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If you drop a bowling ball and a baseball in a large building, you can usually expect them to fall and hit the ground at the same time.
Even under conditions of extreme gravity, very different from the scale of physics we know of on Earth, gravity affects objects in the same way – as Albert Einstein had predicted .
This allowed us to go beyond what is possible in the solar system. – Ingrid Stairs, University of British Columbia
Thus finds the most extreme test of a key principle of gravity of the general theory of Einstein. Relativity calls for the principle of strong equivalence, which states that all objects fall in the same way in the same gravity.
Other theories of gravity have suggested that the principle might not apply in cases of extreme gravity.
Such "zombie stars" are sometimes left behind after a massive star explodes into a supernova. The material collapses into a core so dense that a teaspoon weighs as much as Mount Everest.
The study was led by Canadian astronomer Anne Archibald, originally from Montreal but now a postdoctoral researcher at the Netherlands Institute. But a study conducted by Canadian astronomer Anne Archibald, a postdoctoral researcher at the Netherlands Radio Astronomy Institute, allowed to take very precise measurements of a neutron star called "pulsar" towards the radio astronomy. another star. The researchers compared this to measurements of a much clearer white dwarf star (with only one fifth of the sun's mass) falling to the same star, and found no measurable difference in their response to the gravity of the star. Said Ingrid Stairs, a professor of astronomy at the University of British Columbia, who co-authored the study, published today in Nature.
Einstein's theory describes gravity as: a curvature in the space-time that objects follow when they "fall". In space, the fall due to gravity can be seen as stars, planets and moons in orbit around another.
The William E. Gordon Telescope in Arecibo, Puerto Rico, was one of three radio telescopes used to measure pulsar pulses. . (Arecibo Observatory)
"In Einstein's theory, the Earth or a bowl of petunias or a whale, or any other object should do exactly the same thing," Archibald said. . " No matter what they are made of or how big they are."
Of course, the idea that gravity is caused by a curvature in space – time is pretty weird. That's one of the reasons people have been trying to find other theories of gravity, Archibald said. Many have been proven wrong, but some have not yet done so. Some of them, called scalar-tensor theories, predict that objects will not behave according to Einstein's theory under conditions of extreme gravity.
This new experience does not completely refute these theories but makes them much less likely.
Rare trio
What made this test possible is the discovery of a trio of rare and unique stars by Stairs and some colleagues in 2012 – a special type of 39; neutron star orbiting a system of triple stars
The neutron star observed in this study is a millisecond pulsar, a neutron star that rotates very rapidly – 366 times per second. that case. Like a beacon that emits a flashing light beam when it is spinning, the pulsar emits a radio beam that strikes the Earth as a series of impulses. This pulsar speed is rare – most run at less than one-tenth of that speed.
Albert Einstein's general theory of relativity says that gravity is a curvature in space-time and predicts that all objects will fall in the same way in a gravitational field, regardless of their mass or what they are made of . Canadian Press Photo Archive)
But what is even rarer, is a pulsar in orbit with two other stars – and a smaller white dwarf circle, because a slightly larger white dwarf orbits them two. While "living" stars are often found in trios, neighboring stars generally do not survive the massive explosion that generates a neutron star.
"For a triple system to survive a supernova that forms a pulsar, right away," says Stairs, the researchers realized that this system, called PSR J0337 + 1715 and located at about 2,400 light-years away in the constellation Taurus, could be used for a gravity test.
"This allowed us to go beyond what is possible in the solar system," said Stairs. "We were very excited by that."
Researchers could compare the effect of gravity of the outer white dwarf on the two inner stars of very different masses.
To do this, they measured pulsar pulses using three radio telescopes on Earth, and Archibald, Stairs and several collaborators, including researchers in the Netherlands, Australia and the United States, spent 1,200 hours remote telescopes from their computers to collect measurements.
They analyzed the moment of each impulse to follow the movement of the pulsar. The more frequent the pulses, the more precise the measurements. Finally, they sought changes in the orbit of the pulsar and the inner white dwarf corresponding to the movement and gravity of the outer white dwarf.
Nestor Ortiz, formerly of the Perimeter Institute in Waterloo, Ontario, and now a researcher postdoctoral fellow at the University of Jena in Germany, worked on the theories of gravity gravity. In an email to CBC News, he agreed that the study excludes a little more than other alternative theories of gravity. He added that the study does not prove that general relativity is "the" correct theory of gravity and "there is still plenty of room" for other theories to survive.
Sanjeev Seahra, professor at the University of New Brunswick who is interested in the alternative theories of gravitation and quantum mechanics that explain black energy, such as those mentioned in the study, described his findings as "exciting result".
" What intrigues this result is that the authors actually measured a small deviation from the general relativity, but the data was not good enough to say s & # 39; 39, it was a true signature of alternative gravity or a stroke of statistical luck. "" I look forward to following up to solve this problem. "
The new study was funded by the Netherlands Foundation for Scientific Research, the European Research Council, the Australian Research Council, the Canadian Institute for Advanced Research, the Natural Sciences and Engineering Research Council of Canada and the National Science Foundation of the United States.
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