  The centre of the Milky Way hosts a supermassive black hole of 4 million
solar masses called Sagittarius A*. This object has been observed for more than
20 years in the near infrared. This has confirmed some effects of General
Relativity. In addition, recurrent observations have made it possible to detect
flares, i.e. a much larger flux than the average, with a variability of the
order of 30 minutes to 1 hour. In 2018, GRAVITY, using the 4 large telescopes
of the VLTI/ESO, observed an orbital motion of the source of these flares. This
thesis focuses on the modelling of these flares, using models of varying
complexity, including one based on the phenomenon of magnetic reconnection. The
latter corresponds to an abrupt change in the magnetic configuration around the
black hole, releasing a large amount of energy. We are also looking at the
problem of polarisation in General Relativity.
