colliding_winds_020108 WASHINGTON D.C. - A pair of stars some 4,500 light-years from Earth engage in a titan battle every few years, when their odd orbits bring them so close they can practically smell each others' breath.
The tactics are full of bluster. The battleground is dusty. And the weaker star loses every time.
The two stars orbit one another in what astronomers call a binary arrangement. The orbits are elliptical; though they stray far from each other, they also come to within three times the distance of Earth to the Sun.
All the while the stars -- like all stars -- expel parts of themselves into space. The so-called stellar winds they generate are loaded with atomic particles.
During close orbital skirmishes every eight years, the relatively empty space between the stars is compressed so much by the battling breezes that the few atoms which are there are forced together and made into dust. The dust needs somewhere to go, so it follows the path of least resistance, rushing back toward the less powerful star.
But the weaker star is heroic. It resists the attack with its own wind, albeit a less might blow. So the dust wraps around the weaker star and is blown into open space, somewhat in the way air goes around a fist stuck out a car window, said John Monnier of the Harvard-Smithsonian Center for Astrophysics.
Monnier and NASA's William Danchi presented their scenario here yesterday at a meeting of the American Astronomical Society. Peter Tuthill of the University of Sydney also worked on the observations.
Animated star war
The physics of such a gusty star war have been understood for a decade. But only in recent years, with the help of the large Keck telescope in Hawaii and some optical tricks of the trade, could the details be seen.
By blocking out all but the outer edges of the telescope's light-gathering capabilities, the researchers created what they call an
interferometer, which lessens the blurring effects of Earth's atmosphere. Then they ran the results through a computer program, finally achieving the equivalent of seeing headlights on a car in Rome from a vantage point in California, Danchi said.By watching the battle over time, researchers detailed the dust's movement.
The result is an animation, in infrared light, showing an arc of dust expanding into space.
"We can see the dust forming in the boundary region between the colliding stellar winds and being blow away at 6 million miles per hour," Monnier said.
For comparison, the worst hurricanes on Earth typically top out at around 140 mph.
The binary system is called WR 140. The mightier combatant is a Wolf-Rayet star, an aged thing that has lost its clothing of hydrogen and is naked to its surroundings. As if to compensate for their exposed state, Wolf-Rayet stars burn hot -- more than four times as hot as our Sun and 100,000 times as bright. Its younger, weaker opponent is a garden-variety object called an 0-star.
It all might seem a terrible mismatch, but there's a surprise in store for the Wolf-Rayet star. After winning many battles, it will lose the war. In about 100,000 years, it will have expended so much energy it will simply explode.
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