  There is a unique unitarily-invariant ensemble of $N\times N$ Hermitian
matrices with a fixed set of real eigenvalues $a_1 > \dots > a_N$. The joint
eigenvalue distribution of the $(N - 1)$ top-left principal submatrices of a
random matrix from this ensemble is called the orbital unitary process. There
are analogous matrix ensembles of symmetric and quaternionic Hermitian matrices
that lead to the orbital orthogonal and symplectic processes, respectively. By
extrapolation, on the dimension of the base field, of the explicit density
formulas, we define the orbital beta processes. We prove the universal behavior
of the virtual eigenvalues of the smallest $m$ principal submatrices, when $m$
is independent of $N$ and in such a way that the rescaled empirical measures
converge weakly. The limiting object is the Gaussian beta corners process. As a
byproduct of our approach, we prove a theorem on the asymptotics of
multivariate Bessel functions.
