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The Honolulu Advertiser
Posted on: Wednesday, December 20, 2006

Grant will deepen black hole research

By Kevin Dayton
Advertiser Big Island Bureau

Improvements to the Keck Observatory telescopes atop Mauna Kea will enable scientists to more closely monitor the wobble in stars caused by their planets' gravitational pull.


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HILO, Hawai'i The National Science Foundation has awarded $2 million to the W.M. Keck Observatory to enhance images collected by the powerful twin telescopes at Keck. The improvements will be used by astronomers to test a theory about the behavior of stars near black holes, and to obtain proof that black holes spin.

Closer to home, upgrading the interferometer system that combines light from Keck's twin telescopes on Mauna Kea also is expected to help astronomers calculate the masses of planets that orbit distant stars.

Astronomers already have found more than 200 planets outside of our solar system, and Keck has been used to confirm about two-thirds of those discoveries. The improvements at Keck will allow scientists to more precisely observe the wobble in stars caused by their planets' gravitational pull, making the calculations of the mass of the planets' possible.

The core of the project will be the "difficult and technically challenging" study of the black hole near the center of our Milky Way Galaxy, said project scientist James R. Graham, professor of astronomy at the University of California, Berkeley.

Black holes are bodies so massive they exert a gravitational pull so powerful that even light cannot escape.

Principal investigator Peter Wizinowich, a senior scientist at the Keck Observatory, said the improvements in the interferometer will make Keck "a unique instrument for measuring the position, velocity and acceleration of stars near the massive black hole at the center of our own galaxy, allowing us to look for the distortions in space predicted by (Albert Einstein's theory of) general relativity."

One major improvement to Keck that would be financed with the grant is a "phase referencing" system on the interferometer to allow longer exposures.

With phase referencing, the interferometer will be able to track an object 100 to 500 times longer than before, and the longer exposure time will allow the instrument to study objects that are too faint to be seen now.

The second part of the three-year project will advance the interferometer's ability to accurately measure positions of celestial objects.

Overall, the improvements will allow the linked Keck telescopes to observe objects 100 times fainter than with the existing interferometer, and measure the apparent positions of celestial objects with 10 times more accuracy than a Keck telescope working alone.

With those new capabilities, astronomers plan to map out "incredibly detailed and precise" data on stars orbiting the black hole over time, said Taft Armandroff, director of Keck Observatory.

"Many phenomena in astronomy you have to wait awhile to see them happen, but because this black hole is so massive, the speeds that these stars are moving around the galactic center are large, so you can see the movements," he said.

Then astronomers will compare those observations with computer models developed to predict how the stars should move based on scientists' understanding of general relativity, their assumptions about the mass of the black hole, and whether the black hole is rotating, Armandroff said.

If astronomers' assumptions are correct, the observations should match the model. If not, the challenge will be to find the flaw in the model.

The W.M. Keck Observatory is operated by the California Association for Research in Astronomy, which is overseen by directors from the California Institute of Technology and the University of California.

Reach Kevin Dayton at kdayton@honoluluadvertiser.com.