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Map Of Local Space Shows Su'n Lies In Middle Of Hole Piercing Galactic Plane
Nashville - Jun 02, 2003 The first detailed map of space within about 1,000 light years of Earth places the solar system in the middle of a large hole that pierces the plane of the galaxy, perhaps left by an exploding star one or two million years ago. The new map, produced by University of California, Berkeley, and French astronomers, alters the reigning view of the solar neighborhood. In that picture, the sun lies in the middle of a hot bubble -- a region of million-degree hydrogen gas with 100-1,000 times fewer hydrogen atoms than the average gas density in the Milky Way -- and is surrounded by a solid wall of colder, denser gas. Instead, said astronomer Barry Welsh of UC Berkeley's Space Sciences Laboratory, the region around the sun is an irregular cavity of low-density gas that has tunnels branching off through the surrounding dense gas wall. Welsh and his French colleagues suspect that the interconnecting cavities and tunnels, analogous to the holes in a sponge, were created by supernovas or very strong stellar winds that swept out large regions and, when they encountered one another, merged into passageways. "When we started mapping gas in the galaxy, we found a deficit of neutral gas within about 500 light years, suggesting that we are in a bubble-shaped cavity perhaps filled with hot, ionized gas," Welsh said. "But the Local Bubble is shaped more like a tube and should be called the Local Chimney." If this system of interlocking, gaseous cavities is characteristic of the entire galaxy, it presents a dramatic confirmation of a 30-year-old theory of the Milky Way, Welsh said. Welsh is presenting the findings on Thursday, May 29, at the American Astronomical Society meeting in Nashville, Tenn. At the moment, the origin of the cavities is anybody's guess, Welsh said. The local cavity has been around for a few million years and could easily have been caused by a supernova punching through the top and bottom of the galactic disk, the intense stellar winds from 10 or so hot stars, a powerful gamma-ray burst, or even a large star moving through the area. Each of these could theoretically sweep dense gas out of the region, leaving only tenuous, ionized hydrogen. Three recently developed satellites could shed light on the mystery. The Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) satellite, built at UC Berkeley's Space Sciences Laboratory, was launched last December to look for hot, 500,000-degree Celsius gas near our solar system. The UC Berkeley-built SPEAR (Spectroscopy of Plasma Evolution from Astrophysical Radiation) instrument, to be launched later this year as the primary payload of the Korean KAISTSAT-4 satellite mission, will detect the presence of warm gas -- about 250,000 degrees Celsius -- in the solar neighborhood. NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) satellite is also currently searching for this hot gas. With only ground-based telescopes at their disposal, Welsh and his colleagues could not look directly for cold neutral hydrogen (H), since the density is about 10 times too low for radio telescopes to detect. Instead, they looked for a surrogate -- cold neutral sodium, which is found wherever cold, dense hydrogen is found. Using five separate telescopes, they searched for the cavity walls where the density of cold neutral sodium becomes high enough to detect. "We used several ground-based telescopes, including the Observatoire de Haute Provence in France, the European Southern Observatory in Chile and the Lick Observatory in California, to detect atoms of gas in interstellar space towards over a 1,000 nearby stars," said Dr. Rosine Lallement, the project leader at the Centre National de la Recherche Scientifique (CNRS) in Paris. "In collaboration with Dr. Barry Welsh at UC Berkeley, this project has taken over five years to accumulate and analyze all the data."
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