A WISE Investment in Astronomy
By Joe Bauman
July 22, 2011
Last week, astronomers at the Leibniz Institute for Astrophysics, Potsdam, Germany, announced they had discovered two brown dwarf stars 15 light-years and 18 light-years from Earth, among the closest such objects known.
According to the institute, "Ralf-Dieter Scholz and his AIP colleagues used the recently-published data of the NASA satellite WISE (Wide-field Infrared Survey Explorer) for their discovery." The brown dwarfs, often called failed stars, were detected because they are almost invisible in normal light but shine brightly in the infrared, meaning they are giving off more heat than ordinary stars that are distant enough to be that dim. They also were moving rapidly.
The 16-inch diameter WISE space telescope, dedicated to infrared imaging, was designed and built by Utah State University's Space Dynamics Laboratory, North Ogden.
Launched into orbit on Dec. 14, 2009, WISE mapped the sky in infrared, basically heat readings that are blocked by the atmosphere. Images returned of everything from galaxies to asteroids, comets, stars and brown dwarfs are different from those made in light that we can see. The views detail new aspects of the targets.
The brown-dwarf discovery is among a great many surprises expected to be dug out of the millions of images that WISE took, 57 percent of which were released for public scrutiny in April.
"There are large communities of infrared astronomers around the world who are mining these databases," said John D. Elwell of the Space Dynamics Lab, who was WISE's lead engineer. "They're going to be mining this for the rest of my life, I'm sure."
Elwell, recently appointed program manager of a weather satellite project, spoke Tuesday during the monthly meeting of the Salt Lake Astronomical Society, held on the University of Utah campus.
WISE detected more than 30,000 new asteroids, Elwell said. They were "much brighter in the infrared than in the visible, 100 to 400 times brighter," he said.
Distant galaxies, brown dwarfs and galaxies that were ultra-bright in the infrared also were bagged by the nine-foot-tall satellite.
"We've categorized about a quarter of a billion unique sources so far," he said. A great deal of follow-up is planned with NASA's Spitzer infrared space telescope, the Hubble space telescope and ground-based scopes, he added.
The advantage of WISE over Spitzer is that the former was able to chart the entire sky in six months, while Spitzer -- with a far narrower field of view -- would take 38 years. After all, the W in WISE stands for Wide-field.
WISE cost about $320 million with $76 million spent at USU. Elwell said the lab did its job within budget and met its deadlines.
Frozen hydrogen coolant, needed to keep two of the four cameras cold enough to operate without interference from the telescope's own heat, chilled the equipment to -430 F. The coolant ran out last October, as expected. The remaining two cameras worked for another four months, until the telescope was put into hibernation in late February.
Each camera photographed the cosmos differently, as they were sensitive to four wavelengths of infrared light representing differing temperatures. Each of these wavelengths is invisible to the human eye. When images are combined using artificial colors for the separate wavelengths -- blue, cyan, green and red -- striking differences stand out, with particular colors indicating certain classes of objects.
Asteroids were found to have a startling variation in heat.
Some of the brown dwarfs are at room temperature, as these are gigantic balls of gas that did not ignite as stars.
"Ultraluminous galaxies don't sit in the color range that we expected," Elwell noted.
Each of the cameras cost about $2 million, he said.
Filling the coolant tank took at least nine weeks. "Not only are the safety issues [working with liquid, then frozen, hydrogen] pretty intricate, so are the issues of overfilling, underfilling." The final filling happened with the satellite perched atop its Delta II rocket at Vandenberg Air Force Base, CA.
The orbiting telescope's photos were radioed to Earth four times a day from hundreds of miles above ground. Millions were sent back to NASA, more than half of which have been released.
The rest of the views should be made public in March 2012. So far, said NASA's Fengchuan Liu, WISE project manager at the Jet Propulsion Laboratory, "the preliminary data contain millions of newfound objects."
WISE has discovered more than 20 comets. Of the asteroids and comets it found, 134 are near-earth objects that can come within 28 million miles of Earth's orbit; 21 are considered hazardous, although none of these is in the dinosaur-extinction class.
"It was a success!" Elwell said of the project.
Undoubtedly, more discoveries wait amid the images.
Scientists and backyard astronomers alike may study the data, available HERE. Maybe some amateur combing through the pictres will make the find of a lifetime.