UC Berkeley astronomers find a burst cosmic bubble surrounding our own sun

By Robert Sanders, Public Affairs

BERKELEY-- Astronomers at the University of California, Berkeley, have discovered strong evidence that the Local Bubble, a hot, very low-density region of space surrounding our sun, has in fact burst into the galactic halo region.

The finding is further evidence that the hot, million-degree gas seen in galactic halos comes from bubbles like these, which were created originally by exploding stars or supernovas.

The report will be presented today (June 2) at the national meeting of the American Astronomical Society in Chicago by graduate student Daphne Sfeir and research astronomer Barry Welsh, both of the Space Sciences Laboratory at UC Berkeley. (See below for graphic depicting Local Bubble.)

The UC Berkeley scientists, in conjunction with French astronomers, have produced detailed maps of the distribution of cold, neutral interstellar gas within 1,000 light years of the sun. Using measurements of the amount of interstellar sodium gas in the line of sight of 456 nearby stars, they have been able to prove the existence of a "wall" of absorbing, cold gas that surrounds the hot interior of the Local Bubble region.

"These new and exciting results show that not only have we been able to map the actual size and shape of the Local Bubble, but we have also found that the bubble has no defined boundary at all, either above or below the galactic plane," Sfeir said. "Our present observations strongly suggest that the sun actually resides within an open-ended interstellar bubble, or 'Local Tube,' that seems to have burst out into the halo regions of our galaxy."

This picture is confirmed by other data reported at the meeting by Welsh - new maps of the distribution of extreme ultraviolet sources around the sun.

Another paper presented at the AAS meeting today by UC Berkeley astronomer Carl Heiles and University of Wisconsin astronomer Ron Reynolds describes a similar burst bubble in the Milky Way galaxy, a superbubble centered on the Orion nebula that is spewing hot gas into the galactic halo.

The discovery was made during several observing runs in 1998 and 1999 at the Observatoire de Haute Provence in France - the observatory where the first extra-solar planet was discovered. Most of the data was collected by Dr. Rosine Lallement and Dr. Francoise Crifo of the Service d'Aeronomie du CNRS and the Observatoire de Paris-Meudon, France.

The breakthrough in producing accurate maps of local neutral interstellar gas that defines the edges of the Local Bubble region was due to the availability of accurate distances to stars in the sun's neighborhood, which have only recently become available from the Hipparcos satellite.

"Our new galactic maps clearly show the Local Bubble as an empty, highly irregularly-shaped cavity of a radius that varies from about 200 to 700 light years," said Lallement. "In the plane of the galaxy it is surrounded by a wall of dense, neutral interstellar gas, but it seems to have no boundary at all well above and below the galactic plane.

"It is as if the Local Bubble has been squeezed in its middle by the expanding shells of gas associated with the surrounding associations of young stars in Scorpius-Centaurus and Perseus-Taurus. This compression may be why the bubble has burst into the galactic halo and now has no top or bottom."

More detailed results of this work can be found in the upcoming August issue of the "Astronomy and Astrophysics" journal. This work has been supported by the National Aeronautics and Space Administration and the Far Ultraviolet Spectroscopic Explorer mission.

Picture credit: Daphne Sfeir/UC Berkeley

Click here for jpeg image.

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