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Cosmic Test Upholds Einstein’s Theory Of General Relativity

April 25, 2013
Image Caption: This artist’s impression shows the exotic double object that consists of a tiny, but very heavy neutron star that spins 25 times each second, orbited every two and a half hours by a white dwarf star. The neutron star is a pulsar named PSR J0348+0432 that is giving off radio waves that can be picked up on Earth by radio telescopes. Although this unusual pair is very interesting in its own right it is also a unique laboratory for testing the limits of physical theories. This system is radiating gravitational radiation, ripples in spacetime. Although these waves cannot be yet detected directly by astronomers on Earth they can be detected indirectly by measuring the change in the orbit of the system as it loses energy. As the pulsar is so small the relative sizes of the two objects are not drawn to scale. Credit: ESO/L. Calçada

Lee Rannals for redOrbit.com — Your Universe Online

Astronomers have found a way to test Einstein’s theory of gravity in ways that were not possible before now, thanks to new observations of a very unique system.

A team used telescopes around the world to study the most massive neutron star confirmed so far, orbited by a white dwarf. The scientists wrote in the journal Science that so far the new observations match up with Einstein’s predictions for general relativity.

Einstein’s general theory of relativity explains gravity as a consequence of the curvature of space-time created by the presence of mass and energy. This theory has withstood all tests and was first published nearly a century ago.

The researchers discovered an exotic double object that included a tiny, but heavy neutron star that spins 25 times a second. This star is being orbited every two and a half hours by a white dwarf. This rapidly rotating neutron star, known as a pulsar, gives off a distinct radio signal detectable on Earth giving the team a unique laboratory to test the limits of physical theories.

The pulsar, PSR J0348+0432, is twice as heavy as the Sun, but only 12-miles across. The gravity at its surface is more than 300 billion times stronger than what we experience on Earth, and its packed full of matter in its center with over one billion tons for every sugar-cube-sized scoop.

“I was observing the system with ESO´s Very Large Telescope, looking for changes in the light emitted from the white dwarf caused by its motion around the pulsar,” says John Antoniadis, a PhD student at the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn and lead author of the paper. “A quick on-the-spot analysis made me realize that the pulsar was quite a heavyweight. It is twice the mass of the Sun, making it the most massive neutron star that we know of and also an excellent laboratory for fundamental physics.”

Until now, astronomers had no idea what would happen in the presence of a massive neutron like PSR J0348+0432. This neutron star offers a unique opportunity to test out general relativity theories. The close proximity between the white dwarf and pulsar leads to the production of gravitational waves as the gap between the two objects shrinks over time. There are competing formulations of general relativity that predict how such a system would evolve over time, so measurements of the system´s motion will reveal which versions of the theory are flawed.

“Our radio observations were so precise that we have already been able to measure a change in the orbital period of 8 millionths of a second per year, exactly what Einstein´s theory predicts,” Paulo Freire, another team member on the project, said in a statement.

This work is just the beginning of what astronomers will be doing with this pair. Scientists will be using this unique opportunity to continue to test general relativity to even greater precision over time.

Another group of scientists from several universities helped to affirm Einstein’s theory, as well as the existence of dark matter, back in 2010. This team analyzed over 70,000 galaxies at least 3.5 billion light years away from Earth. After calculating the clustering of these galaxies and analyzing their velocities and distortion from intervening material, the team showed that the theory explains the nearby universe better than alternative theories of gravity.


Source: Lee Rannals for redOrbit.com – Your Universe Online



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