  Gamma-ray observations have established energetic isolated pulsars as
outstanding particle accelerators and antimatter factories in the Galaxy. There
is, however, no consensus regarding the acceleration mechanisms and the
radiative processes at play, nor the locations where these take place. The
spectra of all observed gamma-ray pulsars to date show strong cutoffs or a
break above energies of a few gigaelectronvolt (GeV). Using the H.E.S.S. array
of Cherenkov telescopes, we discovered a novel radiation component emerging
beyond this generic GeV cutoff in the Vela pulsar's broadband spectrum. The
extension of gamma-ray pulsation energies up to at least 20 teraelectronvolts
(TeV) shows that Vela pulsar can accelerate particles to Lorentz factors higher
than $4\times10^7$. This is an order of magnitude larger than in the case of
the Crab pulsar, the only other pulsar detected in the TeV energy range. Our
results challenge the state-of-the-art models for high-energy emission of
pulsars while providing a new probe, i.e. the energetic multi-TeV component,
for constraining the acceleration and emission processes in their extreme
energy limit.
