Kepler Data Shows Light-bending Gravity In Action
April 5, 2013

NASA’s Kepler Observes Light-bending Gravity In Binary Star System

[ Watch the Video: Dead Star Warps Light of Red Star ]

redOrbit Staff & Wire Reports - Your Universe Online

NASA's Kepler space telescope has observed the effects of a dead star bending the light of its companion star, one of the first detections of this phenomenon in double star systems.

The dead star, known as a white dwarf, is the burnt-out core of what used to be a star much like our sun. It is locked in an orbiting pattern with its partner, a small "red dwarf" star, which is physically larger than the tiny white dwarf but has less mass.

"This white dwarf is about the size of Earth but has the mass of the sun," said Phil Muirhead of the California Institute of Technology, Pasadena, and lead author of the findings.

"It's so hefty that the red dwarf, though larger in physical size, is circling around the white dwarf."

Kepler's primary mission is to scan the universe for orbiting planets. As the planets pass by, they block the starlight by miniscule amounts, which Kepler's sensitive detectors can see.

"The technique is equivalent to spotting a flea on a light bulb 3,000 miles away, roughly the distance from Los Angeles to New York City," said study co-author Avi Shporer, also of Caltech.

Muirhead and colleagues routinely use public Kepler data to search for and confirm planets around smaller stars, the red dwarfs. Also known as M dwarfs, these stars are cooler and redder than our sun.

When the astronomers first looked at the Kepler data for a target called KOI-256, they thought they were looking at a huge gas giant planet eclipsing the red dwarf.

"We saw what appeared to be huge dips in the light from the star, and suspected it was from a giant planet, roughly the size of Jupiter, passing in front," Muirhead said.

To learn more about the binary star system, Muirhead and his colleagues turned to the Hale Telescope at Palomar Observatory near San Diego. Using a technique known as radial velocity, they discovered that the red dwarf was wobbling around like a spinning top, but with a wobble far too large to be caused by the tug of a planet.

That´s when they knew they were witnessing a massive white dwarf passing behind the red dwarf, rather than a gas giant passing in front.

The team also used ultraviolet measurements of KOI-256 obtained by the Galaxy Evolution Explorer (GALEX), a NASA space telescope now operated by the California Institute of Technology in Pasadena.

The GALEX is part of an ongoing program to measure ultraviolet activity in all the stars within Kepler´s view, an indicator of potential habitability for planets in the systems.

The GALEX data revealed the red dwarf is very active, consistent with being "spun-up" by the orbit of the more massive white dwarf.

The scientists then went back to the Kepler data and noticed that when the white dwarf passed in front of its star, its gravity caused the starlight to bend and brighten by measurable effects -- an element of Einstein´s general theory of relativity.

"Only Kepler could detect this tiny, tiny effect," said Doug Hudgins, the Kepler program scientist at NASA Headquarters, Washington.

"But with this detection, we are witnessing Einstein's general theory of relativity at play in a far-flung star system."

One of the consequences of Einstein's general theory of relativity is that gravity bends light. Astronomers regularly observe this phenomenon, often called gravitational lensing, in our galaxy and beyond. It has been helpful in studying dark matter, dark energy and ancient star-forming galaxies.

Gravitational lensing has also been used to discover new planets and search for free-floating planets.

In the current study, scientists used gravitational lensing to determine the mass of the white dwarf, and were able to combine this information with the other data they acquired to accurately measure the mass of the red dwarf and the physical sizes of both stars.

The findings will be published April 20 in the Astrophysical Journal.