Context : The maximum size of the Galactic stellar disk is not yet known .
Some studies have suggested an abrupt drop-off of the stellar density of the disk at Galactocentric distances R \gtrsim 15 kpc , which means that in practice no disk stars or only very few of them should be found beyond this limit .
However , stars in the Milky Way plane are detected at larger distances .
In addition to the halo component , star counts have placed the end of the disk beyond 20 kpc , although this has not been spectroscopically confirmed so far .

Aims : Here , we aim to spectroscopically confirm the presence of the disk stars up to much larger distances .

Methods : With data from the LAMOST and SDSS-APOGEE spectroscopic surveys , we statistically derived the maximum distance at which the metallicity distribution of stars in the Galactic plane is distinct from that of the halo populations .

Results : Our analysis reveals the presence of disk stars at R > 26 kpc ( 99.7 % C.L . )
and even at R > 31 kpc ( 95.4 % C.L .
) .

Conclusions :