We return to the topic of the humble globular cluster, an object that usually draws little attention as it consists of a clump of about a million very dim stars. One aspect of globular clusters that is interesting is that all of these stars are enclosed in an incredibly small space.
As an analogy, imagine substituting stars in the sky with administrators in an office. Let us say that your task is to house 10 administrators You could choose to give them each their own desk space in a large room, or you could to save on space and crush them all into a small elevator for eight hours per day.
The former case is similar to that of the Milky Way. In the Milky Way, each star (administrator) is sitting in a part of sky (a desk) that is spaced a comfortable distance from the other stars (administrators). Thus when we look up at the sky at night, we do see other stars (administrators), but apart from the Sun the other stars do not look so piercingly bright and close to us.
The latter case, on the other hand, is similar to that of the globular cluster. Here each star (administrator) in the globular cluster is pressed uncomfortably against another star (administrator). The stars are so compactly arranged that if Earth would be magically relocated to the inside of a globular cluster there would be no night time. We would see many “suns” in the daytime and many “suns” at night.
What might be the benefit of such a crowded arrangement of stars as one finds in a globular cluster? One recent fascinating discovery is that binary black holes can form in globular clusters more readily than in most other environments.
Of the sets of binary black holes that are situated in globular clusters, some of them will emit powerful radio jets that shoot out of the globular cluster. We are just starting to detect these jets at radio frequencies, and as the data come in, there is just no other explanation that we can come up with apart from the probably presence of a binary black hole!