When Stars Collide
Enter Einstein's grand construct of gravitational wonders, and do not attempt to adjust your television set.
- By Trudy E. Bell
- Air & Space magazine, September 2005
Dana Berry/NASA GSFC
(Page 2 of 5)
Einstein’s theory grappled with changing gravitational fields, such as that of a massive star when it explodes and throws off most of its mass. Centuries earlier, Galileo, Kepler, and Newton had all derived equations that accurately described the behavior of gravity between ordinary objects and Earth or the mutual interaction among suns and planets in space—the equivalent of ants crawling across the checked tablecloth. But Einstein wondered exactly how objects could “sense” changes in other objects’ positions or masses across the vacuum of space. So he invented a new concept of gravity. He realized that gravity could be explained as a curvature of space-time.
Mathematic calculations show that a single object drifting in a straight line at an unchanging velocity would remain embedded in space-time, sitting at the bottom of its gravitational well, its gravitational field a static force. But an object accelerating—exploding or rotating asymmetrically—or two objects revolving around each other would cause disturbances in space-time, or gravitational waves, which would propagate outward in all directions. The more massive the object(s) and the faster the motions, the greater the deformation of space-time, and the stronger the disturbances. And if the right kinds of instruments could be built, those gravitational waves should be detectable.
Physicists do. An unambiguous sign of gravitational waves would confirm the speed and characteristics of such waves as predicted by Einstein’s general theory of relativity, which undergirds all modern physics of the very massive and the very fast.
And astronomers do. Gravitational waves carry information about extreme astronomical processes now unknowable any other way.
“All the light we see from an [exploding] star is just from individual atoms in its outer layers,” explains Lee Samuel Finn, director of the Center for Gravitational Wave Physics at Pennsylvania State University in State College. “We can’t peer into its thermonuclear engine. But gravitational waves come from its bulk matter, traveling through the outer layers without scattering, extinction, or reddening, letting us directly see the collapse of the stellar core.”
Gravitational disturbances, like light and sound, move in waves with characteristics like frequency, wavelength, and strength that can vary over time. In fact, one type of detector is trying to convert gravitational vibrations into ordinary sound.
Hum a Few Bars
“We’re like deaf people, watching other people’s lips move and trees fall. We suspect there is sound, but we have never heard it, and can only guess how to build something that can detect its vibrations,” explains Michael E. Zucker, a gravitational wave physicist who splits his time between the Massachusetts Institute of Technology and a gravitational wave detector outside Baton Rouge, Louisiana.