WISE Embarks on 'Crazy' Blazar Hunt
Deep in the furthest-most recesses of the cosmos, a mysterious class of object is generating a lot of energy. So much energy is being generated that, as seen from Earth, these objects throb with high-energy gamma-rays.
Until recently, astronomers had little clue as to what could be generating this type of radiation. Now, as it is known that the majority of galaxies contain supermassive black holes in their cores, a possible gamma-ray “engine” has been found. These engines are known as “blazars,” and NASA has an unlikely tool to help astronomers hunt them down.
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Using data from the Wide-field Infrared Survey Explorer (WISE), 200 blazars have been identified and NASA hopes the mission will help to find thousands more.
But blazars generate gamma-rays; WISE is an infrared telescope — the mission is more accustomed to looking for cool objects like brown dwarfs, comets, asteroids and nebulae; not the hottest, most energetic sources in the universe. Gamma-rays are at the wrong end of the spectrum!
“We came up with a crazy idea to use WISE’s infrared observations, which are typically associated with lower-energy phenomena, to spot high-energy blazars, and it worked better than we hoped,” said Franceso Massaro of the Kavli Institute for Particle Astrophysics and Cosmology near Palo Alto, Calif., and principal investigator of the research.
So the idea wasn’t that crazy after all.
Blazars are basically active supermassive black holes lurking in the centers of massive galaxies. As matter — gas, dust, stars, aliens — gets eaten by the black hole’s feeding frenzy, the complex environment close to the black hole can create powerful collimated jets of superheated material blasting from the galactic core. These jets are accelerated to nearly the speed of light. Beams of highly concentrated gamma-rays are then generated as a consequence — so to see a blazar from Earth, one of the jets need to be pointed right at us.
“Blazars are extremely rare because it’s not too often that a supermassive black hole’s jet happens to point towards Earth,” said Massaro.
Now this is where WISE can help out. As the particles in the blazar jets are accelerated to relativistic speeds, they generate a signature infrared glow that WISE can see.
Hundreds of gamma-ray sources have been spotted by NASA’s Fermi space telescope, but there has been little evidence to confirm that all of the sources are in fact generated by blazars. Now that astronomers have turned to WISE for help, the infrared signature known to be associated with blazars can be sought out, confirming (or denying) which gamma-ray sources come from active galactic cores and others that may remain a mystery.
“This is a significant step toward unveiling the mystery of the many bright gamma-ray sources that are still of unknown origin,” said Raffaele D’Abrusco, a co-author of the papers from Harvard Smithsonian Center for Astrophysics in Cambridge, Mass. “WISE’s infrared vision is actually helping us understand what’s happening in the gamma-ray sky.”
Images: top: This artist’s concept shows a “feeding,” or active, supermassive black hole with a jet streaming outward at nearly the speed of light (NASA/JPL-Caltech); middle: NASA’s Wide-field Infrared Survey Explorer (WISE) shows a blazar — a voracious supermassive black hole inside a galaxy with a jet that happens to be pointed right toward Earth (NASA/JPL-Caltech/Kavli)