An international team of astronomers has recently announced a finding that helps to settle a long-standing debate over the relationship between mass (the amount of matter) and luminosity (brightness) in galaxies.

The team achieved this result by compiling the largest-ever single collection of 'gravitational lens' galaxies - 70 in all. A gravitational lens is a phenomenon similar to a terrestrial mirage, but it occurs on a scale of many thousands of light-years.

When two galaxies happen to be precisely aligned with one another in the sky, the gravitational field of the nearer galaxy distorts the image of the more distant galaxy into multiple arc-shaped images or even into a complete ring, known as an 'Einstein ring'. These Einstein ring images can be up to 30 times brighter than the image of the distant galaxy would be in the absence of the lensing effect.

By Dr A Bolton