Gould's Belt and Beyond

The motion of OB stars closer than 2 kpc from the Sun is analysed. It shows that the local system of young stars lags behind the LSR by4–5 km s-1, and that its motion may be explained as local nearly rigid-body rotation in the same direction as the overall galactocentric rotation. The residual velocities reveal local expansions in the Scorpius–Centaurus and Orion regions and a motion of these two regions away from each other. The computed orbits show that 10–12 Myr ago the progenitors of Scorpius-Centaurus OB associations were concentrated within a minimum volume. They were also closer to the progenitors of the OB association in Orion, residing all together within a sheet-like region elongated in the ℓ = 20–200° direction. Free expansion, supershells related to OB associations and a supershell related to a hypernova event have been examined as possible models. No agreement with observation has been reached yet; more variants should be tested in the future.