Keck Interferometer Team to Make Stars 'Disappear'
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What's left when you remove a star?
This demo illustrates how the bright light of a star obscures the faint surrounding material. NOTICE To view this demo, go to: http://planetquest.jpl.nasa.gov/ to the PlanetQuest page where this article originated. Once there, click on the art in the upper corner, then use the slider provided to "dim" the light and reveal a dust disk.
Interferometry: A new window on the Universe
With an instrument recently installed as part of the Keck Interferometer, they can make stars disappear almost completely from a telescope's view and reveal the close-in regions where planets may have formed. This fall, astronomers will continue integration and test of the instrument, called the "Nuller," which will contribute to NASA's search for planets around other stars.
"We have successfully combined infrared light from both 10-meter (33-foot) Keck telescopes using the new Nuller instrument," said Dr. Jim Fanson, Keck Interferometer project manager at JPL. "This permits a so-called 'visibility' measurement, where we can measure the size of objects with exquisite precision.
"Later this year, when we complete our functional tests of the Nuller, we'll be ready to attempt our first null measurement," Fanson said.
The Keck Interferometer is a NASA project that combines light from the world's largest optical telescopes to create a new type of telescope with unprecedented power. An interferometer is a device that gathers light waves from multiple telescopes, and then combines the waves in such a way that they interact, or "interfere" with each other. Depending on how the light waves are combined, they can combine constructively, creating higher intensity, or they can combine destructively, creating lower intensity The resulting light pattern, called an "interference fringe," can be decoded by astronomers to make high precision measurements, such as a star's diameter or the size of an accretion disk around a black hole.
Keck Interferometer team members transport part of the starlight nuller instrument in preparation for its installation inside the observatory.
The Nulling instrument is designed to combine the starlight waves destructively, so they cancel each other out. With the starlight glare suppressed, the faint light from dust orbiting around the star can be detected.
"You're getting rid of this great big searchlight that the star is, and you're seeing the faint stuff orbiting nearby that you normally can't see because of the glare," said Dr. Andrew Booth of JPL, software engineering lead for the Keck Interferometer.
The "faint stuff" that astronomers hope to glimpse with the Keck Interferometer Nuller is the exozodiacal dust (dust in the plane of other solar systems) that may surround many stars. It is the leftover material from which planets are believed to have formed. Large amounts of exozodiacal dust could obscure the signature of a planet. "This dust, if it's thick enough, could defeat our attempts to image planets around other stars from space telescopes now in the planning stages," Fanson said. "We need to find out how bright this dust is."
Nulling interferometry is considered an essential technology in NASA's quest for new planets. Although more than 100 planets have been detected around other stars in recent years, so far, none have been observed directly. This is because the relatively faint light of the planets is swamped in the brilliant glare of the stars they orbit. Future planet-finding missions, such a Terrestrial Planet Finder, will use nulling interferometry to directly observe and characterize planets around nearby stars.
Before shipment, the Keck Interferometer Nuller was tested extensively in a laboratory at JPL using a configuration similar to how it will be used on the sky. In these tests it was able to cancel 99.9 percent of the light from its test star, according to Dr. Mark Colavita, the project's instrument manager.
After years of development, seeing the instrument work for the first time produced feelings of both "relief and excitement," recalled Project Scientist Dr. Gene Serabyn, "It's a very challenging problem to make light of all wavelengths subtract away, so it took a while to find the proper technique. We had to come up with some newer and better ideas along the way to simplify the process," Serabyn said.
The development of the Keck Interferometer is managed by JPL for NASA's Science Mission Directorate, Washington. It is part of NASA's Origins program, a series of missions and studies designed to answer the questions: Where did we come from? Are we alone? The W.M. Keck Observatory is funded by Caltech, the University of California, and NASA, and is managed by the California Association for Research in Astronomy, Kamuela, Hawaii.
