Electromagnetic radiation analysis is one of the main methods scientists employ to study the far reaches of the universe. In theory, there are four ways to observe electromagnetic radiation. One of these, however, a technique known as polarimetry, has remained out of reach for researchers who focus on x-ray astronomy. Now a new instrument described in today's issue of the journal Nature could finally change that.
Electromagnetic radiation consists of photons. So far, researchers probing x-ray sources have succeeded in counting the photons and assessing the direction and the energy and frequency of photons from these sources. But efforts to measure polarization at x-ray wavelengths have failed. Italian researchers Enrico Costa and Ronaldo Bellazzini and their colleagues have thus developed a special machine for the task. Somewhat similar to a Geiger counter in design, the device features a gas-filled chamber. As an x-ray enters the chamber it interacts with the gas, producing an energetic photoelectron. The instrument then measures both the presence of the electron and the path it travels. Because this path is determined by the original photon's electromagnetic field, it reveals the linear polarization of the x-ray.
Placed at the focus of a large x-ray telescope in orbit, the team notes, this "polarimeter" could give completely new insights into the geometry of x-ray-emitting sources such as quasars and black holes. "Perhaps when Costa, Bellazzini and their colleagues loft the first of their efficient polarimeters above the atmosphere they will be able to detect polarization in unexpected placesmaybe from the surfaces of thermal neutron stars, or even from interstellar shocks that arise when high-speed plasma collides with quieter regions of cooler gas," University of Colorado researcher Webster Cash writes in a commentary accompanying the Nature report. "We can all hope that this new device will follow the established pattern of invention and discovery, making observations that will change our understanding of the cosmos."