dusty, double-lobed Homunculus Nebula. The eruption ejected as much as ten solar masses of material from the double star system—and to this day, astronomers aren't sure which of the two stars actually did the erupting.

Or when it will erupt again. If it explodes in a supernova, it could be visible in the daytime sky, says astrophysicist Theodore Gull of NASA's Goddard Spaceflight Center. The flash could be comparable in brightness to the moon, he says.

And when will that be? It seems to be very stable right now, Gull says. In reality, "we have no clue."

Follow Nadia Drake at National Geographic's Phenomena blog, No Place Like Home, and on Twitter.

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