The dense star cluster called R136 is located within the Tarantula Nebula (also known as 30 Doradus), a giant star-forming region in a nearby dwarf galaxy. Astronomers suspect that the multiple clumps of stars within R136 are actually a pair of interacting star clusters. Supporting evidence for this idea comes from the large number of “runaway stars” — stars moving with unusually high velocity — that have been found within the nebula. A single, large star cluster would not produce as many runaway stars as two smaller interacting star clusters. In addition, some of these runaway stars are older than the estimated age of R136.
This computer simulation shows the gravitational interaction of two young star clusters. The 3.5 million years of the encounter have been compressed into just 27 seconds. The smaller star cluster approaches from the left, has its trajectory bent strongly as it swings by the larger cluster, and then returns for a second pass. The visualization then zooms in and dissolves to a Hubble Space Telescope image of star cluster R136. After a partial zoom out, the sequence continues forward in time to show the clusters merging into a single cluster.
At the start of the simulation, the smaller cluster is not gravitationally bound to the large cluster. After the first interaction, the pair of star clusters become gravitationally entwined and destined to merge together. A noticeable byproduct of the encounter is that interactions between stars efficiently eject massive stars from the smaller cluster. Some of these ejected stars would be considered runaways. Further, the stars in the smaller cluster are a million years older than those in the larger cluster, which would help explain the observed age discrepancies. Finally, note that while all the stars shown are initially hot and blue, some reach the end of their lives during the simulation and evolve into cooler red giant stars.
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