Isle scopes help to find evidence of a black hole

Astronomers using a network of radio telescopes, including two on Mauna Kea, have for the first time detected magnetic fields very near the black hole at the center of the Milky Way galaxy.

“These magnetic fields have been predicted to exist, but no one has seen them before,” Shep Doeleman, lead scientist on the study and assistant director of MIT’s Haystack Observatory, said in a statement Thursday. “Our data puts decades of theoretical work on solid observational ground.”

The Harvard-Smithsonian Center for Astrophysics announced the discovery, which is detailed in a paper to be published today in the journal Science.

The magnetic fields are just outside the edge or “event horizon” of the hole, the point at which swirling material vanishes.

The fields were detected by what is known as the Event Horizon Telescope, a network of radio telescopes rigged to function as one. They include the Submillimeter Array and the James Clerk Maxwell Telescope, both on Mauna Kea, the Submillimeter Telescope on Mount Graham in Arizona, and the Combined Array for Research in Millimeter-wave Astronomy near Bishop, Calif.

Together they formed essentially an Earth-size observatory which achieved the resolution necessary to see something so distant and compact. The team found that polarized light emitted by electrons spiraling around magnetic field lines directly traced the structure of the field.

In some regions the field lines are disorderly, “with jumbled loops and whorls resembling intertwined spaghetti,” the researchers said. Other regions showed a much more organized pattern.

They also found that the magnetic fields fluctuated on short time scales, changing shape every 15 minutes or so.

“Once again, the galactic center is proving to be a more dynamic place than we might have guessed,” said lead author Michael Johnson of the Harvard- Smithsonian Center. “Those magnetic fields are dancing all over the place.”

The research team said the Event Horizon Telescope will eventually be able to resolve features as small as 15 micro-arcseconds, the angular equivalent of seeing a golf ball on the moon.

A micro-arcsecond is a millionth of an arcsecond, which is one-3,600th of a degree.

The Milky Way’s central black hole weighs about 4 million times as much as the sun, yet its event horizon spans only 8 million miles — smaller than the orbit of Mercury. And because it’s 25,000 light-years away, its width from Earth’s perspective is an extremely small 10 micro-arcseconds.

Fortunately, the intense gravity of the black hole warps light and magnifies the event horizon so that it appears larger — about 50 micro-arcseconds, a region that the network can easily resolve.

As the network adds more radio dishes around the world, it will achieve greater resolution with the goal of directly observing a black hole’s event horizon for the first time, the astronomers said.