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Relativity rules star near our galaxy’s black hole

A 26-year-long observational campaign provides clear evidence of the effect that general relativity has on the motion of a star known as S2 as it boomerangs around the supermassive black hole at the center of our Milky Way galaxy.

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LIGO witnesses another black hole crash

Image: Gravitational waves
An artist’s conception shows gravitational waves emanating like ripples in space time as two black holes approach each other in their orbits. (Credit: T. Pyle / LIGO)

t looks as if gravitational-wave watchers are in for a bumpy, beautiful ride. Scientists using the Laser Interferometer Gravitational-Wave Observatory, or LIGO, have confirmed the detection of another merger involving two faraway black holes.

The observations, which were made last Christmas and reported today in a paper published by Physical Review Letters, support the idea that LIGO could open up a whole new branch of astronomy focusing on gravitational disturbances and black holes.

“It is a promising start to mapping the populations of black holes in our universe,” Gabriela Gonzalez, a Louisiana State University astrophysicist who serves as the spokesperson for the LIGO Scientific Collaboration, said in a news release.

She and her colleagues say this smash-up was smaller than the first black-hole merger, which was observed in September and reported by the LIGO team in February. That clash involved black holes that were 29 and 36 times as massive as the sun. This one brought together black holes that were eight and 14 times the sun’s mass.

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LISA Pathfinder blazes trail to test relativity

Image: LISA Pathfinder liftoff
The LISA Pathfinder probe lifts off from French Guiana. (ESA photo)

The LISA Pathfinder probe is heading for a vantage point a million miles from Earth to help look for gravitational waves and add a missing piece to the evidence for general relativity.

The European Space Agency said an Italian-built Vega rocket sent the spacecraft into low Earth orbit from ESA’s spaceport on the South American coast, at Kourou in French Guiana, at 04:04 GMT today (8:04 p.m. PT Wednesday).

Over the next two weeks, LISA Pathfinder will go through a series of maneuvers to set a course for L1, a gravitational balance point between Earth and the sun. The spacecraft is due to reach L1 in mid-February and begin its scientific mission in March.

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General relativity gets a 100th birthday party

Image: Albert Einstein
Albert Einstein works at the blackboard during a lecture in Vienna in 1921. (F. Schmutzer via Wikipedia)

This week’s 100th anniversary of Albert Einstein’s general theory of relativity is a geeky cause for celebration, but what’s arguably the concept’s toughest test has just gotten under way.

General relativity was a follow-up to special relativity, Einstein’s big idea from a decade earlier. Back in 1905, he worked out a way to explain why the speed of light is constant, regardless of an observer’s point of view: It’s because space and time are not inflexible metrics, but interrelated dimensions that are measured differently depending on your perspective.

Special relativity explained a lot of the weirdness that physicists were puzzling over at the time, but the theory applied only to “special” conditions that didn’t involve acceleration – for example, how things fall in a gravitational field. On Nov. 25, 1915, Einstein laid out how the interplay of space and time gives rise to gravity and the fabric of the cosmos.

The theory passed its first big test in 1919, when observations during a total solar eclipse were found to be more consistent with Einstein’s view of gravity than with Isaac Newton’s. General relativity has been passing tests ever since. For example, if we didn’t take relativistic effects into account, our GPS readings would seem out of whack.

This week is prime time for centennial retrospectives on the theory and its implications. Here are a few to keep you entertained.

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