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Journal Articles Astronomy and Astrophysics - A&A Year : 2014

The interstellar cloud surrounding the Sun: a new perspective

Cécile Gry


We offer a new, simpler picture of the local interstellar medium, made of a single continuous cloud enveloping the Sun. Thisnew outlook enables the description of a diffuse cloud from within and brings to light some unexpected properties.Methods.We re-examine the kinematics and abundances of the local interstellar gas, as revealed by the published results for theultraviolet absorption lines of Mg II, Fe II, and H I.Results.In contrast to previous representations, our new picture of the local interstellar medium consists of a single, monolithic cloudthat surrounds the Sun in all directions and accounts for most of the matter present in the first 50 parsecs around the Sun. The cloudfills the space around us out to about 9 pc in most directions, although its boundary is very irregular with possibly a few extensions upto 20 pc. The cloud does not behave like a rigid body: gas within the cloud is being differentially decelerated in the direction of motion,and the cloud is expanding in directions perpendicular to this flow, much like a squashed balloon. Average H I volume densities insidethe cloud vary between 0.03 and 0.1 cm−3over different directions. Metals appear to be significantly depleted onto grains, and thereis a steady increase in depletion from the rear of the cloud to the apex of motion. There is no evidence that changes in the ionizingradiation influence the apparent abundances. Secondary absorption components are detected in 60% of the sight lines. Almost all ofthem appear to be interior to the volume occupied by the main cloud. Half of the sight lines exhibit a secondary component movingat about−7.2km s−1with respect to the main component, which may be the signature of a shock propagating toward the cloud’sinterior.
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insu-03466607 , version 1 (06-12-2021)




Cécile Gry, Edward Jenkins. The interstellar cloud surrounding the Sun: a new perspective. Astronomy and Astrophysics - A&A, 2014, 567, pp.A58. ⟨10.1051/0004-6361/201323342⟩. ⟨insu-03466607⟩
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