Illustration of a binary black hole system

Grazing galaxies, imaged by Hubble Space Telesope

New technologies are helping astronomers unlock the mysteries of our Milky Way galaxy and the billions of other galaxies in our universe.

They've learned that the history of galaxies includes some violent episodes. Are elliptical, or oval, galaxies the result of cataclysmic collisions between smaller spiral galaxies? There is mounting observational evidence to support this model of galactic evolution, and the Space Interferometery Mission will search for another vital clue. With its ultra-precise measuring capabilities, the mission will peer into the very core of elliptical galaxies.

What scientists will look for at the heart of these sprawling stellar metropolises are paired systems known as binary black holes. Scientists believe many spiral galaxies contain one central black hole. An observation of two orbiting black holes would present further evidence that some elliptical galaxies are the result of galactic mergers.

The term "black hole" describes a region of space where the pull of gravity is so strong that nothing, not even light, can escape. Scientists speculate that supermassive black holes reside at the center of most galaxies, including our own Milky Way galaxy.

If two spiral galaxies were to merge into a single galaxy, their respective black holes would tend to sink toward the center and either merge or form a binary system.

The Space Interferometry Mission, scheduled to launch in 2009, will look for the to-and-fro sway that would indicate a binary system at work. This will be achieved by measuring the target's position relative to other astronomical objects. It's the same technique that the mission will use to search for small planets orbiting nearby stars.

The mission will combine light from multiple telescopes to create a giant "virtual telescope" of unprecedented resolution. To look for binary black holes, it will zero in on a point called the photocenter, the center of light emission from a cosmic source. In the case of a binary system, the photocenter is a moving target. (Animation )

The discovery of binary black holes may also provide insight into the origin of supermassive black holes, said Dr. Ann Wehrle, an astronomer at Caltech's Interferometry Science Center and principal investigator in the project. When galaxies collide, separate black holes may combine and merge at the center, gathering new mass.

Wehrle said she has long been fascinated by black holes because they embody the most extreme conditions in the known universe. Jets of matter somehow shoot out along the poles at nearly light speed, and space-time is warped in a manner predicted by Einstein's Theory of General Relativity.

Near a black hole, time slows down. At its center, matter becomes infinitely compressed, and space and time as we know it collapse.

"Black holes in the centers of galaxies are extremely massive. They are regions where the most extreme physics occurs, and things behave in ways that go against intuition," Wehrle said.

As Wehrle and other scientists continue their studies, they hope to unlock more of the secrets of these enormous, powerful, violent entities.