New radio map of Milky Way's center.

From a monster black hole to mysterious filaments of gas, the center of the Milky Way offers astronomers a wide variety of attractions. Now, researchers have produced the largest and most detailed radio-wavelength atlas of the galactic center.

The image is based on a new computer analysis of observations taken a decade ago with the Very Large Array (VLA), a network of 27 radio telescopes near Socorro, N.M. By more accurately accounting for the geometry of this Y-shaped telescope array, astronomers sharpened a previous radio map generated from observations made at a wavelength of 90 centimeters.

At this wavelength, notes Namir E. Kassim of the Naval Research Laboratory in Washington, D.C., radio telescopes can detect two very different types of emissions: ionized gas heated by hot stars and high-speed electrons accelerated by the strong magnetic fields found at the galactic center.

In the high-resolution map, Kassim and his colleagues found the second-closest supernova remnant to the galaxy's center. Known as SNR 0.3+.0.0, the remnant--an expanding shell of gas hurled into space by a supernova explosion--lies about 150 light-years from the Milky Way's core.

Kassim and Dale A. Frail of the National Radio Astronomy Observatory in Socorro discovered a large filament, dubbed the pelican because of its shape when viewed in an enlarged image. At about 1,000 light-years from the center of the galaxy, the pelican is the most distant filament from the core and the only one aligned with the plane of the galaxy. All other filaments are aligned perpendicular to the plane.

Like iron filings, the orientations of the filaments are presumed to trace the direction of the magnetic field at the core. Kassim suggests that the pelican has a different alignment because the galactic magnetic field has changed direction in that outlying region.

Radio astronomers including Kassim are now taking a new set of VLA observations at the 90-cm wavelength. Their goal is to determine if any of the radio sources has changed since the original data were recorded in 1989. Simultaneously, the team is constructing the first radio map ever recorded at a wavelength of 4 meters. Astronomers are hoping that the 4-m map, which should show details not apparent at shorter wavelengths, will turn out to be as important a touchstone for explorers of the galactic center as the 90-cm map has already become.