Astronomy Picture of the Day

Explanation: Accelerate a charge and you'll get electromagnetic radiation: light. But accelerate any mass and you'll get gravitational radiation. Light is seen all the time, but, so far, a confirmed direct detection of gravitational radiation has been elusive. When absorbed, gravitational waves create a tiny symmetric jiggle similar to squashing a rubber ball and letting go quickly. Separated detectors can be used to discern gravitational waves from everyday bumps. Powerful astronomical sources of gravitational radiation would coincidentally jiggle even detectors on opposite ends of the Earth. Pictured here are the four-kilometre-long arms of one such detector: the LIGO Hanford Observatory in Washington state, USA. Together with its sister interferometer in Louisiana, these gravitational wave detectors continue to be upgraded and are now more sensitive than ever.