Night sky recorded in unprecedented sharpness

New adaptive optics make terrestrial telescopes look like Hubble

Star cluster in the Orion Nebula, taken with the Hubble telescope (background) and magnified images of the MagAO system © Laird Close and Ya-Lin Wu; NASA, CR O'Dell and SK Wong
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They even show the starry sky twice as sharply as the Hubble Space Telescope - even though the telescope is on Earth: With the aid of a new technology, an international team of astronomers has succeeded in capturing the highest-resolution images of the night sky. This was made possible with the help of a special vibrating mirror that compensates for atmospheric distortions. The resulting resolution is sufficient to see a tennis court on the moon from Earth.

The starry sky has always fascinated people. Since the 17th century, astronomers have been trying to sharpen their view of the sky with technical means. But if you look from the earth into the sky, there is a problem: The air movements of the atmosphere distort the view of the stars and blur the resulting image. With the naked eye, this effect can be recognized by the twinkling of the stars. Among other things, for example, the Hubble Space Telescope is stationed in Earth orbit - it flies above the disturbing atmosphere.

Recordings at the resolution limit of visible light

But there is another possibility: the so-called adaptive optics. At the same time, software compensates for the distortions of the atmosphere, or the mirror itself is movable and thus adapts to the turbulence of the air. A combination of both has been researched by researchers led by project manager Laird Close from the University of Arizona in Tucson in 20 years of work. The new system was now mounted on the 6.5 meter Magellan telescope of the Las Campanas Observatory in Chile. For the first time ever, a telescope with such a large primary mirror can take digital pictures at the resolution limit of visible light.

The Magellan telescope with the above-mounted, adaptive secondary mirror, below the primary mirror © Yuri Beletsky / Las Campanas Observatory

For the new "Magellan Adaptive Optics", the researchers installed a second, just two millimeters thin special mirror on the telescope. This floats - held by a magnetic field, about nine meters above the primary mirror. The special feature: This so-called adaptive secondary mirror can change its shape at 585 points on its surface. They vibrate about a thousand times a second to compensate for the trembling of the air in the field of view of the telescope.

A coin from 150 kilometers away

The test on the "First Light" of the Magellan telescope upgraded in this way was a complete success, as the researchers report. "It was exciting to see this new camera imaging the night sky more than ever before, " Close said. For the first time, you can take pictures of objects as small as 0.02 arc seconds - the size of a coin viewed from more than 150 kilometers away. The sharpness of the images even exceeds that of the Hubble Space Telescope by a factor of two - as this one does not have to worry about turbulence, but it only has a mirror about 3.50 meters high. display

Comparison without (left) and with adaptive optics - the resulting image is 17 times sharper. On the far right, a detail enlargement of the middle image. It shows that even the previously invisible double star system Theta Ori C with MagAO can now be seen separately. Laird Close / UA

Already the first shots of the new camera at the Magellan telescope proved the efficiency of the system: The astronomers targeted Theta 1 Ori C, a star system in the Orion Nebula. Although this binary star is so large and so bright that its point of light can be seen even in the sky with a simple pair of binoculars, it has not been possible to visually separate the two stars of this system.

"I've been observing Theta 1 Ori C with different telescopes for 20 years, but I've never directly seen that it's two stars, " says Close. "But as soon as we turned on the MagAO system, the diffused light point splitted beautifully into two separate stars."

(University of Arizona, 23.08.2013 - NPO)