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and general relativity is confirmed, again and again and again....
Einstein always wins
Science 18 January 2008:
Vol. 319. no. 5861, p. 271
DOI: 10.1126/science.319.5861.271a
Einstein always wins
Science 18 January 2008:
Vol. 319. no. 5861, p. 271
DOI: 10.1126/science.319.5861.271a
News of the Week
ASTRONOMY:
Most-Massive Black Hole Confirms Relativity Rules the Universe
Govert Schilling*
AUSTIN, TEXAS--You can run from Einstein, but you can't hide. Astronomers observing a supermassive black hole 3.5 billion light-years from Earth have found that the object brightened dramatically at just the time the equations of general relativity predicted. As a bonus, scientists pegged the black hole's mass at a staggering 18 billion times the mass of the sun, six times as big as the previous record holder.
"This is a pretty spectacular extension of the regime in which the effects of relativity have been measured," says theoretical physicist Robbert Dijkgraaf of the University of Amsterdam, the Netherlands, who was not involved in the study. It's also bad news for proposed alternative theories of gravity that give slightly different predictions, Dijkgraaf says.
The supermassive black hole, known as OJ287, resides in the core of a distant galaxy, where its gravity sucks in matter from an enormous disk of gas and dust rotating around it. As the matter plunges toward the black hole, the galaxy's core turns into a glowing energy furnace. Twenty years ago, astronomers sifting through photographs dating back to 1891 discovered that every 12 years or so, the radiation from this accretion disk flares up to about 100,000 times normal, in two bursts just over a year apart (see figure).
To astronomers, such periodic behavior smacked of orbital motion. Mauri J. Valtonen of the University of Turku in Finland proposed that a smaller companion goes around the supermassive black hole, following a very elongated orbit strongly tilted with respect to the primary's accretion disk. Every 12 years, at its closest approach, the smaller black hole passes through the accretion disk twice, stirring it up and heating nearby matter enough to produce a brightness peak. After new flares appeared in 1994, 1995, and November 2005, Valtonen and colleagues modeled the binary's orbit and predicted that the next peak would occur on 13 September 2007.
About 30 professional and amateur observatories, including the German 3.5-meter telescope at Calar Alto Observatory in Spain and the 2.5-meter Nordic Optical Telescope on the Canary Island of La Palma, joined forces to check the forecast. At the 211th meeting of the American Astronomical Society held here last week, Valtonen proudly presented the results: The flare showed up as predicted, beautifully confirming the binary model. From the orbital motion, the researchers calculated the masses of the two black holes to be 18 billion solar masses for the primary and a more modest 100 million suns for the companion.
The observations also marked yet another triumph for Einstein's theory of general relativity, which states that the extremely strong gravitational field near the supermassive black hole should distort spacetime in ways that rapidly change the orientation of the companion's orbit. It also predicts that the loss of energy from the emission of gravitational waves should cause the orbit to shrink--an effect that won a 1993 Nobel Prize for two physicists who first detected it in a binary neutron star. Without spacetime curvature, the flare would have occurred 10 days earlier than predicted, Valtonen says; without gravitational waves, 20 days later.
"The result is of fundamental importance, since precision measurements that really test general relativity only became available quite recently," Dijkgraaf says. On a cosmic time scale, this particular test case will be gone soon as well: The two black holes are expected to collide and merge within some 10,000 years. When that happens, astronomers will really have something to stare at.
Govert Schilling is an astronomy writer in Amersfoort, the Netherlands.
ASTRONOMY:
Most-Massive Black Hole Confirms Relativity Rules the Universe
Govert Schilling*
AUSTIN, TEXAS--You can run from Einstein, but you can't hide. Astronomers observing a supermassive black hole 3.5 billion light-years from Earth have found that the object brightened dramatically at just the time the equations of general relativity predicted. As a bonus, scientists pegged the black hole's mass at a staggering 18 billion times the mass of the sun, six times as big as the previous record holder.
"This is a pretty spectacular extension of the regime in which the effects of relativity have been measured," says theoretical physicist Robbert Dijkgraaf of the University of Amsterdam, the Netherlands, who was not involved in the study. It's also bad news for proposed alternative theories of gravity that give slightly different predictions, Dijkgraaf says.
The supermassive black hole, known as OJ287, resides in the core of a distant galaxy, where its gravity sucks in matter from an enormous disk of gas and dust rotating around it. As the matter plunges toward the black hole, the galaxy's core turns into a glowing energy furnace. Twenty years ago, astronomers sifting through photographs dating back to 1891 discovered that every 12 years or so, the radiation from this accretion disk flares up to about 100,000 times normal, in two bursts just over a year apart (see figure).
To astronomers, such periodic behavior smacked of orbital motion. Mauri J. Valtonen of the University of Turku in Finland proposed that a smaller companion goes around the supermassive black hole, following a very elongated orbit strongly tilted with respect to the primary's accretion disk. Every 12 years, at its closest approach, the smaller black hole passes through the accretion disk twice, stirring it up and heating nearby matter enough to produce a brightness peak. After new flares appeared in 1994, 1995, and November 2005, Valtonen and colleagues modeled the binary's orbit and predicted that the next peak would occur on 13 September 2007.
About 30 professional and amateur observatories, including the German 3.5-meter telescope at Calar Alto Observatory in Spain and the 2.5-meter Nordic Optical Telescope on the Canary Island of La Palma, joined forces to check the forecast. At the 211th meeting of the American Astronomical Society held here last week, Valtonen proudly presented the results: The flare showed up as predicted, beautifully confirming the binary model. From the orbital motion, the researchers calculated the masses of the two black holes to be 18 billion solar masses for the primary and a more modest 100 million suns for the companion.
The observations also marked yet another triumph for Einstein's theory of general relativity, which states that the extremely strong gravitational field near the supermassive black hole should distort spacetime in ways that rapidly change the orientation of the companion's orbit. It also predicts that the loss of energy from the emission of gravitational waves should cause the orbit to shrink--an effect that won a 1993 Nobel Prize for two physicists who first detected it in a binary neutron star. Without spacetime curvature, the flare would have occurred 10 days earlier than predicted, Valtonen says; without gravitational waves, 20 days later.
"The result is of fundamental importance, since precision measurements that really test general relativity only became available quite recently," Dijkgraaf says. On a cosmic time scale, this particular test case will be gone soon as well: The two black holes are expected to collide and merge within some 10,000 years. When that happens, astronomers will really have something to stare at.
Govert Schilling is an astronomy writer in Amersfoort, the Netherlands.