Washington — The dazzling lights of the night sky have fascinated humankind for millennia, but new findings announced by NASA reveal that unseen objects in the universe — those seen only in infrared light — are more luminous and massive than ever believed.
The discoveries, announced August 29, were made by the Wide-field Infrared Survey Explorer (WISE), an unmanned craft launched in 2009. Instruments aboard the orbiting craft spent almost a year photographing the entire sweep of space, taking photographs every 11 seconds.
“WISE has exposed a menagerie of hidden objects,” said Hashima Hasan, a WISE program scientist at NASA headquarters in Washington.
Included in that menagerie are energy-consuming black holes, millions of them in fact, according to astronomer Daniel Stern, who studies the WISE data at NASA’s Jet Propulsion Laboratory (JPL) in California.
WISE unveiled “the jackpot of black holes, more than had been found by any previous survey,” said Stern. The WISE data is being made available to astronomers everywhere, and one study identified about 2.5 million actively feeding supermassive black holes across the full sky, some of them more than 10 billion light years away.
WISE data has helped astronomers better understand the cycle of growth and expansion within galaxies and their black holes. A black hole dubbed Sagittarius A in our Milky Way galaxy has mass 4 million times that of our sun, achieved through periodic “feeding frenzies” where material falls toward the black hole and irradiates its surroundings.
The WISE data allows researchers to spot what they think are the brightest objects ever seen, once researchers are able to see past the cosmic dust that clouds their light in the visible spectrum.
“These objects can be a thousand times more luminous than our own Milky Way galaxy,” said Peter Eisenhardt, another WISE project scientist at JPL. These powerful objects, burning with infrared light, are called hot, dust-obscured galaxies or “hot DOGs.”
NASA’s Spitzer Space Telescope followed up on the WISE findings and discovered that the hot DOGs are also home to supermassive black holes, continually consuming the material around them, at the same time new stars are being produced.
“These dusty, cataclysmically forming galaxies are so rare WISE had to scan the entire sky to find them," said Eisenhardt.
WISE data also gives astronomers new insights into the life cycle of different galaxies. The Milky Way is a spiral, disc-shaped galaxy, said Rachel Somerville, who holds the Downsbrough Chair in astrophysics at Rutgers University, while WISE sent back photographs of elliptical galaxies with a different shape and behavior.
“In spiral galaxies, the stars rotate around in a very orderly way, almost like the animals on a merry-go-round, while in the elliptical galaxies, the stars swarm around much more randomly, like a cloud of bees,” said Somerville.
Another difference between the two types of galaxies is that new stars are still forming in the spiral, disc-shaped galaxies, while only old stars are found in the elliptical galaxies, Somerville said. The different characteristics bring further fire to a dispute among astronomers about whether galaxies are formed by different processes or whether they all undergo an evolution through diverse states.
Further analysis of the WISE data and new telescopes to be launched by NASA in the near future may provide further evidence to resolve these mysteries of the universe.