A telescope calibrated by scientists from the National Institute of Standards and Technology (NIST), Harvard University and the University of Hawaii may help astrophysicists answer long-held questions about the universe’s expansion.
NIST scientists traveled to the summit of Haleakala volcano in Hawaii to tweak the operation of billions of light-collecting pixels in the Pan-STARRS telescope, which scans the sky for Type IA supernovae. These dying stars always shine with the same brilliance as other Type IA supernovae, making them useful methods to judge distance in the universe. Any visible shift in the supernova’s spectrum gives a calculation of how the universe has expanded or shrunk as the light traveled from the supernova to Earth.
“Because Type IA’s can be used as signposts, astrophysicists want to be sure that when they observe one of these faraway stellar cataclysms, they are getting a clear and accurate picture-particularly important given the current mystery over why the rate of expansion of the universe appears to be increasing,” NIST says. This required a telescope that will return reliable information about supernovae.
NIST's John Woodward says that NIST was more than ready to lend a helping hand. “We specialize in measurement, and they needed to calibrate the telescope in a way that has never been done before,” he explained.
Run-of-the-mill calibrations involve a telescope’s performance at many light wavelengths simultaneously, but Pan-STARRS had to be calibrated at several individual wavelengths between 400 and 1,000 nanometers. To accomplish this, Woodward and his colleagues used a special laser whose wavelength can be tuned to any value in that range, and spent three days testing the telescope’s huge 1.4 gigapixel camera–the largest in the world, Woodward says.
“Pan-STARRS will scan the same areas of the sky repeatedly over many months,” he says. “It was designed to look for near-Earth objects like asteroids, and it also pulls double duty as a supernova hunter. But for both jobs, observers need to be sure they can usefully compare what they see from one image to the next.”
Woodward says that because this is a pioneering telescope calibration, it is uncertain just how much effect the team’s work will have, and part of their future work will be deciding how much they have reduced the uncertainties in Pan-STARRS’s performance. They will use this information to calibrate a much larger telescope–the Large Synoptic Survey Telescope, planned for construction in Chile.