  It is well known that a mixture of two chemical components undergoing one
chemical reaction is a bulk viscous fluid, where the bulk stress evolves
according to the Israel-Stewart theory. Here, we show that a mixture of three
independent chemical components undergoing two distinct chemical reactions can
also be viewed as a bulk viscous fluid, whose bulk stress now is governed by a
second-order differential equation which reproduces the Burgers model for
viscoelasticity. This is a rigorous and physically motivated example of a fluid
model where the viscous stress does not undergo simple Maxwell-Cattaneo
relaxation, and can actually overshoot the Navier-Stokes stress. We show that,
if one accounts for muons, neutron star matter is indeed a bulk viscous fluid
of Burgers type.
