Only the 318 in question, however, are close enough to the Milky Way for the predicted galactic speed limit not to have been imposed (300m light years may sound a long way, but it is a short hop on the cosmic scale).
The researchers suggest the clusters they originated from may no longer be active, thus shedding light on the history of star activity in the galactic core.
Seth Shostak, an astronomer at the SETI Institute in California, speculated in 2011 that there could be 30, 000 habitable worlds within 1, 000 light-years of Earth, a minuscule distance by galactic standards.