A Goddard-led team now has a shot at building the world’s first telescope dedicated to measuring the polarization of high-energy X-ray light.
NASA recently selected Goddard’s Gravity and Extreme Magnetism SMEX (GEMS) team to receive $750,000 to carry out a detailed mission concept study, which is due this fall. Of the six missions selected for Phase-A studies, the Agency will select two next year for full development under the Small Explorer (SMEX) program. One of the two could launch as early as 2012.
Although team members will not speculate on their chances of winning, they nonetheless are optimistic. “I think our mission will fly eventually because it explores a new frontier in X-ray astronomy,” said Jean Swank, who is leading the mission, along with Deputy Principal Investigator Keith Jahoda. “I hope it is now.
It would help us better understand the results of other X-ray missions.”
Although the observatory would study a variety of high-energy objects, its greatest contribution likely will be in what it can reveal about black holes.
The mission would provide never-before-obtained measurements of how fast black holes spin and how their spin rates affect the curvature of space-time. It also would reveal aspects of how black holes consume and eject matter — data that no other X-ray mission has been able to collect to date.
“This is an important subject in understanding the development of the universe,” Swank said. Although black holes consume copious amounts of matter that orbit too close to their event horizons — the area where the gravitational pull is so strong that nothing can escape — they also eject X-ray-emitting matter back into the universe. “Repopulating space with matter is part of the balance. It plays a key role in the evolution of galaxies,” Swank said. “GEMS will be able to tell us the shapes of the emitting matter better than existing missions can.”
Polarimetry Offers Best Approach
Polarimetry is the best way to obtain this information. Most forms of electromagnetic radiation, including X-rays, radio, and visible light, are a chaotic mixture of waves vibrating in all directions, up and down, side to side, or at any angle perpendicular to the direction from which the wave originated. This is known as unpolarized radiation.
However, if a wave passes through certain materials or is reflected from a surface, like the accretion disk around a black hole, it will vibrate mainly in one direction. This makes it easier to track its origin and its behavior as it interacts with gravitational or magnetic fields. Therefore, measuring polarized X-rays can reveal the geometry of matter as it’s ejected from a black hole, determining whether the matter is confined to a flat disk, puffed into a sphere, or expelled in a jet. No currently available imaging technique can provide the same information.
Until now, the measurement has been impossible to perform, hampered by poor instrument sensitivity and difficulty capturing enough X-ray photons to measure their polarization.
Principal Investigator Jean Swanks (center), Deputy Principal Investigator Keith Jahoda (left), and scientist Kevin Black (right) have won $750,000 to carry out a Phase-A study of the proposed Gravity and Extreme Magnetism SMEX mission. The Agency could select the mission for full development under the Small Explorer program next year. Scientist Phil Deines-Jones is not pictured.
With support from Goddard’s Internal Research and Development program and other NASA R&D funding, however, Goddard scientists Phil Deines-Jones and Kevin Black developed a new technique for measuring X-ray polarization, building the world’s first time-projection chamber polarimeter. Its design allows the capture of more X-ray photons and it measures more precisely their polarization. The polarimeter would be placed at the focus of a grazing-incidence X-ray telescope similar to those on the Japanese-U.S. mission, Suzaku. Goddard’s Peter Serlemitsos and Yang Soong would provide the mirrors.
Black and Deines-Jones have built a flight-like prototype of their polarimeter and expect to finish environmental testing this summer before the team submits its Phase-A report. “It’s the most sensitive technique that anyone knows of for doing this type of science,” Deines-Jones said. “It’s also a unique Goddard capability. We want to make discoveries with it.”
Goddard technologists win new work, secure follow-on funding to mature new technologies, formulate concepts, and validate new instrument concepts in flight demonstrations — successes that benefit Goddard and the scientific community as a whole.