Credit: NASA/JPL-Caltech/T. Pyle (SSC)

This artist's conception shows what a dusty and bright galaxy located billions of light-years away might look like close up if viewed in infrared light. Galaxies like these are so far away and so drenched in dust, they appear invisible to optical telescopes.

NASA's Spitzer Space Telescope uncovered a hidden population of dusty galaxies like these using its heat-seeking infrared eyes. The galaxies are among the brightest in the universe and are located 11 billion light-years away back to a time when the universe was 3 billion years old. The universe is currently believed to be 13.5 billion years old.

Astronomers are not sure what is lighting up these cosmic behemoths, but they speculate that quasarsthe most luminous objects in the universemay be lurking inside.