Supervirial

For example, the 0.5-2 Myr old Orion Nebula Cluster ( ONC ), which is known to be supervirial with a virial mass about twice the observed mass ( Hillenbrand & Hartmann 1998 ), has already expelled its residual gas and is expanding rapidly.

For many of the young (~10Myr) star clusters M_(dyn) >> Mₚₕₒₜ Goodwin & Bastian (2006) suggest that this is a signature of gas expulsion and the 'infant mortality' scenario discussed in Section 2.1, i.e., they conclude that these clusters are supervirial.

If measured early enough (lt;2 Myr in our simulations, or #92;sim20 crossing times), the velocity dispersion can be used to determine whether a region was highly supervirial at birth without the risk of degeneracy.

It is subvirial when Q < 1, which corresponds to a negative acceleration of the polar inertia moment, Ï < 0 (initial contraction) and supervirial when Q >1, which corresponds to a positive acceleration of the polar inertia moment, Ï > 0 (initial expansion).