Glowing blue arches stretching across 1.9 million trillion miles of space are really only optical illusions created when gravity bends light, astronomers said.
The discovery that the arches are mirages suggests that the universe contains so much "dark matter" invisible from Earth that the universe eventually might collapse under its own gravity in another "big bang" instead of expanding forever, Stanford University astronomy Chairman Vahe Petrosian said.
Last January, Petrosian and astronomer Roger Lynds of Kitt Peak National Observatory near Tucson, Ariz., announced their baffling discovery of two and possibly three arches, or arcs.
One arc appeared to stretch 1.9 million trillion miles through a cluster of galaxies named Abell 370, which is about 7 billion light years, or 41 billion trillion miles, from Earth--twice as far as announced in January. Another appeared in galaxy cluster 2244-02, and there were faint signs of a third arc in cluster Abell 2218. Galaxies contain billions of stars.
The National Optical Astronomy Observatories, which operates Kitt Peak, announced in January that the arcs were "the largest optically visible structures yet observed in the universe."