It has already been possible to measure the mass of a white dwarf star, thus proving a particular type of “gravitational lens” already predicted more than a hundred years ago by physicist Albert Einstein in the theory of general relativity.
And the theory says that when the light of a distant star passes through a body that is aligned and closest to us, we can see gravity deforming the so-called “fabric” of the cosmos and causing the brightness that is emitted in the distance, draw a curve in space. This is a simplified description of the complex phenomenon of the “gravitational lens” predicted a century ago in Albert Einstein’s theory of general relativity. In an article published this week in the journal Science, an international team of scientists reported that it was able to confirm for the first time a particular type of this effect on a small star located outside our solar system.
There is thus another window open to study small objects that emit little light and which we could not reach.
One of the special occurrences of the gravitational lens effect is that in which two stars (one further from us and one closer) are perfectly aligned and form one hoop of light on each other. At this high point of the gravitational effect is given the name of “Einstein ring”.
A hundred years ago, the physicist already knew that everything was happening like this, that is to say, the gravitational effect was proven very early. During the observations of the eclipse in 1918 everything was confirmed. Still, Einstein’s ring took some more time to observe.
In an old paper published in Science in 1936, Albert Einstein pointed out that the long distance separating us from the stars robbed any hope of observing this phenomenon directly. By then Einstein was correct.
The advance of the technology that allowed the creation of powerful telescopes, happened a hundred years ago, in the year of 1988, was there that, for the first time, the ring of Einstein was observed.
Now with the images taken by the Hubble telescope, an international team of astrophysicists led by Kailash C. Sahu of the Space Telescope Institute (USA) used this effect (the gravitational lens with the ring) to accurately measure the mass of A little white dwarf star. Although they are the majority in our galaxy, white dwarfs are stars that are at the end of their life cycle (as one day, approximately as 4500 million years from now) will happen to our Sun, are small and already emit little light, which makes them almost inaccessible to scientists.
Kailash C. Sahu’s team came up to them.
The scientists began by looking for stars that could cross each other in a possible alignment to generate an Einstein ring and pointed the Hubble to a white dwarf named Stein 205b. This white dwarf was about 17 light-years away from us and crossed with another distant star (five thousand light-years) between October 2013 and October 2015.
There, the stars were slightly misaligned and formed an asymmetric ring, which facilitated difficult observations and measurements. As the Nature magazine reports on this article, the distance we are dealing with in these scenarios will be comparable to putting a person in London looking at an ant crossing a coin in Moscow.
“Using a slightly misaligned ring, scientists have been able to measure the position of the farthest star and calculate with extreme precision the mass of the star [white dwarf]that acts as a lens”, explained Ricardo Reis of the Communication Group at the Institute of Astrophysics and Space Sciences, adding that this observation opened new opportunities to study these small objects that emit little light.
“The calculation of mass will be something like weighing a star”, he explained.
With the images of the Hubble telescope and the asymmetric “ring” of Einstein generated around Stein 205b, the team calculated that the white dwarf star will have about 68% of the mass of the Sun. “Einstein would be proud. One of his important predictions has passed a very rigorous observation test, “said Terry Oswald, an astronomer of dwarf stars at Embry-Ridge University’s Aeronautics University in Florida, who was invited by Science to comment on the article Signed by Kailash C. Sahu.
Terry Oswald also argues that this work “provides a new tool for determining masses of objects that we cannot easily measure by other means” and was the first to observe this effect on a star other than the Sun. The astronomer added that the team Kailash C.
Sahu also confirmed “the theory that deserved the Nobel Prize in 1930, attributed to Subrahmanyan Chandrasekhar, on the relation between the mass and the ray of the white dwarf stars”.
“We now know that Stein 2051 B is perfectly normal, not a massive white dwarf with an exotic composition, as was thought”.