  The Vicsek model encompasses the paradigm of active dry matter. Motivated by
collective behavior of insects in swarms, we have studied finite size effects
and criticality in the three dimensional, harmonically confined Vicsek model.
We have discovered a phase transition that exists for appropriate noise and
small confinement strength. On the critical line of confinement versus noise,
swarms are in a state of scale-free chaos characterized by minimal correlation
time, correlation length proportional to swarm size and topological data
analysis. The critical line separates dispersed single clusters from confined
multicluster swarms. Scale-free chaotic swarms occupy a compact region of space
and comprise a recognizable `condensed' nucleus and particles leaving and
entering it. Susceptibility, correlation length, dynamic correlation function
and largest Lyapunov exponent obey power laws. The critical line and a narrow
criticality region close to it move simultaneously to zero confinement strength
for infinitely many particles. At the end of the first chaotic window of
confinement, there is another phase transition to infinitely dense clusters of
finite size that may be termed flocking black holes.
