  Stars form by accreting material from their surrounding disks. There is a
consensus that matter flowing through the disk is channelled onto the stellar
surface by the stellar magnetic field. This is thought to be strong enough to
truncate the disk close to the so-called corotation radius where the disk
rotates at the same rate as the star. Spectro-interferometric studies in young
stellar objects show that Hydrogen is mostly emitted in a region of a few
milliarcseconds across, usually located within the dust sublimation radius. Its
origin is still a matter of debate and it can be interpreted as coming from the
stellar magnetosphere, a rotating wind or a disk. In the case of
intermediate-mass Herbig AeBe stars, the fact that the Br gamma emission is
spatially resolved rules out that most of the emission comes from the
magnetosphere. This is due to the weak magnetic fields (some tenths of G)
detected in these sources, resulting in very compact magnetospheres. In the
case of T Tauri sources, their larger magnetospheres should make them easier to
resolve. However, the small angular size of the magnetosphere (a few tenths of
milliarcseconds), along with the presence of winds emitting in Hydrogen make
the observations interpretation challenging. Here, we present direct evidence
of magnetospheric accretion by spatially resolving the inner disk of the 60 pc
T Tauri star TW Hydrae through optical long baseline interferometry. We find
that the hydrogen near-infrared emission comes from a region approximately 3.5
stellar radii (R*) across. This region is within the continuum dusty disk
emitting region (Rcont = 7 R*) and smaller than the corotation radius which is
twice as big. This indicates that the hydrogen emission originates at the
accretion columns, as expected in magnetospheric accretion models, rather than
in a wind emitted at much larger distance (>1au).
