Complex sentence: The nature of the central component, R136a, was initially unclear until it was resolved by holographic speckle interferometry and found to be a dense star cluster containing, among other things, twelve very massive and luminous stars in its core.
Split into simpler sentences: The nature of the central component, R136a, was initially unclear. R136a's true nature was resolved by holographic speckle interferometry and found to be a dense star cluster containing, among other things, twelve very massive and luminous stars in its core.