We are are seeing it as it existed 13.1 billion years ago, the time it has taken its light to reach us, they said.
The distance to the galaxy dubbed z8_GND_5296 -- when it emitted the light we are now seeing -- was determined by analyzing its redshift, the stretching of its light waves toward the red end of the color spectrum caused by its movement away from us.
While the 13.1-billion-year-old light traveled toward Earth the galaxy has kept moving, astronomers said, and they estimate it is now 30 billion miles away.
The astronomers said they were surprised to discover the distant galaxy is turning gas and dust into new stars at an impressive rate, hundreds of times faster than our own galaxy can.
"One very interesting way to learn about the Universe is to study these outliers and that tells us something about what sort of physical processes are dominating galaxy formation and galaxy evolution," lead researcher Steven Finkelstein from the University of Texas at Austin said.
The distant galaxy was first detected by the Hubble Space Telescope and its distance was then confirmed with observations by the ground-based Keck Observatory in Hawaii.
"What was great about this galaxy is not only is it so distant, it is also pretty exceptional," Finkelstein said.