December 3, 1997
Rotating Black Hole Drags Space-Time
A New Test of Einstein's General Theory of Relativity
Artist's concept of the warping of space-time in the vicinity of a rotating black hole. The space-time coordinate grid (blue lines) is superimposed upon the image of a black hole. The black hole is surrounded by an accretion disk (yellow). Two high-speed jets are ejected in opposite directions from the inner part of the accretion disk.
If the black hole were non-rotating, the space-time coordinate grid would converge symmetrically toward the black hole. Due to the black hole's rotation, the grid is twisted. Only two dimensions of space-time are represented. In reality, there are four dimensions: time and three spatial coordinates.
Image Credit: Joe Bergeron of Sky & Telescope magazine.
Rotating black holes not only warp space-time in their vicinities, they also twist space-time in a spiral fashion as illustrated graphically in the above image. This is what a research team led by Dr. Wei Cui of the Massachusetts Institute of Technology confirmed by studying the intensity of X-rays emitted from an accretion disk of matter orbiting a rotating black hole.
Using NASA's Rossi X-Ray Timing Explorer (RXTE), Dr. Cui and his team found that the intensity of the X-rays varies in a way that one expects if the rotating black hole drags space-time around with it. This dragging was predicted in 1918 by two Austrian physicists, Joseph Lense and Hans Thirring, based on Einstein's general theory of relativity. The effect is called "frame dragging."
Frame dragging is expected to occur not just in the vicinity of rotating black holes. The effect should exist in the vicinity of any rotating body. However, in the case of the Sun, the Earth, and other rotating celestial objects with relatively weak gravity, frame dragging would distort space-time very little and be very difficult to detect. Only in the vicinity of objects with extreme gravity, such as rotating black holes or neutron stars, does frame dragging have a pronounced effect.
If confirmed by additional observations and experiments, frame dragging will be the fourth affirmative test of Einstein's general theory of relativity. The others are the procession of the orbits of planets and binary stars; the deflection of light by the Sun, other stars, and galaxies (e.g., gravitational lensing); and the shifting toward longer wavelengths of light as it climbs out of the gravitational wells of planets, stars, and other celestial objects.
More Cool Stuff
- For more information on Dr. Cui's and his team's discovery, see NASA press release 97-258 (November 6, 1997):
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ftp://ftp.hq.nasa.gov/pub/pao/pressrel/1997/97-258.txt
- We obtained the above image from Sky & Telescope, a popular astronomy magazine that will have an article on rotating black holes in its December issue:
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http://www.skypub.com/s_t/s_t.shtml
- The Rossi X-Ray Timing Explorer homepage is at:
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http://heasarc.gsfc.nasa.gov/0/docs/xte/XTE.html
- Early in the next millennium, NASA and Stanford University will launch a relativity gyroscope experiment into Earth orbit that will test both the warping of space-time in Earth's vicinity and frame dragging. The experiment is call Gravity Probe B:
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http://stugyro.stanford.edu/RELATIVITY/GPB/GPB.html
- We have covered the subject of black holes and gravitational lensing before in our Observations of the Week:
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http://observe.ivv.nasa.gov/nasa/ootw/1997/ootw_970319/ob970319.html
- http://observe.ivv.nasa.gov/nasa/ootw/1997/ootw_970128/ob970128.html
- http://observe.ivv.nasa.gov/nasa/ootw/1996/ootw_960327/ob960327.html
- http://observe.ivv.nasa.gov/nasa/ootw/1996/ootw_960110/ob960110.html
- http://observe.ivv.nasa.gov/nasa/ootw/1997/ootw_970128/ob970128.html