Thursday, December 3, 2015

Telescope Finds Clue to Black Hole Growth

In this artist's conception, the black hole at the center of our galaxy is surrounded by a hot disk of accreting material. Blue lines trace magnetic fields. The Event Horizon Telescope has measured those magnetic fields for the first time with a resolution six times the size of the event horizon (6 Schwarzschild radii). It found the fields in the disk to be disorderly, with jumbled loops and whorls resembling intertwined spaghetti. In contrast, other regions showed a much more organized pattern, possibly in the region where jets (shown by the narrow yellow streamer) would be generated. Credit: M. Weiss/CfA

A new discovery, published today in the journal Science, has greatly deepened our understanding black holes, which are believed to be the gravitational engines at the centers of most galaxies, including our own. Using an array of telescopes that spans the globe, astronomers detected evidence of magnetic fields near Sagittarius A*, the 4.5-million-solar-mass black hole at the center of the Milky Way. "Understanding these magnetic fields is critical. Nobody has been able to resolve magnetic fields near the event horizon until now," says lead author Michael Johnson of the Harvard-Smithsonian Center for Astrophysics (CfA).

Decades of theoretical work, including enormous computer simulations, have painted a picture of how strong horizon-scale magnetic fields near the black hole contribute to its growth. Now that this international collaboration has discovered high levels of polarization in the radio emissions from Sagittarius A*, physicists have proof that these magnetic fields indeed exist.

Were these magnetic fields not there, “a lot theoretical astrophysics would have to go back to the drawing board,” says Avery Broderick, an Associate Faculty member at Perimeter Institute for Theoretical Physics, jointly appointed at the University of Waterloo.

"These magnetic fields have been predicted to exist, but no one has seen them before. Our data puts decades of theoretical work on solid observational ground," adds principal investigator Shep Doeleman (CfA/MIT), who is assistant director of MIT's Haystack Observatory.

A delightful comic illustrates how the Event Horizon Telescope can measure magnetic fields at our galaxy's core. Credit: Event Horizon Telescope
A delightful comic illustrates how the Event Horizon Telescope can measure magnetic fields at our galaxy's core. Credit: Event Horizon Telescope

Researchers achieved this new finding using the Event Horizon Telescope – an interconnected array of millimeter-wavelength telescopes located around the world. Together, they form an Earth-sized telescope capable of extremely high resolution, which, in the near future, will enable astronomers to image the event horizon of a black hole for the first time in human history.

“There are now enough telescopes in the array, in principle, to make images in the next couple of years,” Broderick added. “This might be the point, like the turn of the last century, when all of a sudden the puzzle pieces click into place.”

Those images will enable astrophysicists to transform our understanding of how black holes grow, how they interact with their surroundings, and even the nature of gravity.

“We are on the cusp of a true first in astronomical exploration,” says Avery Broderick. “We fully expect to have imaged a black hole’s event horizon in a matter of years. This would be an incredible accomplishment, not just for science, but humankind.”