Magazine article Science News

General Relativity Caught in Action: Debris Disk around Black Hole Shows Frame-Dragging Effect

Magazine article Science News

General Relativity Caught in Action: Debris Disk around Black Hole Shows Frame-Dragging Effect

Article excerpt

An effect of general relativity that is barely measurable on Earth has been spotted in full force around a black hole.

Physicists detected the signature of a black hole twisting the fabric of spacetime around it. The discovery, reported December 16, is the best evidence yet of this effect, known as frame dragging, around a black hole.

Scientists detected the extreme frame dragging by analyzing a disk of star debris swirling around a black hole about 28,000 light-years away. X-rays from the disk suggest that its matter is on a wild ride as the spacetime it occupies gets yanked and warped by the spinning black hole.

Albert Einstein's century-old general theory of relativity describes gravity in terms of massive objects deforming the surrounding spacetime. For example, Earth creates a dent in spacetime much like a bowling ball would on a rubber sheet. Frame dragging is less intuitive: It stipulates that if the ball were spinning, it would drag the sheet along with it.

Physicists with the Gravity Probe B satellite measured Earth-induced frame dragging using gyroscopes (57V: 12/26/15, p. 7). Absent relativity's effects, the axis of each gyroscope's spin would have pointed in the same direction forever. But the axes deviated by about a hundred-thousandth of a degree per year due to Earth's rotation. The experiment required extreme sensitivity to capture such a subtle effect.

But frame dragging should be anything but subtle around a black hole, which packs an immense mass within a small volume. …

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