Scientists Prepare to Place Einstein on the Rim of a Black Hole

Cambridge, MA - It may soon be sink-or-swim time for Albert Einstein. Scientists are preparing for the ultimate test of Einstein's law of gravity, known as the theory of general relativity, through a systematic, in-depth study of hundreds of black holes.

But there are really no losers in this exam. The observations will either strengthen Einstein's legacy or reveal flaws in general relativity that eventually will pave the road to a more complete theory. Dr. Jon Miller of the Harvard-Smithsonian Center for Astrophysics discusses the potential for testing Einstein at a meeting held this week at Stanford University entitled "Beyond Einstein: From The Big Bang to Black Holes."

The goal is to study the effect of gravity on time, matter and energy where gravity is most pronounced: at the theoretical border of a black hole called the event horizon. Scientists know where to look, and now they are building the tools needed to do it.

"For extreme gravity, you can't beat a black hole," said Miller. "Current observations take us close to a black hole, where we see glimpses of the bizarre physics predicted by Einstein. In a few more years, with a next-generation X-ray telescope, we will be able to zoom in closer yet, right to the event horizon, to give Einstein a proper testing."

One proposed mission that could do this, Miller said, is the Constellation X-ray Observatory. This observatory comprises four satellites flying and observing in unison, with a combined light-collecting area 100 times larger than any X-ray mission before it.

Many of Einstein's predictions have been confirmed: observations reveal that gravity can bend light, slow time and warp space-time. Scientists hope to go one step further to find whether gravity causes such effects to the precise degree that Einstein's math predicts. To answer this question, far more detailed knowledge about black holes is needed. The workhorses of X-ray astronomy -- NASA's Chandra X-ray Observatory and Rossi X-ray Timing Explorer and Europe's XMM-Newton Observatory - have provided tantalizing hints that Einstein is right, but nothing yet is conclusive.

The pursuit to understand gravity to such precision is far from trivial, Miller said. General relativity and quantum mechanics were the physics behind nearly every scientific advance of the twentieth century, from nuclear energy to computers. General relativity evolved from cracks in Newton's 225-year-old gravity law. Could it be that cracks in general relativity will usher in the next great scientific revolution? Scientists say that something isn't quite right -- either general relativity, quantum theory, or both -- because neither theory can describe all of the forces in the universe.

Scientists will look for small deviations between observation and theory in black hole measurements. This is not without precedent: about 100 years ago, astronomers found that the measured orbit of Mercury around the Sun differed from what was predicted by Isaac Newton's law of gravity by about 70 miles per year. Albert Einstein's law of gravity, general relativity, accounts for the discrepancy, which is caused by a subtle warp in space-time from the Sun's gravity speeding Mercury's orbit. Clearly, precise measurements were needed to uncover the deviation.

Fast-forward to the 21st century: Miller said that Constellation-X will be so efficient at detecting distorted light from black hole systems that scientists will be able to build libraries of light profiles, from which it will be possible to test predictions of gravitational light bending around black holes. This is because Constellation-X will detect more light in less time, allowing scientists to create "movies" in a single observation of the movement of matter as it approaches a black hole event horizon. Constellation-X also will dramatically reveal how black holes, which have no surface, can spin like a tornado in space, dragging the fabric of space (space-time) along with it.

Constellation-X is a key mission in NASA's Beyond Einstein roadmap. For more information, refer to http://constellation.gsfc.nasa.gov or http://universe.nasa.gov. For more information on the Beyond Einstein meeting, refer to http://www-conf.slac.stanford.edu/einstein/.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7462 Fax: 617-495-7468
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
cpulliam@cfa.harvard.edu