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black hole star orbit

Distant black-hole-orbiting star confirms key test of Einstein’s theory of relativity

Image credit: reuters

Einstein’s theory of relativity has been proven at a massive scale, scientists have said, after analysing the movement of a star which orbits the massive black hole at the centre of our galaxy.

Researchers from the University of California studied a star called S0-2 which boasts a mass roughly 10 times larger than the Sun.

They found that the intense gravitational field emanating from the black hole was slowing the light emerging from the star as it made its way through the cosmos.

This observation is one of the best ways to test a key observation of the theory of relativity, which suggests that light will lose energy when travelling through extreme gravitational fields.

The theory of relativity is considered one of the pillars of science and explains the laws of gravity and their relation to other natural forces.

The star travels in an elliptical orbit lasting 16 years around the supermassive black hole called Sagittarius A* residing at the centre of the Milky Way 26,000 light years from Earth.

The study focused on an effect called gravitational redshift and relied heavily on data from the Keck Observatory in Hawaii, which is currently being besieged by local protestors who are trying to prevent the construction of another telescope on top of the Mauna Kea mountain.

While Einstein’s theory held up in the observations of this star, astronomer Andrea Ghez of the University of California said it may not be able to fully account for what happens in the most exotic possible gravitational environments like those of black holes. These extraordinarily dense celestial entities exert gravitational fields so strong that no matter or light can escape.

The study detected a co-mingling of space and time near the black hole as predicted by Einstein’s theory. Isaac Newton’s 17th century law of universal gravitation could not account for these observations, Ghez said.

“Newton had the best description of gravity for a long time, but it started to fray around the edges. Einstein provided a more complete theory. Today, we are seeing Einstein’s theories starting to fray around the edges,” said Ghez, who led the study published in the journal Science. At some point a more comprehensive theory of gravity may be required, she said.

Einstein’s theory foresees the wavelength of electromagnetic radiation including light lengthening as it escapes the pull of gravity exerted by a massive celestial body like a black hole.

Photons - particles of light - expend energy to escape but always travel at the speed of light, meaning the energy loss occurs through a change of electromagnetic frequency, rather than a slowing of velocity. This causes a shift to the red end of the electromagnetic spectrum, known as a gravitational redshift.

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