CfA researchers discover black holes aren’t so black

Common wisdom holds that we can never see a black hole because nothing can escape it – not even light. Fortunately, black holes aren’t completely black. As gas is pulled into a black hole by its strong gravitational force, the gas heats up and radiates. That radiation can be used to illuminate the black hole and paint its profile.

Within a few years, astronomers believe they will be able to peer close to the horizon of the black hole at the center of the Milky Way. Already, they have spotted light from “hot spots” just outside the black hole. While current technology is not quite ready for the final plunge, Harvard theorists Avery Broderick and Avi Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA), already have modeled what observers will see when they look into the maw of this monster.

“It will be really remarkable when observers can see all the way to the edge of the Milky Way’s central black hole – a hole 10 million miles in diameter that’s more than 25,000 light years away,” said Broderick.

All it will take is a cross-continental array of submillimeter telescopes to effectively create a single telescope as large as the Earth. This process, known as interferometry, has already been used to study longer-wavelength radio emissions from outer space. By studying shorter-wavelength submillimeter emissions, astronomers could get a high-resolution view of the region just outside the black hole.

“The Holy Grail of black hole astronomy is within our grasp,” said Broderick. “We could see the shadow that the black hole casts on surrounding material, and determine the size and spin of the black hole itself.”