  Hot Jupiters are giant Jupiter-like exoplanets that orbit 100x closer to
their host stars than Jupiter does to the Sun. These planets presumably form in
the outer part of the primordial disc from which both the central star and
surrounding planets are born, then migrate inwards and yet avoid falling into
their host star. It is however unclear whether this occurs early in the lives
of hot Jupiters, when still embedded within protoplanetary discs, or later,
once multiple planets are formed and interact. Although numerous hot Jupiters
were detected around mature Sun-like stars, their existence has not yet been
firmly demonstrated for young stars, whose magnetic activity is so intense that
it overshadows the radial velocity signal that close-in giant planets can
induce. Here we show that hot Jupiters around young stars can be revealed from
extended sets of high-resolution spectra. Once filtered-out from the activity,
radial velocities of V830 Tau derived from new data collected in late 2015
exhibit a sine wave of period 4.93 d and semi-amplitude 75 m/ s, detected with
a false alarm probability <0.03%. We find that this signal is fully unrelated
to the 2.741-d rotation period of V830 Tau and we attribute it to the presence
of a 0.77 Jupiter mass planet orbiting at a distance of 0.057 au from the host
star. Our result demonstrates that hot Jupiters can migrate inwards in <2 Myr,
most likely as a result of planet-disc interactions, and thus yields strong
support to the theory of giant planet migration in gaseous protoplanetary
discs.
