For the first time, scientists have directly detected gravitational waves, and ripples in space-time in addition to light from the spectacular collision of two neutron stars the first time that a cosmic event has been viewed in both gravitational waves and light. The discovery was made using the U.S.-based laser interferometer gravitational wave observatory (LIGO) Europe's best Virgo detector and some 70 ground and space-based observatories. Neutron stars are the smallest, densest stars known to exist and are formed when massive stars explode in supernovas as these neutron stars spiral together, the emitted gravitational waves that a)_____ for about 100 seconds when they collide a b)..... light in the form of gamma rays was emitted and seen on earth about two seconds after the gravitational waves in the days and weeks following the smashup, Aadhar forms of light or electromagnetic radiation c)..... Including x-ray ultraviolet optical infrared and radio waves are detected the observations have given astronomers a d)..... the opportunity to probe a collision of neutron stars for example observations made by the U.S Gemini Observatory the European very large telescope and the Hubble speech telescope e) signatures of recently sanitized material including gold and platinum. Solving A decade-long mystery of her about half of all elements heavier than iron are produced. The LIGO - Virgo f) and the astronomical unity have been either submitted or respected for publication in various journals.

What will be the right word in (a) of the passage?