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In a new test of Einstein's theory of gravitation, a group of astronomers from the Netherlands, the United States, Australia, and Canada demonstrated that the theory holds , even for a triple stellar system. Their work is published in the journal Nature .
An artist impression of the triple PSR star system J0337 + 1715, which is located about 4,200 light-years away from the Earth. Image credit: NRAO / AUI / NSF / S. Dagnello
Einstein's gravity theory states that all objects fall in the same way despite their mass or composition, like a cannonball and an apple falling from the leaning tower To date, Einstein's equations have passed all tests, from minute laboratory studies to observations of planets in our solar system.
But alternatives to his theory predict that compact objects with extremely high gravity, such as neutrons, stars fall a little differently from objects of lesser mass. This difference would be due to the so-called gravitational bonding energy of a compact object – the gravitational energy that holds it together.
In 2011, astronomers discovered a natural laboratory to test the theory of Einstein in extreme conditions – PSR J0337 + 1715 three-star system in which a binary composed of a millisecond radio pulsar and d & rsquo; A white dwarf in a 1.6-day orbit is itself in a 327-day orbit with another white dwarf
"PSR J0337 + 1715 is a unique star system, we do not know it not others like that, making it a unique laboratory to test Einstein's theories, "said Dr. Ryan Lynch, an Observatory astronomer of the Green Bank in West Virginia
White dwarfs are very dense stars, whereas their size is comparable to that of the Earth, their mass is similar to that of our Sun.
Neutron stars are even smaller and denser than white dwarfs. of collapsed star cores that have suffered supernova explosions and are the densest stars in the universe.
Many neutron stars are pulsars, emitting regular electromagnetic signals at the lighthouse scale. "We can explain each pulse of the neutron star in PSR J0337 + 1715 since we started our observations," said team leader Dr. Anne Archibald of the University. Amsterdam and the Netherlands Radio Astronomy Institute.
"We can say its location a few hundred meters away.This is a very accurate track of where the neutron star was and where it goes."
Si the alternatives to Einstein's gravitational image were correct, then the neutron star and the inner white dwarf in the PSR J0337 + 1715 would fall "The inner white dwarf is not as massive or compact than the neutron star, and therefore has less gravitational binding energy, "said Dr. Scott Ransom, an astronomer of the National Radio Astronomy. Observatory
Through careful observations and calculations, the researchers were able to test the severity of the system using the pulses of the neutron star alone
They found that any difference in acceleration between the neutron star and the white dwarf
"there is a difference, it is not more than three parts in a million," said Dr. Nina Gusinskaia, member of The University of Amsterdam Team
"Now, Someone with an Alternative The theory of gravitation has an even narrower range of possibilities in which their theory has to be s & # 39; 39, insert, to match what we have seen. "
" Whenever we have tested Einstein's theory of relativity, the results have "We continue to look for deviations from relativity because it could help us understand how to describe gravity and how quantum mechanics with the same mathematical language, "says Ingrid Stairs, a professor at the University of British Columbia.
The result of the team is 10 times more accurate than the previous best test of gravity, which makes the proof of Einstein's Strong Equivalence Principle much stronger
"We are still looking for better measurements in new places, so our quest to learn to know new frontiers in our Universe will continue, "said Dr. Ransom.
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Anne M. Archibald and others . 2018. Universality of the free fall of the orbital motion of a pulsar in a triple stellar system. Nature 559: 73-76; doi: 10.1038 / s41586-018-0265-1
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