The trace anomaly of dense matter, $\mathrm{\Delta }\equiv 1/3-P/ϵ$, defined through the ratio $w\equiv P/ϵ$ of pressure $P$ to energy density $ϵ$, quantifies deviations from conformal symmetry and provides a dimensionless measure of the stiffness of the equation of state (EOS) relevant for both neutron stars and heavy-ion collisions. While $\mathrm{\Delta }(ϵ)$ has recently been inferred from neutron star observations, we report the first Bayesian extraction of the trace anomaly from collective flow observables in intermediate-energy heavy-ion collisions. By employing transport-model simulations that explicitly decouple the cold matter mean-field potential from thermal effects, we directly constrain the EOS of cold dense matter. Remarkably, the trace anomaly inferred from laboratory flow data agrees quantitatively, within 68% credible intervals, with independent astrophysical posterior bands. This nontrivial agreement demonstrates that heavy-ion collisions and neutron star observations probe the same macroscopic properties in a mutually consistent way, establishing the dense-matter trace anomaly as a composition-insensitive macroscopic bridge observable across widely different physical environments.

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• Low & intermediate energy heavy-ion reactions
• Nuclear matter in neutron stars
• Nuclear reactions