Most Distant Gravitational Lens Helps Weigh Galaxies – But Also Deepens A Galactic Mystery
From a serendipitous discovery made with the Large Binocular Telescope, a team of astronomers led by Arjen van der Wel from the Max Planck Institute for Astronomy (MPIA) has found the most distant gravitational lens yet – a galaxy that, as predicted by Albert Einstein’s general theory of relativity, deflects and intensifies the light of an even more distant object. The discovery provides a rare opportunity to directly measure the mass of a distant galaxy. But it also poses a mystery: Lenses of this kind should be exceedingly rare. Given this and recent other finds, astronomers either have been phenomenally lucky – or, more likely, they have underestimated substantially the number of small, very young galaxies in the early universe.
Light is affected by gravity, and light passing a distant galaxy will be deflected as a result. Since the first find in 1979, numerous such gravitational lenses have been discovered. In addition to providing tests of Einstein’s theory of general relativity, gravitational lenses have proved to be valuable tools. Notably, one can determine the mass of the matter that is bending the light – including the mass of the still-enigmatic Dark Matter, which does not emit or absorb light and can only be detected via its gravity. Also, the lens magnifies the background light source, acting as a “natural telescope” that allows astronomers a more detailed look at distant galaxies than what is normally possible.