|FILE PHOTO: This NASA/ESA Hubble Space Telescope image shows the bright star-forming ring that surrounds the heart of the barred spiral galaxy NGC 1097, a Seyfert galaxy. NASA/ESA/Hubble/Handout via REUTERS/File Photo|
Topics: Astrophysics, Einstein, General Relativity, Gravitational Lensing
The first observation of gravitational microlensing by a star other than the Sun has been reported by astronomers using the Hubble Space Telescope. Predicted by Albert Einstein as a consequence of his general theory of relativity, gravitational microlensing involves the gravitational field of a star bending light coming from a more distant star. It was first observed during a total eclipse in 1919 by looking for deflections in the positions of stars in parts of the sky next to the Sun. Now, Kailash Sahu of the Space Telescope Science Institute in the US and an international team have measured the gravitational lensing of a background star by a white dwarf star called Stein 2051 B. Because the background star is not lined-up perfectly with Earth and Stein 2051 B, a combination of gravitational lensing and Earth's motion around the Sun causes the background star to appear to trace out a loop around Stein 2051 B. Sahu and colleagues mapped its position at five different times in 2013-14 and used this information to calculate the mass of Stein 2051 B. It turns out that astronomers have puzzled over the mass of the white dwarf for over 100 years. It is part of a binary system and the motion of its distant companion suggests that Stein 2051 B has a smaller mass than most white dwarfs, implying that it might have an exotic composition. This recent work, however, suggests that the star has a mass expected for a white dwarf of its radius. The observations will be described in and upcoming paper in Science. 
CAPE CANAVERAL, Fla. - Astronomers have found a new application for Albert Einstein's century-old theory of relativity - using it to directly measure the size of a star beyond the sun.
In research published on Wednesday, scientists said they used the Hubble Space Telescope to plot minute changes in the path of light coming from a distant background star as it passed by a relatively close target star, known as Stein 2051B.
Researchers applied Einstein's findings to measure how Stein 2051B's gravity warped the background star's light, a phenomenon the physicist predicted more than 100 years ago and a direct means to assess its mass. The technique could be applied to other stars.
"It was like measuring the motion of a little firefly in front of a light bulb from 1,500 miles away," astronomer Kailash Sahu of the Space Telescope Science Institute in Baltimore said at a news conference.
The research was presented at a meeting of the American Astronomical Society in Austin, Texas, on Wednesday and also published in this week's issue of the journal Science. 
1. Flash Physics: Bent light reveals stellar mass, amorphous topological insulators, Tibetan Plateau rose rapidly, Sarah Tesh, Physics World
2. Einstein's theory provides new technique to size up stars, Reporting by Irene Klotz; Editing by Letitia Stein and Bill Trott, Reuters Science