High-resolution , multi-wavelength , and time-domain observations of the Galactic centre black hole candidate , Sgr A* , allow for a direct test of contemporary accretion theory .
To date , all models have assumed alignment between the accretion disc and black hole angular momentum axes , but this is unjustified for geometrically thick accretion flows like that onto Sgr A* .
Instead , we calculate images and spectra from a set of numerical simulations of accretion flows misaligned ( “ tilted ” ) by 15 ^ { \circ } from the black hole spin axis and compare them with millimetre ( mm ) to near-infrared ( NIR ) observations .
Non-axisymmetric standing shocks from eccentric fluid orbits dominate the emission , leading to a wide range of possible image morphologies .
These effects invalidate previous parameter estimates from model fitting , including estimates of the dimensionless black hole spin , except possibly for very low values of spin or tilt ( upper limits of a < 0.3 or \beta < 15 ^ { \circ } ) .
At 1.3 mm , the black hole images still have crescent morphologies , and the black hole shadow may still be accessible to future very long baseline interferometry ( mm-VLBI ) observations .
Shock heating leads to multiple populations of electrons , some at high energies ( T _ { e } > 10 ^ { 12 } K ) .
These electrons can naturally produce the observed NIR flux , spectral index , and rapid variability ( “ flaring ” ) .
This NIR emission is uncorrelated with that in the mm , which also agrees with observations .

These are the first models to self-consistently explain the time-variable mm to NIR emission of Sgr A* .
Predictions of the model include significant structural changes observable with mm-VLBI on both the dynamical ( hour ) and Lense-Thirring precession ( day-year ) timescales ; and \simeq 30 - 50 \mu as changes in centroid position from extreme gravitational lensing events during NIR flares , detectable with the future VLT instrument GRAVITY .
We further predict that multi-wavelength monitoring should find no significant correlations between mm and NIR/X-ray light curves .
The weak correlations reported to date are shown to be consistent with our model , where they are artifacts of the short light curve durations .
If the observed NIR emission is caused by shock heating in a tilted accretion disc , then the Galactic centre black hole has a positive , non-zero spin parameter ( a > 0 ) .