Keck twins open new paths to universe
By Jan TenBruggencate
Advertiser Science Writer
Astronomers for the first time have been able to take the measurements of a black hole in a galaxy 40 million light years away using the combined power of the twin W.M. Keck telescopes atop Mauna Kea.
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"It's just fabulous. It's really an achievement ... Even with the biggest telescopes on Earth, all you see is a point of light. We actually took a measurement, for the first time ever," said Keck Observatory stellar astronomer David Le Mignant.
The twin Keck observatories, beyond Japan's Subaru Telescope, are proving their value atop Mauna Kea.
The observations were made May 19 and 20 by a team of scientists from NASA's Jet Propulsion Laboratory, the California Association for Research in Astronomy, and the CalTech Michelson Science Center. The findings will be published Oct. 20 in Astrophysical Journal Letters.
The two Keck telescopes, each with a mirror 33 feet across, were trained on a galaxy called NGC 4151. Each telescope used adaptive optics to reduce distortion from the Earth's atmosphere, and light from the two scopes was combined in an interferometer, simulating a much more powerful telescope with a mirror 279 feet across.
NGC 4151 is in a class called Seyfert Galaxies, which have huge, energetic black holes at their centers. While NGC 4151 is about the size of our own galaxy, its black hole is estimated to be 10 million times as massive as the sun, and 10 times the size of the black hole at the heart of the Milky Way.
A black hole's gravitational pull is so powerful that nothing, not even light, can escape. But at the fringes of a black hole is a doughnut-shaped ring of material spinning around, getting ready to be sucked in. The material in this accretion disk gets hotter before it enters the black hole, and as it gets hotter, it emits light that can be measured.
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When astronomers studied the data from the Keck interferometer, they found that infrared light came from a much more defined area than they expected. It appeared to be coming from the black hole's accretion disk and not just from the surrounding dust, said Rachel Akeson, an astronomer with the Michelson Science Center.
"What we were observing is material being sucked into the black hole," said Keck optical scientist Peter Wizinowich, interferometer team leader.
Akeson said interferometers on smaller telescopes have been able to look at things within our own solar system, but never this far away.
Wizinowich said there was some question whether the observation would be successful.
"We were unsure whether we would see anything. It's pushing the edge of the interferometer. It's a distant, faint object," he said.
The challenge for astronomy now will be to improve the telescopes.
"This is just the starting edge of what the instrument is ultimately capable of," he said.
The Keck interferometer is part of NASA's Origins Program, which seeks to discover the source of life on Earth and elsewhere.
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.
