The interstellar cloud surrounding the Sun: a new perspective

Abstract

Aims. We offer a new, simpler picture of the local interstellar medium, made of a single continuous cloud enveloping the Sun. This new 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 the ultraviolet 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 cloud that surrounds the Sun in all directions and accounts for most of the matter present in the first 50 parsecs around the Sun. The cloud fills the space around us out to about 9 pc in most directions, although its boundary is very irregular with possibly a few extensions up to 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 inside the cloud vary between 0.03 and 0.1 cm −3 over different directions. Metals appear to be significantly depleted onto grains, and there is a steady increase in depletion from the rear of the cloud to the apex of motion. There is no evidence that changes in the ionizing radiation influence the apparent abundances. Secondary absorption components are detected in 60% of the sight lines. Almost all of them appear to be interior to the volume occupied by the main cloud. Half of the sight lines exhibit a secondary component moving at about −7.2 km s −1 with respect to the main component, which may be the signature of a shock propagating toward the cloud's interior.

Properties of the Interstellar Medium along Sight Lines to Nearby Planet-hosting Stars*

“…However, individual sight line observations cannot constrain where along the sightline the clouds are located or whether the star at the end of the sightline is beyond or embedded within one of the clouds. Redfield & Linsky (2015) confirm that a model of 15 bulk flow clouds is a more accurate characterization of the LISM than a small number of kinematically deformed clouds (Gry & Jenkins 2014).…”

CHARTING THE INTERSTELLAR MAGNETIC FIELD CAUSING THEINTERSTELLAR BOUNDARY EXPLORER(IBEX) RIBBON OF ENERGETIC NEUTRAL ATOMS

“…The CLIC is a decelerating flow of interstellar gas so that cloud collisions supply an opportunity for shock formation (Frisch et al 2002;Linsky et al 2008;Gry & Jenkins 2014;Frisch et al 2015c). Stars that are compliant with B POL are preferentially located in the first galactic quadrant, ℓ=0°-90°( Figure 13).…”

Interstellar Neutral Helium in the Heliosphere from IBEX Observations. VI. The He+ Density and the Ionization State in the Very Local Interstellar Matter

“…The Sun is traversing a cloud of dilute (∼ 0.25 nucleons cm −3 ), warm (∼ 7500 K), partly ionized, magnetized (∼ 3µG) interstellar matter that is an element of a larger cloud structure. This complex cloud is described in the literature either as a set of relatively small individual interstellar clouds (see, e.g., Redfield & Linsky 2008) or a more sizable and complex structure with large-scale internal motions (Frisch et al 2002;Gry & Jenkins 2014). It is located inside the Local Bubble (LB) of low-density (∼ 10 −3 nuc cm −3 ), hot (∼ 1 MK), fully ionized plasma, which most likely formed by overlapping superbubbles from recent nearby supernovae explosions (Frisch et al 2011).…”