Cosmic-Ray Energy Density and Pressure in the Local Interstellar Medium from the Voyager Spectra

When Voyager 1 crossed the heliopause it measured, for the first time, the unmodulated spectra of galactic cosmic rays in the surrounding interstellar medium, and integrating those spectra gives the cosmic-ray energy density that the local cloud actually contains. Adopting the published integrated value of 0.90 electronvolts per cubic centimetre, the cosmic-ray pressure is P/k = 3,481 K per cubic centimetre, about 1.66 times the cloud thermal pressure and about a third of the hot bubble interior pressure. Cosmic rays are therefore the largest single support term inside the cloud, and their rough equality with the magnetic pressure is the well-known coincidence now confirmed in the Sun's own neighbourhood. The conversion is computed from the published integrated spectrum with the deposited script.