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Largest class of terrestrial telescopes produce important results

From OE Reports Number 194 - February 2000
31 February 2000, SPIE Newsroom. DOI: 10.1117/2.6200002.0005

Since the launch of the Hubble Space Telescope, public attention has been focused upward-not only on the stars, but on the telescope itself. Several miles below, however, the world's largest telescopes are quietly looking across time to the beginning of our universe, making discoveries that have mostly gone unappreciated by all but astronomers.

Figure 1. The Large Binocular Telescope under construction on Mt. Graham in Arizona will have two 8.4-m telescopes on a single mount with the center of each telescope separated by approximately 13 m.

Now, as international groups prepare to build and launch the Next-Generation Space Telescope, public imagination will likely be captured once again by "eyes in the sky." Meanwhile, earthbound explorers of space persevere in their endeavor to discover the origins of life.

Looking behind -- far, far behind

"I think that one of the most important discoveries has already been made at Keck, and that's the discovery of these high-red-shift galaxies," said Robert Kennicutt of the Steward Observatory in Arizona. "The Hubble has the ability to discover these very faint objects that are essentially at 10 percent the present age of the universe, but you need more light-accumulating power to get the full spectrum and measure their properties...The work done at Keck is a perfect example of the kinds of discoveries that will remain the areas of greatest growth for the next 10 to 15 years."

Red-shift refers to the peak emission strength of a celestial object. The older the object, the farther the peak travels from visible to near-IR to mid-IR at 20 µm and beyond. "At Keck, we're seeing galaxies that were progenitors of the Milky Way," said Michael Rich of UCLA. "And we're seeing them at about the same time the first quasars turned on." Time and space truly converge in the discipline of astronomy where light arriving at the Earth from distant galaxies is billions of years old, bringing images of how these objects looked shortly after the formation of the universe.

Figure 2. Discovering distant galaxies that were created around the same time as the creation of the universe will continue to be one of the most important areas of research made possible by the largest class of optical telescopes. This famous southern planetary nebula, the Butterfly (NGC 6302), was obtained on 22 May 1998, with 10-minute exposures and an image quality better than 0.6 arcseconds. (Image courtesy of the ESO).

Many other discoveries await the completion of several 8- to 10-m-class telescopes. Currently, the Keck Observatory is the first fully functional telescope of this size and stature. The European Space Organization has completed work on two of the four 8.5-m telescopes that comprise the Very Large Telescope in Chili, and work is also underway on the Subaru 8-m telescope on Mauna Kea (Hawaii) and the Large Binocular Telescope (LBT) planned for Arizona's Mt. Graham. According to Rich, these telescopes, in conjunction with advanced adaptive optics, interferometers, and spectrometers will help map planets outside our solar system as well as the surface of stars. They will allow astronomers to delve deeper into the mysteries of quasars, helium ionization and its link to the creation of our universe, and the first elements.

Technical hurdles remain

Because of the Earth's atmosphere, terrestrial telescopes may never have the detection ability of the 8-m Next-Generation Space Telescope. However, several instruments could help close the performance gap between space telescopes and Keck, VLT, LBT, and Subaru.

"Interferometry is going to be a major push for LBT, especially because it has two telescopes on the same mount," Rich said. "With an interferometer you can get 10 times (better measurements than using other terrestrial means) and rule out non-black-hole alternatives with much greater certainty."

Several systems of this kind are under development and test. Kennicutt, who sat on a review committee for interferometric devices at LBT, said, "They work on paper, but are not being implemented. Indications are that the technology is in place, but it's a system [integration] problem."

Adaptive optics, an area of active development over the past decade, is a crucial element in the inteferometry system. "This will essentially allow 8- to 10-m telescopes to take spectrums that have the resolution of spaceborne telescopes, but from the ground," Rich said. "But the catch is that adaptive optics only work really well on the long side of 2 µm and only sort-of well around 1 µm unless conditions are superb."

Imaging spectrographs in the IR are other instruments that will gain strength with improvements to adaptive optics. "Spectrographs will allow you to look at high-red-shift galaxies," Rich said, "and maybe-using adaptive optics and some very clever methods-get a clear image of a remote planet orbiting around another star."

R. Winn Hardin

R. Winn Hardin is a science and technology writer based in Jacksonville, FL.