Press release


First mapping of the area surrounding our solar system

Paris, May 29, 2003


Astronomers at the "Service d’Aéronomie" (CNRS, Université Pierre et Marie Curie and the Université de Versailles, Saint Quentin, France), the Observatoire de Paris(1) and the University of California in Berkeley have completed a 3-D map of the area surrounding our solar system. The solar system is inside a "bubble" measuring 1,000 light years in diameter and filled with very dense and hot gas at a temperature of one million degrees. The team revealed, for the first time, a network of "walls" and "tunnels" around this bubble, linking this cavity to other hot gas bubbles surrounding neighboring stars. The purpose of these satellite observations is to enable us to better predict the future evolution of the local bubble. These results are to be announced at the meeting of the American Astronomical Society on May 29, 2003 in Nashville, Tennessee (USA).

An international team of astronomers(2) , led by Rosine Lallement, research director at the CNRS, "Service d’Aéronomie," has created a 3-D reconstruction of the outline of the local interstellar bubble. This is a gigantic cavity in our galaxy, measuring approximately 1,000 light-years in diameter, from which dense gases and dust are absent. Our sun is currently crossing this nearly empty space on its path around the center of the Milky Way. This cavity, one million times bigger than our solar system, was probably created by a series of supernova explosions (or a single explosion of the gamma-ray burst type) over the last several million years. It is also possible that it was blown through "tunnels" by massive stellar winds from the region neighboring Scorpius-Centaurus. The extremely dense gas with which it is filled has a temperature of one million degrees, testimony to its tumultuous past.

The aim of observations obtained with the help of several telescopes, mainly those of the ESO in La Silla, Chile, and also at the Observatoire de Haute-Provence (CNRS), in Australia and in the United States, was to map the region surrounding this local bubble. These observations are based on the search for interstellar sodium atoms in the direction of neighboring stars. When no atom is detected on the path to a star, this means that only a very hot vacuum exists. "When we analyze light coming from a more distant star and we detect a large quantity of sodium instead from areas near the star, this means that we have gone beyond the limit of our local vacuum and that the star is located in the dense galactic environment or in another bubble separated from ours by a dense wall," explains Rosine Lallement who began the project several years ago.

The existence of a network of tunnels and very hot gas bubbles has long been by models: successive supernova explosions produce gigantic expanding bubbles that push gas in front of them, much like a snow plough. The pushed walls run into each other, creating compressed gas shells surrounding the bubbles, broken up in spots. The whole structure looks like foam.

Mapping of the regions surrounding our local bubble is based on observations of the sun, on recent results from the European satellite, Hipparcos, concerning the distances of stars, as well as on new tomographic methods developed by Jean-Luc Vergely, one of the members of the team. Three-D maps show this maze of walls and tunnels linking our cavity to other neighboring hot gas bubbles, like the Lupus-Norma, Scorpius-Centaurus and Auriga-Perseus associations. Computer-generated images will be published soon in the European journal Astronomy & Astrophysics.

"It is not just a question of creating a "roadmap" of our galactic suburbs, but of understanding the physics behind the recycling phenomenon of the interstellar environment as well, and finding an explanation for a number of anomalies," continues Rosine Lallement. The maps show that the local cavity goes through the galactic disk from one end to the other and is extended by two wide tunnels that link it to the galactic corona on the north and south sides. "Using satellite observations with FUSE and Hubble, and a computer-generated analysis of wall movements, we want to test the properties of hot gas in the galactic plane and in these "chimneys" going toward intergalactic space. Are we going to be limited to the inside of a bubble that is getting smaller and smaller, "squeezed" by its neighbors? Or, on the contrary, is there enough pressure in the cavity to overcome these forces and push back the walls?"

Whereas supernova shells are commonly observed, most often at their first stages, just after the explosion, the local bubble is a much calmer and more sprawling "ancestor" and, most importantly, we can observe its interior close up to obtain another type of information. Thanks to this proximity, it is possible, for example, to make a very detailed analysis of the distribution of hot gas emission zones in this bubble as well as their spectral characteristics, which reveal an enormous over-abundance of metals, a property that we find in the "galactic winds" of some galaxies with very high star formation rates that are still not understood. The local bubble may be able to put us on the path to understanding mechanisms that have not been taken into account up until now.

(1) GEPI Laboratory, "Galaxies, Etoiles, Physique et Instrumentation ", CNRS Joint Research Unit, Observatoire de Paris, Université Denis Diderot.
(2) This team includes:
- Rosine Lallement, Service d’Aéronomie, CNRS;
- Jean-Luc Vergely, Société ACRI (Sofia-Antipolis);
- Francoise Crifo, GEPI, Observatoire de Paris, Meudon;
- Barry Welsh, University of California, Berkeley.

Researcher contact:
Rosine Lallement
Service d’Aéronomie.
Tel: +33 1 64 47 42 35

Press contact :
Martine Hasler
Tel: +33 1 44 96 46 35

INSU CNRS contact:
Philippe Chauvin
Tel: +33 1 44 96 43 36 -