The most luminous objects in the cosmos are actually invisible to the naked eye.
They are called “blazars,” mysterious objects that glow not just with visible light—the kind our eyes can see—but with every kind of radiation, from radio waves to gamma rays.
If we could see the cosmos with gamma-ray eyes, blazars would dominate the night sky.
A team at Boston University is trying to understand how blazars work and where they get their tremendous energy. They think supermassive black holes containing the mass of hundreds of millions of suns power them.
But how do black holes—where gravity is so strong that nothing, not even light, can escape—power the brightest objects in the cosmos?
When the first blazar was discovered in 1962, astronomers were stumped: They did not know what it was and had never seen anything like it. But time and technology, like NASA’s Hubble Space Telescope, have yielded some clues. Today, astrophysicists have catalogued thousands of blazars.
First, astronomers tracked blazars to ancient galaxies located hundreds of millions, or even billions, of light years from Earth. Each of these galaxies, like our own Milky Way, is centered on a supermassive black hole that’s engulfed millions of suns’ worth of matter.
Somehow, researchers think, those behemoth black holes must be firing up the blazars.
Well-Fed Black Holes
But even though nearly every galaxy has a supermassive black hole, only a small fraction of galaxies—about one in ten—is an “active” galaxy, radiating a huge amount of energy. And fewer than one in a thousand active galaxies is a blazar. What makes them different?
