Thermal Pressure Balance Between the Local Bubble Interior and the Local Interstellar Cloud

The hot interior of the Local Bubble and the warm cloud that surrounds the Sun press against each other across an interface that has never been imaged directly, so the balance between them must be established by arithmetic on published densities and temperatures. Taking an interior temperature of 1.0 million K and the cloud values adopted in the Methods, the interior thermal pressure is P/k = 10,000 K per cubic centimetre against a cloud thermal pressure of only 2,100 K per cubic centimetre, a ratio of 4.8. That thermal-only comparison is misleading, however: adding the cloud magnetic pressure for a three-microgauss field and the cosmic-ray pressure from the Voyager interstellar spectra brings the cloud total to 8,175 K per cubic centimetre, within a factor 1.22 of the interior value. The two phases are therefore close to pressure balance once the full ledger is kept, and the non-thermal terms inside the cloud are not corrections but necessities. The calculation is a computed budget from stated published inputs, not a new measurement, and every number in it can be reproduced from the deposited script.