Discovery of a massive giant planet with extreme density around a sub-giant star TOI-4603

We present the discovery of a transiting massive giant planet around TOI-4603, a sub-giant F-type star from NASA's Transiting Exoplanet Survey Satellite (TESS). The newly discovered planet has a radius of \(1.042^{+0.038}_{-0.035}\) \(R_{J}\), and an orbital period of \(7.24599^{+0.00022}_{-0.00021}\) days. Using radial velocity measurements with the PARAS {and TRES} spectrographs, we determined the planet's mass to be \(12.89^{+0.58}_{-0.57}\) \(M_{J}\), resulting in a bulk density of \(14.1^{+1.7}_{-1.6}\) g \({cm^{-3}}\). This makes it one of the few massive giant planets with extreme density and lies in the transition mass region of massive giant planets and low-mass brown dwarfs, an important addition to the population of less than five objects in this mass range. The eccentricity of \(0.325\pm0.020\) and an orbital separation of \(0.0888\pm0.0010\) AU from its host star suggest that the planet is likely undergoing high eccentricity tidal (HET) migration. We find a fraction of heavy elements of \(0.13^{+0.05}_{-0.06}\) and metal enrichment of the planet (\(Z_{P}/Z_{star}\)) of \(4.2^{+1.6}_{-2.0}\). Detection of such systems will offer us to gain valuable insights into the governing mechanisms of massive planets and improve our understanding of their dominant formation and migration mechanisms.