 |
|
In Unique Stellar Laboratory, Einstein's Theory Passes Strict, New Test
July 07, 2008Taking advantage of a unique cosmic configuration, astronomers have measured an effect predicted by Albert Einstein's theory of General Relativity in the extremely strong gravity of a pair of superdense neutron stars. Essentially, the famed physicist's 93-year-old theory passed yet another test.
Scientists at McGill University used the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT) to do a four-year study of a double-star system unlike any other known in the Universe. The system is a pair of neutron stars, both of which are seen as pulsars that emit lighthouse-like beams of radio waves.
"Of about 1700 known pulsars, this is the only case in which two pulsars orbit around each other," said Rene Breton, a graduate student at McGill University in Montreal, Canada. In addition, the stars' orbital plane is aligned nearly perfectly with their line of sight to the Earth. This causes the signal of one to be blocked, or eclipsed, as it circles the other.
"Those eclipses are the key to making a measurement that could never be done before," Breton said.
Einstein's 1915 theory predicted that in a close system of two very massive objects, such as neutron stars, one object's gravitational tug, along with an effect of its spinning around its axis, should cause the spin axis of the other to wobble, or precess.
Studies of other pulsars in binary systems had indicated that such wobbling occurred, but could not produce precise measurements of the amount of wobbling.
"Measuring the amount of wobbling is what tests the details of Einstein's theory and gives a benchmark that any alternative gravitational theories must meet," said Scott Ransom of the National Radio Astronomy Observatory.
The eclipses allowed the astronomers to pin down the geometry of the double-pulsar system and track changes in the orientation of the spin axis of one of them. As one pulsar's spin axis slowly moved, the pattern of signal blockages as the other passed behind it also changed. The signal from the pulsar in back is absorbed by the ionized gas in the other's magnetosphere.
Pulsars, first discovered in 1967, are the "corpses" of massive stars that have exploded as supernovae. What is left after the explosion is a superdense neutron star that packs more than the mass of our Sun into the size of an average city. Beams of radio waves stream outward from the poles of the star's intense magnetic field and sweep around as the star rotates, as often as hundreds of times a second.
The pair of pulsars studied with the GBT is about 1,700 light-years from Earth. The average distance between the two is only about twice the distance from the Earth to the Moon. The two orbit each other in just under two and a half hours.
"A system like this, with two very massive objects very close to each other, is precisely the kind of extreme "cosmic laboratory" needed to test Einstein's prediction," said Victoria Kaspi, leader of McGill University's Pulsar Group. Theories of gravity don't differ significantly in "ordinary" regions of space such as our own Solar System. In regions of extremely strong gravity fields, such as near a pair of close, massive objects, however, differences are expected to show up.
In the binary-pulsar study, General Relativity "passed the test" provided by such an extreme environment, the scientists said.
"It's not quite right to say that we have now 'proven' General Relativity," Breton said. "However, so far, Einstein's theory has passed all the tests that have been conducted, including ours."
Breton, Kaspi and Ransom worked with Michael Kramer of the Jodrell Bank Observatory at the University of Manchester in Great Britain; Maura McLaughlin of West Virginia University and the NRAO; Maxim Lyutikov of Purdue University and other colleagues in Canada, the U.S., France and Italy. The researchers presented their work in an article in the July 4 issue of Science Magazine.
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
The National Science Foundation (NSF)
"Those eclipses are the key to making a measurement that could never be done before," Breton said.
Einstein's 1915 theory predicted that in a close system of two very massive objects, such as neutron stars, one object's gravitational tug, along with an effect of its spinning around its axis, should cause the spin axis of the other to wobble, or precess.
Studies of other pulsars in binary systems had indicated that such wobbling occurred, but could not produce precise measurements of the amount of wobbling.
"Measuring the amount of wobbling is what tests the details of Einstein's theory and gives a benchmark that any alternative gravitational theories must meet," said Scott Ransom of the National Radio Astronomy Observatory.
The eclipses allowed the astronomers to pin down the geometry of the double-pulsar system and track changes in the orientation of the spin axis of one of them. As one pulsar's spin axis slowly moved, the pattern of signal blockages as the other passed behind it also changed. The signal from the pulsar in back is absorbed by the ionized gas in the other's magnetosphere.
Pulsars, first discovered in 1967, are the "corpses" of massive stars that have exploded as supernovae. What is left after the explosion is a superdense neutron star that packs more than the mass of our Sun into the size of an average city. Beams of radio waves stream outward from the poles of the star's intense magnetic field and sweep around as the star rotates, as often as hundreds of times a second.
The pair of pulsars studied with the GBT is about 1,700 light-years from Earth. The average distance between the two is only about twice the distance from the Earth to the Moon. The two orbit each other in just under two and a half hours.
"A system like this, with two very massive objects very close to each other, is precisely the kind of extreme "cosmic laboratory" needed to test Einstein's prediction," said Victoria Kaspi, leader of McGill University's Pulsar Group. Theories of gravity don't differ significantly in "ordinary" regions of space such as our own Solar System. In regions of extremely strong gravity fields, such as near a pair of close, massive objects, however, differences are expected to show up.
In the binary-pulsar study, General Relativity "passed the test" provided by such an extreme environment, the scientists said.
"It's not quite right to say that we have now 'proven' General Relativity," Breton said. "However, so far, Einstein's theory has passed all the tests that have been conducted, including ours."
Breton, Kaspi and Ransom worked with Michael Kramer of the Jodrell Bank Observatory at the University of Manchester in Great Britain; Maura McLaughlin of West Virginia University and the NRAO; Maxim Lyutikov of Purdue University and other colleagues in Canada, the U.S., France and Italy. The researchers presented their work in an article in the July 4 issue of Science Magazine.
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
The National Science Foundation (NSF)
General Relativity Current Events and General Relativity News RSSNew research field promises radical advances in optical technologies
A new research field called transformation optics may usher in a host of radical advances including a cloak of invisibility and ultra-powerful microscopes and computers by harnessing nanotechnology and "metamaterials."
Hubble finds large sample of very distant galaxies
New Hubble Space Telescope observations of six spectacular galaxy clusters acting as gravitational lenses have given significant insights into the early stages of the Universe. Scientists have found the largest sample of very distant galaxies seen to date: ten promising candidates thought to lie at a distance of 13 billion light-years (~redshift 7.5).
Black holes have simple feeding habits
The biggest black holes may feed just like the smallest ones, according to data from NASA's Chandra X-ray Observatory and ground-based telescopes. This discovery supports the implication of Einstein's relativity theory that black holes of all sizes have similar properties, and will be useful for predicting the properties of a conjectured new class of black holes.
RIT Team Simulates First Merger of Three Black Holes on a Supercomputer
The same team of astrophysicists that cracked the computer code simulating two black holes crashing and merging together has now, for the first time, caused a three-black-hole collision.
UO plays key role in LIGO's new view of a cosmic event
An international team of physicists, including University of Oregon scientists, has concluded that last February's intense burst of gamma rays possibly coming from the Andromeda Galaxy lacked a gravitational wave. That absence, they say, rules out an initial interpretation that the burst came from merging neutron stars or black holes within Andromeda.
Freshly painted Arecibo Observatory returns to work, spies object associated with meteor showers
After receiving its first fresh, full coat of paint in more than 40 years, Arecibo Observatory made its first observation in more than six months at 6:36 a.m., Saturday, Dec. 8.
Texas A&M researchers examine Einstein's theories on the universe
Einstein's self-proclaimed "biggest blunder" - his postulation of a cosmological constant (a force that opposes gravity and keeps the universe from collapsing) - may not be such a blunder after all, according to the research of an international team of scientists that includes two Texas A&M University researchers.
Collaboration shines possible light on objects 'weirder than black holes'
Researchers from Duke University and the University of Cambridge think there is a way to determine whether some black holes are not actually black.
Neutron stars warp space-time, U-M astronomers observe
Einstein's predicted distortion of space-time occurs around neutron stars, University of Michigan astronomers and others have observed.
MU Physicist Says Testing Technique for Gravitomagnetic Field is Ineffective
Albert Einstein's theory of general relativity has fascinated physicists and generated debate about the origin of the universe and the structure of objects like black holes and complex stars called quasars.
More General Relativity Current Events and General Relativity News Articles
 | A First Course in General Relativity by Bernard F. Schutz General relativity has become one of the central pillars of theoretical physics, with important applications in both astrophysics and high-energy particle physics, and no modern theoretical physicist's education should be regarded as complete without some study of the subject. This textbook, based on the author's own undergraduate teaching, develops general relativity and its associated... |
 | Relativity: The Special and the General Theory, The Masterpiece Science Edition, by Albert Einstein From the Commentary by Robert Geroch (The corresponding section of Einstein’s text can be found below the comment. Please note that in the book, the Commentary is placed after the complete text of Relativity.) Section 17. Space-Time Minkowski’s viewpoint represents a "geometrization" of relativity. These ideas have, over the years, come to the forefront: They reflect the perspective... |
 | General Relativity: An Introduction for Physicists by M. P. Hobson, G. P. Efstathiou, A. N. Lasenby After reviewing the basic concept of general relativity, this introduction discusses its mathematical background, including the necessary tools of tensor calculus and differential geometry. These tools are used to develop the topic of special relativity and to discuss electromagnetism in Minkowski spacetime. Gravitation as spacetime curvature is introduced and the field equations of general... |
 | General Relativity by Robert M. Wald "Wald's book is clearly the first textbook on general relativity with a totally modern point of view; and it succeeds very well where others are only partially successful. The book includes full discussions of many problems of current interest which are not treated in any extant book, and all these matters are considered with perception and understanding."--S. Chandrasekhar "A tour de force:... |
 | Gravity from the Ground Up: An Introductory Guide to Gravity and General Relativity by Bernard Schutz This book provides an accessible introduction to astronomy and general relativity, aiming to explain the Universe, not just to describe it. Written by an expert in relativity who is known for his clearly-written advanced textbooks, the treatment uses only high-school level mathematics, supplemented by optional computer programs, to explain the laws of physics governing gravity from Galileo and... |
 | General Relativity and the Einstein Equations (Oxford Mathematical Monographs) by Yvonne Choquet-Bruhat General Relativity has passed all experimental and observational tests to model the motion of isolated bodies with strong gravitational fields, though the mathematical and numerical study of these motions is still in its infancy. It is believed that General Relativity models our cosmos, with a manifold of dimensions possibly greater than four and debatable topology opening a vast field of... |
 | General Theory of Relativity by P. A.M. Dirac Einstein's general theory of relativity requires a curved space for the description of the physical world. If one wishes to go beyond superficial discussions of the physical relations involved, one needs to set up precise equations for handling curved space. The well-established mathematical technique that accomplishes this is clearly described in this classic book by Nobel Laureate P.A.M. Dirac.... |
 | Gravity, Black Holes, and the Very Early Universe: An Introduction to General Relativity and Cosmology by Tai L. Chow Chow introduces the mathematical methods essential to understanding and applying general relativity--tensor calculus, some differential geometry, etc.--but leaves to more advanced references derivations that a beginning student would likely find overly long and tedious. The book employs standard tensor analysis--which requires only basic calculus for its understanding--and resists the temptation... |
 | Gravity: An Introduction to Einstein's General Relativity by James B. Hartle The aim of this groundbreaking new text is to bring general relativity into the undergraduate curriculum and make this fundamental theory accessible to all physics majors. Using a "physics first" approach to the subject, renowned relativist James B. Hartle provides a fluent and accessible introduction that uses a minimum of new mathematics and is illustrated with a wealth of exciting... |
 | Spacetime and Geometry: An Introduction to General Relativity by Sean Carroll Spacetime and Geometry: An Introduction to General Relativity provides a lucid and thoroughly modern introduction to general relativity. With an accessible and lively writing style, it introduces modern techniques to what can often be a formal and intimidating subject. Readers are led from the physics of flat spacetime (special relativity), through the intricacies of differential geometry and... |
| © 2009 BrightSurf.com |