Expansion Age and Shell Momentum of the Local Bubble from the Measured Surface Velocity

The surface of the Local Bubble is still moving outward, carrying young stars born in its swept-up gas at a mean expansion speed of 6.7 kilometres per second. Dividing the 165-parsec radius by that speed gives a naive expansion age of 24 million years, and correcting for the deceleration expected of an energy-driven bubble, whose radius grows as time to the three-fifths power, gives 14.4 million years. The corrected age sits inside the fourteen-million-year span over which the Scorpius-Centaurus subgroups are reconstructed to have been exploding inside the present bubble volume, and the shell momentum, about 6.7e+06 solar masses times kilometres per second, is of the order that the same number of supernovae delivers. Age and momentum thus corroborate the energy budget from independent directions. The values are computed from stated published inputs with the deposited script.