Project 1640 Sifts Through Starlight to Reveal New Worlds

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Hale telescope
The Project 1640 instrument mounted at the focus of the 200-inch Hale telescope. 
R. Oppenheimer/© AMNH

An advanced telescope imaging system that started taking data last month is the first of its kind capable of spotting planets orbiting suns outside of our solar system. The collaborative set of high-tech instrumentation and software, called Project 1640, is now operating on the Hale telescope at the Palomar Observatory in California, where it uses a new starlight-suppressing technique to see dim planets and other celestial objects in the star’s neighborhood. A large portion of the imaging system was developed and tested in the Museum’s optics laboratory by Rebecca Oppenheimer, an associate curator in the Department of Astrophysics and principal investigator for the project.

After more than six years of development by researchers and engineers at the Museum, the California Institute of Technology, and the Jet Propulsion Laboratory, Project 1640 presented its first images demonstrating the new technique today at the International Society for Optics and Photonics (SPIE) Astronomical Telescopes and Instrumentation meeting in Amsterdam. The project now begins a three-year survey, during which the researchers plan to image hundreds of young stars.

Although many planets are known to orbit other stars, it’s extremely difficult to see them directly in an image. This is largely because the light that stars emit is much brighter than the light given off by planets.

“We are blinded by this starlight,” Oppenheimer said. “Once we can actually see these exoplanets, we can determine the colors they emit, the chemical compositions of their atmospheres, and even the physical characteristics of their surfaces.”

Project 1640 is based on four major instruments that image infrared light generated by stars and the warm, young planets orbiting them. This is achieved by creating an “artificial eclipse” that blocks the extremely bright light emanating from the star. Even though the scientists are imaging what are considered relatively nearby stars—those no more than 200 light years away—an extraordinary level of precision is needed to produce accurate results.

After the starlight is filtered out of the image, about half of a percent of that light remains in the form of a bright speckled background superimposed on the solar systems of interest. Each of these speckles can be hundreds of times brighter than the planets and must be controlled with exquisite precision.

Two images of HD 157728, a nearby star 1.5 times larger than the Sun. The star is centered in both images, and its light has been mostly removed by the adaptive optics system and coronagraph. The remaining starlight leaves a speckled background against which fainter objects cannot be seen. On the left, the image was made without the ultra-precise starlight control that Project 1640 is capable of. On the right, the wavefront sensor was active, and a darker square hole formed in the residual starlight, allowing objects up to 10 million times fainter than the star to be seen. Images were taken on June 14, 2012, with Project 1640 on the Palomar Observatory’s 200-inch Hale telescope. Photo courtesy of Project 1640

Project 1640 has demonstrated a technique that can darken the speckles far beyond any previous capability, carving a dark square in the speckle background centered on the star. In June, the effect of this dark hole on an actual star was observed through a telescope for the first time.

The instruments are now in operation and producing some of the highest-contrast images ever made, revealing celestial objects 1 million to 10 million times fainter than the star at the center of the image.

For more information, read the Museum’s press release.