Keck Observatory Awarded $2M to Improve Interferometer

The National Science Foundation has awarded the W. M. Keck Observatory $2 million to improve the sensitivity and resolution of the Keck Interferometer. The improvements will enable the instrument to detect Jupiter-sized planets around other stars and test predictions of Einstein's general theory of relativity in the chaotic core of the Milky Way galaxy.

The three-year grant is from National Science Foundation's (NSF) Major Research Instrumentation Program. Typically, less than one-half of one percent of all submitted proposals receive the maximum award of $2 million, and only a few go to astronomical observatories.

The Keck Interferometer combines the light from the two 10-m-diameter Keck telescopes. A $2 million grant from the National Science Foundation will allow the linked telescopes to observe objects 100 times fainter than the existing interferometer and measure the positions of celestial objects with 10 times more accuracy than each telescope working alone. (Photo: W. M. Keck Observatory)

The grant funds two major telescope improvements: installation of a phase referencing system on the interferometer that will allow longer exposures, and thus detection of fainter objects; and upgrading of the interferometer to be able to perform accurate measurements of a star's position.

"The interferometer improvements will make Keck Observatory 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 general relativity," said principal investigator Peter Wizinowich, a senior scientist at the observatory.

The money will be used to boost the sensitivity of the 85-m baseline Keck Interferometer, which combines the light from the two 10-m-diameter Keck telescopes. Combined with laser guide star adaptive optics on both telescopes, the improvements will allow the linked telescopes to observe objects 100 times fainter than the existing interferometer and measure the apparent positions of celestial objects with 10 times more accuracy than a single telescope working alone.

Observations near the black hole at the center of the galaxy "are at the core of the project and will be difficult and technically challenging," said project scientist James R. Graham, professor of astronomy at the University of California, Berkeley.

Even before this goal is achieved, the upgrades will allow the interferometer to help determine the mass of extrasolar planets by measuring the periodic change in the position of parent stars caused by the tug of unseen planets. Currently, more than 200 extrasolar planets have been detected due to the radial velocity or "wobble effect" they induce on their parent star. About two-thirds of all known extrasolar planets have been confirmed at the Keck Observatory. The interferometer will add precise orbital measurements to the existing catalog of radial velocity data to help precisely determine the mass of extrasolar planets the size of Jupiter and larger.

Because related NASA projects have been shelved, the Keck Interferometer will be the only instrument in the world capable of measuring accurate masses for planets around distant stars.

With the added improvements, the Keck Interferometer will resolve objects on the sky to an accuracy of 30 microarcseconds, compared to about 300-microarcsecond resolution of each telescope alone. Such fine measurements will allow scientists to measure the velocities of stars orbiting the black hole at the center of the galaxy.

The hope, Graham said, is to detect in the stellar orbits the effect of the dragging of "inertial reference frames" predicted to occur near a rapidly rotating black hole. This effect is predicted by Newton's laws of motion for mass located very near a spinning black hole. Scientists using the Keck Interferometer may be able to see this effect, which would be major breakthrough in tests of general relativity and other theories of gravity. The observations could also prove that black holes spin, thus constraining theories of their formation.

"This is a major opportunity to show astronomers what interferometry can do for them," Wizinowich said. "Every time astronomers look in more detail at the sky, they learn something new."

Scientific collaborators on the NSF proposal include: Julien Woillez, Keck Observatory; Andrea Ghez, University of California, Los Angeles; Rachel Akeson and Lynne Hillenbrand, California Institute of Technology; Josh Eisner and Eliot Quataert, University of California, Berkeley; Nevin Weinberg, University of California, Santa Barbara; and John Monnier, University of Michigan.

For more information, visit: www.keckobservatory.org