Using galaxies as giant magnifying lenses, researchers have measured the size and age of the Universe, giving strength to the gravitational lensing technique as one that can provide reliable data on the parameters of the Universe.

Gravitational lensing uses a large nearby object such as a galaxy to magnify a distant object, perhaps another galaxy. The light from the background galaxy detours around the foreground galaxy, 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.

"In our case, there were four copies of the source, which appear as a ring of light around the gravitational lens," says lead author of the study Sherry Suyu, from the University of Bonn. Suyu and colleagues studied the B1608+656 system, using data collected by the Hubble Space Telescope and the Wilkinson Microwave Anisotropy Probe (WMAP).

By looking at the arrival times of each of the four light sources, the scientists could extract information about the distances travelled and the density of the lens galaxy. Likening it to a traffic jam in a busy city, Marshall says: "The traffic density in a big city is like the mass density in a lens galaxy. If you take a longer route, it need not lead to a longer delay time. Sometimes the shorter distance is actually slower."

The scientists measured the distance to the distant galaxy to infer the overall scale of the Universe, often expressed as Hubble's Constant, confirming the age of the Universe as 13.75 billion years old to within 170 million years.

Moreover, the measurements provided an equally precise measurement of Hubble's constant as long-established tools such as the observation of supernovae and the cosmic microwave background, providing an increase in precision of more than a factor of two compared with previous work on this galactic system.

"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). "Gravitational lensing has come of age as a competitive tool in the astrophysicist's toolkit."

The results are published in the 1 March issue of The Astrophysical Journal.

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