In any globular cluster, all its stars formed at the same time, from the same cloud of gas. The Milky Way has around 150 known globular clusters; these objects are excellent tools for studying, for example, the history of the Universe, or the dark matter content of the galaxies they orbit.

Scientists say microscopic black holes could explain the elusive "dark matter" that makes up a quarter of all matter in the universe. But can it be proven?

If microscopic black holes born a fraction of a second after the Big Bang exist, then at least one may fly through the solar system per decade, generating tiny gravitational distortions that scientists can detect.