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The spherical Jeans equation is a widely used tool for dynamical study ofgravitating systems in astronomy. Here we test its efficacy in robustlyweighing the mass of Milky Way analogues, given they need not be in equilibriumor even spherical. Utilizing Milky Way stellar halos simulated in accordancewith $\Lambda{\rm CDM}$ cosmology by Bullock and Johnston (2005) and analysingthem under the Jeans formalism, we recover the underlying mass distribution ofthe parent galaxy, within distance $r/{\rm kpc}\in[10,100]$, with a bias of$\sim12\%$ and a dispersion of $\sim14\%$. Additionally, the mass profiles oftriaxial dark matter halos taken from the SURFS simulation, within scaledradius $0.2<r/r_{\rm max}<3$, are measured with a bias of $\sim-2.4\%$ and adispersion of $\sim10\%$. The obtained dispersion is not because of Poissonnoise due to small particle numbers as it is twice the later. We interpret thedispersion to be due to the inherent nature of the $\Lambda{\rm CDM}$ halos,for example being aspherical and out-of-equilibrium. Hence the dispersionobtained for stellar halos sets a limit of about $12\%$ (after adjusting forrandom uncertainty) on the accuracy with which the mass profiles of the MilkyWay-like galaxies can be reconstructed using the spherical Jeans equation. Thislimit is independent of the quantity and quality of the observational data. Thereason for a non zero bias is not clear, hence its interpretation is notobvious at this stage.

Jeans that fit: weighing the mass of the Milky Way analogues in the $\Lambda{\rm CDM}$ universe