University Communications

Winter 1998
Rising Star
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The black hole has not, of course, been Ghez's only major find. It's just her most recent. Using the same "infrared speckle interferometry" technique she, in 1993, found that contrary to prior assumptions, most stars form with a twin, located at distances smaller than that of our solar system. Theories on star formation have typically been based on single-star systems such as our own, despite the fact that in our solar neighborhood, about half of the middle-aged stars have companions. Many astronomers believed that these stars had begun solo and then, by the process of capture, had become binary later in life.

Ghez used her technique to look at young stars, anticipating she would find either no binaries -- meaning the capture theory was correct -- or the same proportion found in middle-aged stars, suggesting companions emerge in the process of star formation. Instead, she found twice as many companions in the younger stars.

"When you look at a stellar nursery, you see almost all binary stars, and when you see the middle-aged stars like our sun, about half of them are in binary star systems. So there's a discrepancy," Ghez says. "There are two models, I think, to possibly explain it. Either all of these systems form as multiple systems and then fall apart by the time they get to the age of our sun, or some systems just form stars more efficiently than others."

The reverberations of her discovery were immediate: For one thing, "this suggests there might not be as many planets as one might otherwise think," Ghez observes, since the gravity of twin suns likely would unhinge the neat ring of stardust from which planets are formed.

"Most of these stars are actually separated by the distance between our sun and just inside of, say, Pluto. So they are very close. And the second star is going to disrupt the gas and dust, so I think it's unlikely that the very closest binary systems are capable of forming stable planetary systems," she says.

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