"We expected that there should be this large population of hidden quasars in the universe, but WISE can now identify them across the sky," Stern said. "We think these quasars are really important for shaping how galaxies look today."
In addition to this haul of gorging black holes, WISE has turned up a smaller population of rarer objects researchers are dubbing "hot DOGs," for hot, dust-obscured galaxies.
These galaxies are thought to be extremely bright, but appear very faint to us because their light is shrouded by dust.
"It is actually the most obscured objects in the WISE sky that are among the brightest objects in the universe," said Peter Eisenhardt, a WISE project scientist at JPL. "They're definitely a different type of beast than we’ve seen before."
The hot DOGs observed by WISE number about 1,000, and are mostly spotted from very far away, meaning they existed in the early days of the universe, because their light has taken billions of years to travel to Earth.
Scientists suspect these weird objects may represent a missing link in galaxy evolution, capturing a brief phase in the life of a galaxy that is transitioning from being a spiral disk galaxy like our milky way to what's called an elliptical galaxy.
Astronomers used to think spirals and ellipticals were two wholly separate classes of galaxy, but now researchers are coming to believe they are just two different stages of life. A merger between two colliding galaxies, or some other dynamic process, may transform a spiral into an elliptical.
And that halfway point between the two could perhaps be embodied by hot DOGs, scientists speculate.
"We think we may be seeing these galaxies at a crucial transformational stage," said Rachel Somerville, an astrophysicist at Rutgers University. The Milky Way itself could someday become a hot DOG, she said, after it collides with our neighbor Andromeda, which it is expected to do in about 2 billion years.