Nature has been putting up lots of interesting science lately on its site. (Maybe you checked out the nanotech material from Nature which I posted below?) Well, this latest article concerns the shapes and movements of black holes and neutron stars.

If anybody thinks the pace of science is slowing, perhaps it's just catching its breath?

http://www.nature.com/nsu/010607/010607-10.html

Space: A hole lot of twisting
TOM CLARKE

Astronomers have a new tool for peering into the hearts of massive neutron stars and mysterious black holes. The device measures the twisting, or polarization, of the X-rays given off by these energetic, yet elusive objects and could help to resolve their shapes and movements1.

Neutron stars and especially black holes are so dense that they don't give off visible light, but these objects' interactions with the matter surrounding them produce large amounts of high-energy X-rays that betray their presence.

Because it moves as a wave, a photon of light (or in this case of X-rays) viewed head-on travels in a particular plane — up-and-down, side-to-side or anywhere in between — called its 'polarization angle'. Any given group of photons has a random mix of polarization angles. But certain events can align the photons — and studying the degree of alignment in X-rays from certain sources can yield useful information.

For example, X-rays from objects such as rotating neutron stars or black holes can have their polarization angle twisted by the gravitational pull of the object, its magnetic field, or by colliding with matter surrounding it. But so far, astronomers have only been able to measure the brightness and wavelength of X-rays from these distant sources.

Using the new device, called a micro-pattern gas chamber (MPGC), "we should be able to get information from the inner parts of these systems", says Enrico Costa an X-ray astronomer at the Instituto di Astrofisica Spaziale, in Rome, Italy, who developed the prototype instrument.

By sifting through the various polarizations of X-rays, the detector should allow astronomers to make inferences about the shapes and movements of invisible phenomena such as the gravitational and magnetic fields of distant objects. "This tool will fill in some of the many missing pieces," says Webster Cash an X-ray astronomer at the University of Colorado in Boulder.

Costa's team, in collaboration with particle physicists at Italy's Instituto Nazionale di Fisica Nucleare in Pisa, developed the MPGC to detect the polarization of every X-ray photon that passes through it.

Each photon entering the instrument interacts with a mixture of neon and dimethyl ether gas sealed within it, much as a Geiger counter counts radioactive particles. But an array of tiny detectors then tracks the paths of electrons given off by the interactions. The path of an emitted electron is directly related to the polarization angle of the X-ray particle as it entered the detector.

"It's well-known physics combined with new technology," says Costa.

The MPGC works well on the bench-top. But before it starts probing the outer reaches of the cosmos it will need to be connected to sophisticated optics — to channel distant X-rays into it — and then launched into space. Cash believes that "a fairly straightforward adaptation" should make the prototype ready for launch and Costa's team hopes to see their detector in orbit within a decade.

Costa, E. et al. An efficient photoelectric X-ray polarimeter for the study of black holes and neutron stars. Nature 411, 662–665 (2001).

© Macmillan Magazines Ltd 2001 - NATURE NEWS SERVICE