Einstein Passes Another Test
Astronomers using NASA's Rossi X-ray Timing Explorer (RXTE)
spacecraft reported on November 6 that they have observed a black hole
that is literally dragging space and time around itself as it
rotates. This bizarre effect, called "frame dragging," is the
first evidence to support a prediction made in 1918 using
Einstein's Theory of Theory of Relativity.
The phenomenon is distorting the orbit of hot, X-ray
emitting gas near the black hole, causing the X-rays to peak at
periods that match the frame dragging predictions of general
relativity. The research team, led by Dr. Wei Cui of the
Massachusetts Institute of Technology, announced its results
in a press conference during the American Astronomical
Society's High Energy Astrophysics Division (HEAD) meeting in
Estes Park, CO. Collaborators in the research include Dr. Wan
Chen of NASA's Goddard Space Flight Center, Greenbelt, MD, and Dr.
Shuang N. Zhang of NASA's Marshall Space Flight Center,
"If our interpretation is correct, it could demonstrate the
presence of frame dragging near spinning black holes," said Cui.
"This observation is unique because Einstein's theory has never
been tested in this way before."
Black holes are very massive objects with gravitational
fields so intense that near them, nothing, not even light, can
escape their pull. This effect shrouds the hole in darkness, and
its presence can only be inferred from its effects on nearby
matter. Many of the known or suspected black holes are orbiting a
close "companion" star. The black hole's gravity pulls matter
from the companion star, which forms a disk around the black hole
as it is drawn inward by the black hole's gravity, much like soap
suds swirling around a bathtub drain. Gas in this disk gets
compressed and heated and emits radiation of various kinds,
The research team used these X-ray emissions to determine
if frame dragging was present. The team found that the X-ray
emissions were varying in intensity. By analyzing this variation,
they found a pattern, or repetition, that was best explained by a
perturbation in the matter's orbit. This perturbation, called a
precession, occurs when the orbit itself shifts around the black
hole. This is evidence for frame dragging because as the matter
orbits the black hole, the space-time that is being dragged around
the black hole drags the matter along with it. This shifts the
matter's orbit with each revolution.
Einstein's Theory of General Relativity has been highly
successful at explaining how matter and light behave in strong
gravitational fields, and has been successfully tested using a
wide variety of astrophysical observations. The frame dragging
effect was first predicted using general relativity by Austrian
physicists Joseph Lense and Hans Thirring in 1918. Known as the
Lense-Thirring effect, it has not been definitively observed thus
far, so scientists will scrutinize the new reports very carefully.
The possible detection of frame dragging around another
type of very dense, rapidly spinning object called a neutron
star was accomplished recently by Italian astronomers, Drs. Luigi Stella
of the Astronomical Observatory of Rome, and Mario Vietri of the Third
University of Rome. Their observations were also made using the RXTE,
which is available for use by astronomers throughout the world, and led
Dr. Cui's team to seek the effect near black holes.
"This is exciting work that needs further confirmation, as
for any seemingly major advance in science," said Dr. Alan Bunner,
Director of the Structure and Evolution of the Universe Program at
NASA Headquarters, Washington, DC.
The RXTE spacecraft is a 6,700 pound observatory placed
into orbit by NASA in December 1995. Its mission is to make
astronomical observations from high-energy light in the X-ray
range, which is emitted by powerful events in the Universe. These
events are often associated with massive, compact objects such as
black holes and neutron stars.