The discovery by the U.S. National Radio Astronomy Observatory's Karl G. Jansky Very Large Array instrument in New Mexico allowed them to use the unusual alignment to learn otherwise-unobtainable facts about the nearer galaxy, they said.
The more-distant galaxy, nearly 7 billion light-years from Earth but with strong radio emissions, lines up almost directly behind a closer one known as UGC 10288. In all previous images, the two galaxies had been blended together, astronomers said.
"This changed the picture, quite literally," Judith Irwin, of Queen's University in Ontario, Canada, said. "It changed our understanding of the characteristics of UGC 10288, but also gave us an unexpected new tool for learning more about that galaxy."
The alignment of a foreground galaxy with such a strongly-emitting background galaxy with extended jets probably is the first such alignment found, the astronomers said, and with its radio jets perpendicular to UGC 10288's disk it provides a valuable means of studying the nearer galaxy.
"We can use the radio waves from the background galaxy, coming through the nearer one, as a way to measure the properties of the nearer galaxy," Jayanne English, of the University of Manitoba, said.
Irwin and English worked with an international team of astronomers from North America, Europe, and India.
"We're getting a nice scientific reward from the unexpected discovery of the background galaxy," Irwin said. "Ironically, we would not have included UGC 10288 in our original study if its radio brightness had not been boosted by the background galaxy in the earlier images."