Einstein's theory provides new technique to size up stars

[June 08, 2017]  By Irene Klotz

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.

The measurements show the mass of Stein 2051B is about two-thirds of the sun in Earth's solar system. It is a type of star known as a white dwarf, which is what all stars smaller than eight times the size of the sun will become when they run out of nuclear fuel and collapse, leaving a hot core.

"The single most important thing for the star is its mass," Sahu said. "If we know the mass, we known what its radius will be, how bright it will be, how long it will live, what will happen after it dies. Everything depends on the mass of the star."

Scientists previously determined the mass of three other white dwarf stars using an indirect technique that required the star to have an orbiting partner for measuring gravitational pull.

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

The bending of light was a key test for Einstein's general theory of relativity, which was published more than 100 years ago, and proven in 1919 when scientists measured the curving of starlight around the sun during a total solar eclipse.

Einstein's work laid the foundation for modern physics and cosmology, providing a perspective of space and time that is shaped by gravity.

Sahu and colleagues are the first to observe the phenomenon in a star beyond the sun, Terry Oswalt of Embry-Riddle Aeronautical University in Daytona Beach, Florida, said in a related essay in Science.

(Reporting by Irene Klotz; Editing by Letitia Stein and Bill Trott)

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