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NASA has announced the development of a space-based observatory to give astronomers a new way to view X-rays from exotic objects such as black holes, neutron stars, and supernovae. Called the Gravity and Extreme Magnetism Small Explorer (GEMS), the mission is part of NASA’s Small Explorer (SMEX) series of cost-efficient and highly productive space-science satellites, and will be the first satellite to measure the polarization of X-rays sources beyond the solar system.
Polarization is the direction of the vibrating electric field in an electromagnetic wave. An everyday example of polarization is the attenuating effect of some types of sunglasses, which pass light that vibrates in one direction while blocking the rest. Astronomers frequently measure the polarization of radio waves and visible light to get insight into the physics of stars, nebulae, and the interstellar medium, but few measurements have every been made of polarized X-rays from cosmic sources.
“To date, astronomers have measured X-ray polarization from only a single object outside the solar system — the famous Crab Nebula, the luminous cloud that marks the site of an exploded star,” said Jean Swank, a Goddard astrophysicist and the GEMS principal investigator. “We expect that GEMS will detect dozens of sources and really open up this new frontier.”
Black holes will be high on the list of objects for GEMS to observe. The extreme gravitational field near a spinning black hole not only bends the paths of X-rays, it also alters the directions of their electric fields. Polarization measurements can reveal the presence of a black hole and provide astronomers with information on its spin. Fast-moving electrons emit polarized X-rays as they spiral through intense magnetic fields, providing GEMS with the means to explore another aspect of extreme environments.
“Thanks to these effects, GEMS can probe spatial scales far smaller than any telescope can possibly image,” Swank said. Polarized X-rays carry information about the structure of cosmic sources that isn’t available in any other way.
“GEMS will be about 100 times more sensitive to polarization than any previous X-ray observatory, so we’re anticipating many new discoveries,” said Sandra Cauffman, GEMS project manager and the Assistant Director for Flight Projects at Goddard.
Some of the fundamental questions scientists hope GEMS will answer include: Where is the energy released near black holes? Where do the X-ray emissions from pulsars and neutron stars originate? What is the structure of the magnetic fields in supernova remnants?
GEMS will have innovative detectors that efficiently measure X-ray polarization. Using three telescopes, GEMS will detect X-rays with energies between 2,000 and 10,000 electron volts. (For comparison, visible light has energies between 2 and 3 electron volts.) The telescope optics will be based on thin-foil X-ray mirrors developed at Goddard and already proven in the joint Japan/U.S. Suzaku orbital observatory.
GEMS will launch no earlier than 2014 on a mission lasting up to two years. GEMS is expected to cost $105 million, excluding launch vehicle.
Orbital Sciences Corporation in Dulles, Va., will provide the spacecraft bus and mission operations. ATK Space in Goleta, Calif., will build a 4-meter deployable boom that will place the X-ray mirrors at the proper distance from the detectors once GEMS reaches orbit. NASA’s Ames Research Center in Moffett Field, Calif., will partner in the science, provide science data processing software and assist in tracking the spacecraft’s development.
Source: NASA Goddard