A proposal for a new space-based observatory led by Johns Hopkins researchers has taken a step closer to reality. NASA officials announced in September that the Primordial Explorer project, known as PRIME, was among seven finalists for NASA's Small Explorer program.
Beginning in October 2001, NASA will give Hopkins researchers funding to conduct six months of "Phase A" concept studies of technical aspects of PRIME. Final selection of two projects for full funding will be based on data from the concept studies.
Wei Zheng, PRIME principal investigator and a research scientist in the Department of Physics and Astronomy, and colleague Zlatan Tsvetanov, an associate research professor, said that PRIME will be designed to study the distant early universe by detecting and analyzing weak infrared radiation. Light from objects beyond the galaxy gets shifted into the red as it travels toward Earth; the farther away the object, the greater this shift into the red.
Earth's day and night skies are lit with a bright infrared haze that makes it very difficult to see much of the infrared radiation coming from distant galaxies, just as sunlight makes it difficult to see most stars during the day. If approved, PRIME will observe the universe from a point in orbit beyond much of the haze, enabling a unique slate of its own scientific missions and allowing it to provide important assistance to a much larger initiative, NASA's Next Generation Space Telescope.
NGST's primary objective is to study the early universe, so it also will observe mainly in the infrared. From a perch beyond the orbit of the moon, NGST will be able to detect radiation from the distant universe with unprecedented sensitivity.
Astronomers can learn the most about the distant universe from rare and unusual objects. NGST can give them a highly detailed look at those objects, but they've got to find the rare objects first, a job more suited to an instrument capable of surveying wider swaths of space in less detail. PRIME would be ideal for this task.
PRIME's own scientific missions center on its potentially keen ability to find rare objects such as high redshift quasars, type 1a supernovae, brown dwarfs and massive, Jupiter-like planets.
High redshift quasars, which emit incredible amounts of energy, are thought to be distant galaxies with supermassive black holes in their centers. The higher a quasar's redshift, the faster it is traveling away from Earth and the more distant it is.
The current record for a quasar's redshift is 5.8. PRIME could detect quasars with redshifts as high as 25, if they exist. This prospect has astrophysicists like Zheng and Tsvetanov excited.
Higher redshifts, Zheng notes, aren't just connected to speed and distance. They're also connected to cosmic time. Higher redshifts mean observers are looking further back into history at a younger, unknown universe.
"Imagine if you were an alien observing life on the Earth, and you were only able to observe humans from the age of 10 and up," Zheng says. "The changes in those decades are relatively minor compared to those that occur between birth and the age of 10, and PRIME could put us on the brink of filling in similarly dramatic gaps in the origins and development of quasars."
PRIME also would allow astronomers to find hundreds or perhaps thousands of rare exploding stars known as type 1a supernovae. Astronomers know how bright these stars should be, and can factor that into a supernova's observed brightness to get an unusually accurate idea of how far away the supernova is. This in turn can help answer fundamental questions about the rate at which the universe is expanding.
On a cosmologically "local" level, PRIME would allow astronomers to search for brown dwarfs, small, cool, gaseous bodies that are an important step in the transition between gas giant planets like Jupiter or Saturn and stars.
PRIME also would allow astronomers to see any Jupiter-sized or bigger "free-floating" planets close to Earth, an important first. Scientists have already detected dozens of planets orbiting other stars, but they currently can detect them only indirectly, by observing the slight wobbles a planet's gravity creates in its home star.
"For PRIME to image it, a planet would have to be within a radius of a few light-years of Earth and relatively young, perhaps a billion years old or so," Tsvetanov says. "If such a planet exists, PRIME should be able to see it."
Additional targets for PRIME observation would include distant objects such as galactic clusters and closer regions like the Kuiper Belt, an area on the outskirts of the solar system where most comets originate.
"The prospects for PRIME are very exciting," says Ethan Vishniac, director of Hopkins' Center for Astrophysical Studies, which is supervising the PRIME proposal. "It would increase our knowledge of a wide range of objects both near and far, supplement current work under way to map a large portion of the sky and provide a vast array of useful targets for the NGST."
Other Hopkins researchers on the PRIME development team are deputy principal investigator Holland Ford, Arthur Davidsen and Alex Szalay, all professors; and Jeff Kruk, a research scientist.
Other research institutions involved are the Space Telescope Science Institute, Goddard Space Flight Center, the University of Arizona, the Max-Planck-Institut fuer Astronomie in Heidelberg, Germany, and the Swales Aerospace Corp.