UW prof builds infrared camera to explore universe

2012-05-28T22:42:00Z UW prof builds infrared camera to explore universeThe Associated Press The Associated Press
May 28, 2012 10:42 pm  • 

LARAMIE, Wyo. (AP) — University of Wyoming associate professor Mike Pierce is interested in the history of the universe, and an infrared camera he spent seven years building will help him study its oldest and most distant formations.

Pierce, who works in the Department of Physics and Astronomy, plans to use his Near-Infrared Imaging Spectrograph to view images in infrared wavelengths captured by a telescope.

As the universe expands and distant objects move apart, light they emit changes from optical into infrared wavelengths by the time it reaches earth. Capturing light from those distant objects requires special instruments. Infrared light is invisible to the eye because its wavelengths are outside the range of visible light on the electromagnetic spectrum.

"Light, as it traverses space, gets stretched as the space between whatever emitted the light and us is changing during the travel time for light," Pierce said. "That effectively stretches the wavelength."

The farther away an object is, the more time it takes for its light to reach earth. Light from the sun takes about eight minutes to reach earth. Light from the nearest star takes about four light years to reach the earth — a light year is about 6 trillion miles — meaning that we see that star as it appeared four years ago.

Looking at faraway objects, then, allows scientists to study the characteristics of a younger universe. Some of the most distant stars known to man were formed during the first 10 percent of the life of the universe.

"By looking at ever-greater-distant objects, we're effectively looking back in time. That allows us to study the evolution of the universe — how it's changed over time — by looking at how it changes with distance away from us," Pierce says.

Pierce, who came to UW in 2001 from the University of Indiana, received funding from the National Science Foundation, the state of Wyoming and NASA's Goddard Space Flight Center. Most of the construction work was done at UW except for the optics and the detector, which Pierce described as "kind of like the ones in your digital camera, except they cost half a million dollars."

Working with infrared light is not an easy task. Everything, including the camera itself, emits infrared radiation, so the equipment must be shielded from outside heat in order to isolate the light captured by the telescope.

"Otherwise, the thermal emission from the instrument itself would swamp the detector and dominate the signal that you would get from the telescope and outer space," Pierce said.

The camera, which weighs about a thousand pounds, sits inside a large cylinder that is sealed and insulated. To prepare the camera for operation, Pierce lowers the pressure inside to about a millionth of the atmospheric pressure outside, a process that takes a week. Otherwise, the equipment inside would frost up when cooled.

"If you allow moisture-laden air to contact the cold surfaces, it would instantly frost over," he said.

Once the air is removed, Pierce uses liquid nitrogen to lower the temperature inside to 300 degrees below zero, effectively shielding the camera from all infrared radiation except what comes in through the telescope. That process takes another week.

At the front, a window lets light in from a telescope. A series of lenses focus the images before the light travels through a filter wheel for specific ranges of infrared light, and then through another series of lenses. Finally, it reaches the detector at the back.

The 15 lenses are made of extremely fragile crystalline material that can, unlike glass, transmit infrared light and are held in place with special mounts that can adjust to the shrinking that occurs when the equipment is cooled.

"The lenses would just shatter if you tried to hold them in anything mechanical. They would just explode," Pierce said.

Pierce recently tested the camera at Apache Point Observatory in Sunspot, N.M., where it will be housed later this year. Its wide field of view allowed scientists to capture images about half the size of the full moon.

"That was one of the things that was a big deal about the camera, it's going to image an enormous area on the sky," Pierce said.

He estimated there are fewer than 10 similar instruments in the world, and nothing on that scale has ever been built at UW.

NASA's Goddard Space Flight Center provided funding to Pierce because his instrument will be useful in research conducted there, astrophysicist Neil Gehrels said.

Gehrels studies gamma ray bursts, which are big explosions that occur in distant galaxies. A satellite detects the explosions, which occur about twice a week, and transmits the location to the ground.

"Then we want to observe them quickly with other telescopes in space and on the ground," Gehrels said.

These bursts, the cause of which is still unknown, glow with infrared radiation.

"For the first day or so when you can observe them with telescopes, they're by far the brightest distant sources in the sky. You can use them to study the galaxy that they're in and learn about when stars first formed in the universe. You can use them to study the very early universe," he said.

Pierce hopes to soon upgrade the camera with a programmable microshutter array, that disperses light from multiple objects into their spectra or their component colors and wavelengths.

"If that comes to pass over the next year or two, then this camera that I've built will be the only camera in the world that has that technology," he said.

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