The National Aeronautics and Space Administration said the nine compact galaxies discovered by the Hubble and Spitzer space telescopes are 100 to 1,000 times smaller than the Milky Way galaxy.

"These are among the lowest mass galaxies ever directly observed in the early universe," said Nor Pirzkal of the Space Telescope Science Institute in Baltimore.

Pirzkal said he was surprised to find the galaxies' estimated masses were so small. Hubble's cousin observatory, Spitzer was used to make precise determinations of their masses and confirmed the galaxies are some of the smallest yet observed.

NASA said the discovery offers insights into the universe's formative years, just 1 billion years after the Big Bang.

The galaxies were first identified by James Rhoads of Arizona State University and

NASA's Jet Propulsion Laboratory manages the Spitzer Space Telescope, while the Hubble Space Telescope is a joint project of NASA and the European Space Agency.