Twins Combine Planetary Light
Astronomers have observed a young star ringed by a swirling disc that may spin off planets, marking the first published science observation using two linked 10-meter (33-foot) telescopes in Hawaii. Proving that two telescopes are better than one, NASA astronomers have started a new technique to search for planets around nearby stars and help design future space-based missions that can search for habitable, Earthlike planets.
|The combining of the light from the twin giants, and in the future, light from 2 smaller outrigger telescopes, will produce images capable of resolving Jupiter-size planets orbiting nearby stars.
The linked telescopes at the W.M. Keck Observatory on Mauna Kea, known as the Keck Interferometer , comprise the world’s largest optical telescope system. The observation was made of DG Tau, a young star that has not yet begun to burn hydrogen in its core. Such stars are called T-Tauri objects. Observations of DG Tau were made on October 23, 2002, and February 13, 2003, and the findings will appear in an upcoming issue of the Astrophysical Journal Letters .
"We’re trying to measure the size of the hot material in the dust disc around DG Tau, where planets may form," said Dr. Rachel Akeson, leader of the study team and an astronomer at the Michelson Science Center at the California Institute of Technology in Pasadena. "Studies like this teach us more about how stars form, either alone or in pairs, and how planets eventually form in discs around stars."
The Keck Interferometer observations revealed a gap of nearly 29 million kilometers (18 million miles) between DG Tau and its orbiting dust disc. Akeson notes that of the extra-solar planets — planets orbiting other stars — discovered so far, roughly one in four lies within 16 million kilometers (10 million miles) of the parent star. Since planets are believed to form within a dust disc, either DG Tau’s disc has a larger-than-usual gap, or the close-in planets form farther from the star and migrate inward.
"T-Tauri objects had been observed with other instruments, but only the brightest ones were detectable until now," Akeson said. "With the larger telescopes and greater sensitivity of the Keck Interferometer, we can look at fainter T-Tauri objects, like this one."
The Keck Interferometer gathers light waves with two telescopes and then combines the waves so they interact, or "interfere" with each other. It’s like throwing a rock into a lake and watching the ripples, or waves, and then throwing in a second rock. The second set of waves either bumps against the first set and changes its pattern, or both sets join together to form larger, more powerful waves. With interferometry, the idea is to combine light waves from multiple telescopes to simulate a much larger, more powerful telescope.
|Video: Click the image to view an animation depicting the concept of linking the two Keck telescopes on top of Mauna Kea, Hawaii.
In its ability to resolve fine details, the Keck Interferometer is equivalent to an 85-meter (279-foot) telescope. "The system transports the light gathered by the two telescopes to an optical laboratory located in the central building," said Dr. Mark Colavita of NASA’s Jet Propulsion Laboratory , Pasadena, interferometer system architect and lead author of the paper. "In the lab, a beam combiner and infrared camera combine and process the collected light to make the science measurement."
|Animation: Click on the image above for a description of Interferometry.
To make these measurements, the interferometer’s optical system adjusts the light paths to a fraction of a wavelength of light, and adaptive optics on the telescopes remove the distortion caused by Earth’s atmosphere.
"This research represents the first scientific application of an interferometer with telescopes that use adaptive optics," said Dr. Peter Wizinowich, interferometer team lead for the W.M. Keck Observatory and co-author of the paper.
"This is a major step in the creation of a whole new class of astronomical telescopes that will have an enormous impact on future knowledge," said Dr. Paul Swanson, the Keck Interferometer Project Manager at NASA’s Jet Propulsion Laboratory (JPL), Pasadena, CA. "Historically, breakthrough technologies like the Hale 200-inch and the Hubble Space telescopes have made discoveries way beyond the purpose for which they were originally built."
Since 1995, astronomers have detected more than 100 extra-solar planets, many considered too large and close to their hot, parent stars to sustain life. By measuring the amount of dust around other stars, where planets may form, the Keck Interferometer will pave the way for NASA’s Terrestrial Planet Finder mission. Terrestrial Planet Finder will look for smaller, Earth-like planets that may harbor life. The Keck Interferometer and Terrestrial Planet Finder are part of NASA’s Origins Program , which seeks to answer the questions: Where did we come from? Are we alone?
The Keck Observatory saw its first light in 1993. "Great telescopes like the Kecks allow us to explore the River of Time back toward its source", said astronomer Sandra Faber. "The Kecks will allow us, like no other telescope in history, to view the evolving Universe that gave us birth."
The development of the Keck Interferometer is managed by JPL for NASA’s Office of Space Science, Washington. JPL is a division of the California Institute of Technology in Pasadena. 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, HI.