What lies immediately outside of the heliosphere in the very local interstellar medium (VLISM): morphology of the Local Interstellar Cloud, its hydrogen hole, Stromgren Shells, and 60Fe accretion
Abstract
We describe the very local interstellar medium (VLISM)immediately outside of the outer heliosphere. The VLISM consists of four partially ionized clouds - the Local Interstellar Cloud (LIC), G cloud, Blue cloud, and Aql cloud that are in contact with the outer heliosphere, and ionized gas produced by extreme-UV radiation primarily from the star Epsilon CMa. We construct the three-dimensional shape of the LIC based on interstellar line absorption along 62 sightlines and show that in the direction of Epsilon CMa, Beta CMa, and Sirius B the neutral hydrogen column density from the center of the LIC looking outward is a minimum. We call this region the ``hydrogen hole". In this direction, the presence of Blue cloud absorption and the absence of LIC absorption can be simply explained by the Blue cloud lying just outside of the heliosphere. We propose that the outer edge of the Blue cloud is a Strömgren shell driven toward the heliosphere by high pressures in the H II region. The outer edges of other clouds facing Epsilon CMa are likely also Stromgren shells. Unlike previous models, the LICsurrounds less than half of the heliosphere.We find that the vectors of neutral and ionized helium flowingthrough the heliosphere are inconsistent with the mean LIC flow vector and describe several possible explanations. The ionizationof nearby intercloud gas is consistent with photo-ionization by Epsilon CMa and hot white dwarfs without requiring additional sources of ionization or million degree plasma. In the upwind direction, the heliosphere is passing through an environment of several LISM clouds, which may explain the recent influx of interstellar grains containing 60Fe from supernova ejecta measured in Antarctica snow. The Sun will leave the outer partof the LIC in less than 1900 years, perhaps this year, to either enter the partially ionized G cloud or a highly ionized intercloud layer. The heliosphere will change in either scenario. An instrumented deep space probe sending back in situ plasma and magnetic field measurements from 500-1,000 AU is needed to understand the heliosphere environment rather than integrated data along the sightlines to stars.
- Publication:
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EGU General Assembly Conference Abstracts
- Pub Date:
- May 2020
- DOI:
- 10.5194/egusphere-egu2020-1410
- Bibcode:
- 2020EGUGA..22.1410L