Using the speckle interferometry technique, R136a was shown to be made up of 8 stars within 1 arcsecond at the centre of the cluster, with R136a1 being the brightest.

Its Wide Field and Planetary Camera (WFPC) resolved R136a into at least 12 components and showed that R136 contained over 200 highly luminous stars.

[12] In the night sky, R136 appears as a 10th magnitude object at the core of the NGC 2070 cluster embedded in the Tarantula Nebula in the Large Magellanic Cloud.

[15] R136 is located approximately 157,000 light-years from Earth in the Large Magellanic Cloud, positioned on the south-east corner of the galaxy at the centre of the Tarantula Nebula, also known as 30 Doradus.

[19] Rapid Doppler radial velocity variations would be expected from a pair of equal mass stars in a close orbit, but this has not been seen in the R136a1 spectrum.

This includes ionized nitrogen, helium, carbon, oxygen and occasionally silicon, but with hydrogen lines usually weak or absent.

The emission spectrum is produced in a powerful dense stellar wind, and the enhanced levels of helium and nitrogen arise from convectional mixing of CNO cycle products to the surface.

Higher, less rigid estimates exist, such as an evolutionary mass of 215 M☉ found from HST visual spectra using a non-LTE line-blanketed CMFGEN[21] model atmosphere.

R136a1 closely matches the expected properties for an initially rapidly rotating 251 M☉ star with LMC metallicity after shining for about a million years.

[22] A current mass of 256 M☉ is found in similar analysis using PoWR (Potsdam Wolf–Rayet) atmospheric models[23] with optical and ultraviolet spectra and a mass–luminosity relation,[24] assuming a single star.

This is caused by intense electromagnetic radiation from the very hot photosphere accelerating material away from the surface more strongly than gravity can retain it.

[15] Mass loss is largest for high-luminosity stars with low surface gravity and enhanced levels of heavy elements in the photosphere.

Its brightness at the distance of the nearest star to Earth, Proxima Centauri (just over a parsec), would be about the same as the full moon.

[12] This variation of different colour indices relative to a blackbody is the result of interstellar dust causing reddening and extinction.

EB–V values of 0.29–0.37 have been measured, with considerable uncertainty due to contamination from close neighbours such as R136a2 0.1" away, leading to AV around 1.80 and a de-reddened B–V (B–V0) of −0.30.

The hydrostatic main body of the star is surrounded by a dense atmosphere being accelerated outwards into the stellar wind.

[2][15] R136a1's dimensions are far smaller than the largest stars: red supergiants are several hundred to over a thousand R☉, tens of times larger than R136a1.

In R136a1 it has a FWHM of about 15 Å, indicating a slow or non rotating star, although it could be aligned with its pole facing Earth.

[15] R136a1 is currently fusing hydrogen to helium, predominantly by the CNO cycle due to the high temperatures at the core.

The emission spectrum is created by a dense stellar wind caused by the extreme luminosity, with the enhanced levels of helium and nitrogen being mixed from the core to the surface by strong convection.

The most simplistic accretion models at population I metallicities predict a limit as low as 40 M☉, but more complex theories allow masses several times higher.

The high luminosity, proximity to the Eddington limit, and strong stellar wind, would be likely to create an If* or WNh spectrum as soon as R136a1 became visible as a star.

Helium and nitrogen are rapidly mixed to the surface due to the large convective core and high mass loss, and their presence in the stellar wind creates the characteristic Wolf–Rayet emission spectrum.

The temperature decreases slightly, but the outer layers of the star have inflated, driving even higher mass loss.

The evolution of massive stars depends critically on the amount of mass they can lose, and various models give different results, none of which entirely match observations.

[37] After core helium fusion starts, the remaining hydrogen in the atmosphere is rapidly lost and R136a1 will quickly contract to a hydrogen-free WNE star and the luminosity will decrease.