At least 150 globular clusters inhabit the Milky Way Galaxy. They’re giant balls of stars, and most of them are at least 10 billion years old — the Milky Way’s oldest members. Yet no two are alike. There’s a wide range in size, mass, and how tightly their stars are packed together. One cluster is about 10,000 times the mass of the Sun, and spans more than 150 light-years, so its stars are widely spaced. Another cluster is about two million times the Sun’s mass, but is only a few light-years across. That makes it one of the most tightly packed of all the globulars. That cluster is known as Terzan 5. It’s 19,000 light-years away, on the outskirts of the Milky Way’s core. One of its distinctions is that it contains many pulsars — the ultra-dense cores of once-mighty stars that exploded. A pulsar spins rapidly. One of those in the cluster, in fact, is the fastest in the galaxy — more than 700 revolutions per second. The large number of pulsars may be a result of the cluster’s density. Beca
