Hubble confirms another Einstein prediction

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Astronomers were able to see, for the first time, the light of a star different from the sun, deformed by the gravitational force of a nearby object

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Astrophysicists have been able to confirm , thanks to the Hubble Space Telescope, a corollary of Albert Einstein ‘s theory of general relativity enunciated more than a century ago, which was thought to be impossible to obtain direct observation in distant stars .

These astronomers were able to see, for the first time, the light of a star different from the sun, deformed by the gravitational force of an object passing by.

This phenomenon, called “gravitational lens effect”, opens a new window on the history and evolution of galaxies such as ours, the Milky Way, according to the scientists, whose observations were published Wednesday.

“Einstein would be proud,” said Terry Oswalt, a professor of physics at the University of Aeronautics at Embry Riddle in Maryland,” and one of its key forecasts has successfully passed a rigorous test of observation.

The effect of gravitational lens was first observed in 1919 when, during a total eclipse, the light the sun deformed and took the form of a circle.

“When an object passes exactly between us and a star, this lens effect forms a perfect circle of light called the Einstein ring,” explained Professor Oswalt.

This observation was then the first convincing proof of Albert Einstein’s theory of general relativity, according to which gravity is fundamental force acting on space and time.

However, Einstein considered that this effect was impossible to observe in other stars since they were too far from each other.

In an article published in 1936 in the same journal Science, the German physicist wrote “that for this reason (the distance between stars) there was no hope of being able to see this phenomenon directly.”

Einstein then could not anticipate the appearance of the Hubble telescope in 2009, which revolutionized astronomy by allowing observation of stars and galaxies far away.

With the help of Hubble , the team led by Kailash Sahu of Baltimore’s Space Telescope Science Institute observed the light of a distant star diverted by a white dwarf, “Stein 2051-B” .

A white dwarf is a star that has exhausted its hydrogen but is still massive despite its small size.

A new tool

At least 97% of the stars that exist and have existed in our galaxy, including the sun, are or will become white dwarfs, which tells us both about our future and our past, experts say.

The amplitude of the deviation of light from a star depends directly on the mass and gravity exerted by the white dwarf.

The mass of Stein 2051-B represents about two-thirds of the mass of the sun.

During this last observation, Professor Sahu and his team realized that the star and the dwarf Stein 2051-B were not fully aligned, which explained that the Einstein circle formed by the deviated light was asymmetric, Mass of the white dwarf.

For Professor Oswalt, this observation is important because “it seeks a new tool to determine the mass of celestial objects, difficult to calculate otherwise.”

This research “also solves an ancient mystery about the mass and composition of the white dwarf Stein 2051-B,” he says.

Oswalt added that “Professor Sahu’s team also confirmed the findings of Indian astrophysicist Subrahmanyan Chandrasekhar, Nobel Prize for Physics in 1983, for his theory on the relationship between mass and radius of white dwarfs.”

Thanks to this gravitational lens effect, astronomers were able to announce in 2016 to have observed for the first time four simultaneous images of a very distant supernova.

In the case of this supernova, an end-of-life star that exploded more than 9 billion years ago, the mass of surrounding galaxies had strongly deformed space- time and diverted light.
Source: AFP

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