Here, the high density of stars means that at any given time several could be exploding, frying off a planet's ozone layer and exposing any surface life to deadly ultraviolet rays. (sciencemag.org)
Most of those detected are located in nearby star forming regions, which are all fairly small and have a low density of stars. (sciencedaily.com)
However, clusters that form with a higher density of stars can stay together for much longer. (sciencedaily.com)