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Star orbiting black hole supports Einstein’s theory
神祕恆星繞黑洞 再次驗證廣義相對論

A star known as S0-2, the blue and green object in this artist’s rendering, that made its closest approach to the supermassive black hole at the center of the Milky Way last year is shown in this US National Science Foundation image released on July 25.

Photo: Reuters

Observations of light coming from a star zipping in orbit around the humongous black hole at the center of our galaxy have provided fresh evidence backing Albert Einstein’s 1915 theory of general relativity, astronomers said on July 25.

Researchers studied a star called S0-2, boasting a mass roughly 10 times larger than the sun, as it travels in an elliptical orbit lasting 16 years around the supermassive black hole called Sagittarius A* residing at the center of the Milky Way 26,000 light years from Earth.

They found that the behavior of the star’s light as it escaped the extreme gravitational pull exerted by the black hole, with 4 million times the sun’s mass, conformed to Einstein’s theory’s predictions. The famed theoretical physicist proposed the theory, considered one of the pillars of science, to explain the laws of gravity and their relation to other natural forces.

While Einstein’s theory held up in the observations of this star, astronomer Andrea Ghez of the University of California, Los Angeles 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. And 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.


1. humongous adj.


(chao1 ju4 da4 de5)

2. elliptical adj.


(tuo3 yuan2 xing2 de5)

3. gravitational pull phr.

引力(yin3 li4)

4. account for phr.


(jie3 shi4; shuo1 ming2)

5. foresee v.

預見(yu4 jian4)

6. expend v.


(hua1 fei4; sun3 hao4)

The study, relying heavily on data from the Keck Observatory in Hawaii, focused on an effect called gravitational redshift. 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, a gravitational redshift.










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