R136a3
R136a3 is a Wolf–Rayet star in R136, a massive star cluster located in Dorado. It is located near R136a1, the most massive and luminous star known. R136a3 is itself one of the most massive and most luminous stars known at about 154 times more massive and 4.3 million times more luminous than the Sun. The formal name of the star is RMC 136a3, standing for "Radcliffe observatory, Magellanic Clouds, 136a3". The RMC survey identified luminous objects in the Large Magellanic Cloud and one of the brightest was RMC 136. This is now commonly shortened to R136, which is  now known to be an extremely young dense open cluster at the core of the NGC 2070 cluster in the Tarantula Nebula. R136 was eventually resolved and the brightest "star" at the centre was termed R136a. This was further resolved into multiple components, one of which is R136a3. Although R136a3 has a Wolf-Rayet spectral type dominated by intense emission lines of helium and nitrogen, usually indicating a highly evolved star that has lost its outer layers, R136a3 is actually an extremely young star. The spectrum also includes hydrogen lines and analysis shows the star is still 40% hydrogen at  the surface. The helium and nitrogen in the atmosphere of such a young star are caused by strong convection due to the massive core and intense CNO cycle fusion, enhanced further by rotational mixing. The emission lines in the spectrum indicate strong mass loss caused by the fusion products at the surface and the enormous luminosity.