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. Because stars are so close together, collisions may be common. That causes more supernova explosions, which create pulsars — among the most interesting residents of this giant “city” of stars.

Terzan 5 is in Sagittarius. It climbs into good view, in the southeast, after midnight, and is low in the south-southwest at first light. Its stars form the outline of a teapot. Terzan 5 is above the spout — in the “steam” of the Milky Way.
 

Script by Damond Benningfield

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