R136a2

Lore & Background

In 1960, astronomers at the Radcliffe Observatory in Pretoria cataloged RMC 136, the central 'star' of 30 Doradus, during systematic measurements of bright stars in the Large Magellanic Cloud. Subsequent observations revealed that R136 lies at the center of a giant H II region undergoing intense star formation. In the early 1980s, speckle interferometry resolved R136a into eight components, with R136a2 being marginally the second brightest within one arc-second of the cluster's center. Earlier estimates had suggested that the central region's brightness might require a single star several thousand times the Sun's mass, but the resolution showed a few extremely luminous stars accompanied by many hot O-class stars.

Reader's Guide

R136a2's significance lies in its extreme properties and its role in understanding the upper limits of stellar mass and luminosity. As a Wolf-Rayet star, it undergoes severe mass loss via a fast stellar wind, losing solar masses per year. Its high mass compresses and heats the core, driving hydrogen fusion primarily through the CNO process, producing a luminosity of 5.25 million times the Sun.

The fusion rate is so immense that in ten seconds it generates more energy than the Sun does in a year. Despite its enormous mass, its radius is relatively small, giving it a volume of 41,800 Suns, far smaller than the largest known stars. The star is evolving toward hotter temperatures and is predicted to have started with a mass over a certain threshold.

Its fate is uncertain but likely catastrophic: it is thought that stars this massive cannot lose enough mass to avoid core collapse, resulting in a supernova, hypernova, gamma-ray burst, or possibly almost no visible explosion, leaving behind a black hole. The exact outcome depends on mass loss timing and amount, with current models not fully reproducing observed star and supernova distributions. The most massive stars in the local universe are expected to become hydrogen-free Wolf-Rayet stars before core collapse, producing a Type Ib or Ic supernova and a black hole, with gamma-ray bursts expected only under unusual conditions or for less massive stars.

Did You Know?

• It produces more energy in 10 seconds than the Sun does in a year.
• R136a2 is located in the Large Magellanic Cloud, at a distance of 49.97 kpc.