Pictures of Nearby Interstellar Matter

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Structure of Local Interstellar Matter (LISM):

First view (from Space Sciences Reviews, volume 78, page 213, 1996): Structure [gif file]
A second view (in color): Structure [postscript file--unpublished].

Figure 1: Morphology of the interstellar cloud surrounding the Sun, inferred by assuming that the cloud velocity vector is parallel to the surface normal (as would be expected for an expanding superbubble shell), and constrained by LIC column densities (or limits) observed towards Sirius, alpha Cen, and lambda Aql. Cloud multiplicity is based on optical Ca II and ultraviolet observations of Sirius, alpha Cen, and Altair. The two arrows perpendicular to the cloud surface show the direction of motion of the cloud surrounding the solar system. The arrow pointing towards about 4 o'clock shows the motion of the Sun through our neighborhood of the galaxy. This view is of a small section of nearby interstellar gas as it would be viewed from the North Galactic Pole. The center of the galaxy is off the bottom of the picture, 8,000 parsecs away. (One parsec is about equal to three light years.) (The color pictures are by illustrator Christa Wellman.)

A view of the Local Bubble as formed by the Scorpius-Centaurus superbubble expanding into the interarm region surrounding the Sun.

Figure in gif
Figure in postscript)

Figure 2: Illustration of superbubble boundaries projected onto the plane of the galaxy, as sculpted by successive epochs of star formation in the Scorpius-Centaurus Association (SCA) expanding preferentially into the low density interarm region around the Sun. The radius of the figure is 500 pc. The yellow arrow shows the motion of the Sun through our neighborhood of the galaxy. The higher densities of diffuse gas seen within 50 pc of the Sun between galactic longitudes 20 deg and 90 deg represent diffuse gas ablated from the parent molecular cloud complex, including the Aquila Rift, when impacted by the combined stellar winds and supernova shock fronts from star creation and destruction in the SCA. Spiral arm structure is shown by the CO molecular clouds, from Dame et al. (1991, ApJ). Superbubble shell fragments due to epochs of star formation in SCA with the last 15 million years are also shown. The innermost shell in the Scorpius region is the Loop I supernova remnant, while the shell feature at the solar location is from the most recent epoch of star formation in SCA, about 4,000,000 years ago, which formed the bright stars in Scorpius. The shell towards Orion "Orion's Cloak" (Cowie et al. 1979 ApJ) is from a 300,000 supernova in Orion, possibly related to the formation of the Geminga pulsar. The three asterisks show the locations of the three subgroups of star formation in the SCA; these subgroups formed 14-15 million, 11-12 million and 5-6 million years ago. (The color pictures are by illustrator Christa Wellman.)