Specific gas constant
= Specific gas constant
{title2=$\mathcal R$}
The gas constant per unit <mass> for a specified composition. An <ideal gas> obeys $p=\rho\mathcal RT$. With dimensionless <mean molecular weight> $\mu$ relative to an atomic <mass> unit, $\mathcal R=k_B/(\mu m_u)$; the common astrophysical notation $R^*/\mu$ uses a modified mass-based constant rather than the molar gas constant without a <mass> conversion.