Complex sentence: In April 2015, astronomers announced the discovery of a supervoid, the largest known structure in the universe, 1.8 billion ly (550 Mpc) across ad characterized by its unusual emptiness.
Split into simpler sentences: In April 2015, astronomers announced the discovery of a supervoid, the largest known structure in the universe. This big hole is 1.8 billion ly (550 Mpc) across, characterized by its unusual emptiness.