Astronomers use galaxies as lenses

Posted by Sraff writer

Peering through entire galaxies as their lenses, a team of researchers has found a new way to establish the size and age of the universe.

They used a technique called gravitational lensing to measure the distances light traveled from a bright, active galaxy to the earth along different paths.

"We've known for a long time that lensing is capable of making a physical measurement of Hubble's constant," says Phil Marshall of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC). Hubble's constant indicates the size and age of the universe.

However, gravitational lensing has never before been used in such a precise way. "Gravitational lensing has come of age as a competitive tool in the astrophysicist's toolkit," says Marshall.

When a large nearby object, such as a galaxy, blocks a distant object, such as another galaxy, the light can detour around the blockage. But instead of taking a single path, light can bend around the object in one of two or four different routes, thus doubling or quadrupling the amount of information scientists receive.

Lead author on the study Sherry Suyu, from the University of Bonn, said, "In our case, there were four copies of the source, which appear as a ring of light around the gravitational lens."

In the past, this method of distance estimation was plagued by errors, but physicists now believe it is comparable with other measurement methods. With this technique, the researchers have come up with a more accurate lensing-based value for Hubble's constant, and a better estimation of its uncertainty.