GEMS

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GEMS will use an X-ray telescope to measure the polarization of the X-rays coming from the vicinity of compact objects in the universe: black holes and neutron stars and it will also study the remnants of massive stars which have exploded as supernovae. Few polarization measurements have been made in X-ray astronomy since the 1970’s and so GEMS is expected to break new ground. The polarization depends, in part, on the X-ray scattering in the accretion disk around the compact object in a binary star system, and so GEMS will help to constrain the geometry in such systems. GEMS may also help to constrain the shape of space that has been distorted by a spinning black hole's gravity, and probe the structure and effects of the formidable magnetic field around magnetars, dead stars with magnetic fields trillions of times stronger than Earth's.

GEMS may therefore help to explain:

• How spinning black holes affect space-time and matter as it is drawn in and compressed by strong gravitational fields.
• What happens in the super strong magnetic fields near pulsars and magnetars.
• How cosmic rays are accelerated by shocks in supernova remnants.

Using GEMS, astronomers will be able to improve their knowledge of the shapes of the X-ray-emitting matter trapped near black holes -- in particular, whether matter around a black hole is confined to a flat disk or puffed into a sphere or squirting out in a jet. Since X-rays are polarized by the space swirling around a spinning black hole, GEMS also provides a method of helping to constrain black hole spin independent of other techniques.

The heart of GEMS is a small chamber filled with gas. When an X-ray is absorbed in the gas, an electron carries off most of the energy, and starts out in a direction related to the polarization direction of the X-ray. This electron loses energy by ionizing the gas; the instrument measures the direction of the ionization track, and thereby the polarization of the X-ray. The GEMS detector readout employs a 'time projection chamber' to make an image of the track.

NASA's Goddard Space Flight Center, Greenbelt, Maryland, will be responsible for the GEMS instrument and the overall program management. Orbital Sciences Corporation, Dulles, Va., will be responsible for building the spacecraft and mission operations. ATK Space, Goleta, Calif., will build a boom to place the X-ray telescopes the proper distance from the detectors. NASA's Ames Research Center, Moffett Field, Calif., will assist the project by providing EPO support and Co-I's.

The University of Iowa will provide instrument calibration assistance, and will have students prepare an experiment that could be part of the mission. GEMS includes collaborators from universities including MIT, Johns Hopkins University, Cornell University, Rice University, the University of Oulu (Finland), North Carolina State University and Washington University.

Last Updated Date: March 16, 2012