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Abstract: The neutral interstellar medium ISM inside the Local Bubble LB has beenknown to have properties typical of the warm neutral medium WNM. However,several recent neutral hydrogen HI absorption experiments show evidence forthe existence of at least several cold diffuse clouds inside or at the boundaryof the LB, with properties highly unusual relative to the traditional coldneutral medium. These cold clouds have a low HI column density, and AU-scalesizes. As the kinematics of cold and warm gas inside the LB are similar, thissuggests a possibility of all these different flavors of the local ISMbelonging to the same interstellar flow. The co-existence of warm and coldphases inside the LB is exciting as it can be used to probe the thermalpressure inside the LB. In addition to cold clouds, several discrete screens ofionized scattering material are clearly located inside the LB.The cold exotic clouds inside the LB are most likely long-lived, and weexpect many more clouds with similar properties to be discovered in the futurewith more sensitive radio observations. While physical mechanisms responsiblefor the production of such clouds are still poorly understood, dynamicaltriggering of phase conversion and-or interstellar turbulence are likely toplay an important role.

Author: Snezana Stanimirovic UW Madison

Source: https://arxiv.org/

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