LOS ANGELES, Aug. 6 (Xinhua) -- U.S. astronomers, through an orbiting telescope, have been observing an intergalactic pileup 5 billion light years from Earth, officials said Monday.

The infrared Spitzer Space Telescope, managed by the Jet Propulsion Laboratory (JPL) in Pasadena, Los Angeles, detected evidence that four galaxies are smashing into each other and eventually will merge into a single galaxy up to 10 times the size of the Milky Way, said JPL officials.

"This rare sighting provides an unprecedented look at how the most massive galaxies in the universe form," according to JPL.

The colliding galaxies were discovered by chance during a survey of a distant cluster of galaxies known as CL0958+4702. The telescope detected an unusually large fan-shaped plume of light that turned out to be billions of older stars being flung away during the collision.

Astronomers say that about half of those stars later will fall back into the galaxies, three of which are about the size of the Milky Way and the fourth about three times as big.

"When this merger is complete, this will be one of the biggest galaxies in the universe," said Kenneth Rines of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

Rines likened the cosmic collision to four sand trucks smashing together, "flinging sand everywhere."

The findings will be published in the Astrophysical Journal of Letters.