Hubble Space Telescope imaging of the gravitational lens ESO325-G004. Source: NASA, ESA, Hubble Heritage Team (STScI / AURA).

The Theory of General Relativity (GR) outlined by Albert Einstein in 1915 has been tested precisely within our solar system, but it has been difficult to test GR on the scale of an individual galaxy. An international team of researchers has now validated the theory on a galactic scale by combining data from NASA's Hubble Space Telescope and the European Southern Observatory's Very Large Telescope.

The researchers analyzed a nearby gravitational lens system in which light from a distant galaxy (the source) is bent by a foreground galaxy (the lens). Mass distribution in the lens was compared with the curvature of space-time around the lens, independently determined from the distorted image of the source. The result supports GR and eliminates some alternative theories of gravity.

The precise extrasolar test of GR focused on the galaxy ESO325-G004, which is one of the closest lenses at 500 million light years from Earth.

Astronomers from the University of Portsmouth (UK), the University of Cambridge (UK), the University of Durham (UK), the University of California–Santa Cruz, Haverford College (Penn.) and the Max Planck Institute for Astronomy (Germany) contributed to this research.