Answer:
A <u><em>binary </em></u>star system is made of two stars.
An <u><em>open cluster</em></u> star system is made of no more than a few thousand stars.
A <u><em>globular cluster</em></u> star system is made of more than a million stars.
Explanation:
<u><em>A binary star system is made of two stars.</em></u>
A binary Star is a system formed by two gravitationally linked stars, so that they are found spinning around each other (in reality they revolve around a common center of gravity). Binary stars can be very far apart or very close. Sometimes they can exchange material.
<u><em>An open cluster star system is made of no more than a few thousand stars.
</em></u>
Star clusters are clusters of stars that are held together by gravitational effects. All stars belonging to the same cluster have a very similar age. The stars of an open cluster are gravitationally linked to each other, but end up dispersing as they undergo close encounters with other clusters, the interstellar medium, or by interactions between their own stars. Its structure is random and, in general, asymmetric. They are normally made up of young stars with ages of just one million years. They are usually made up of several hundred or thousands of stars.
<u><em>A globular cluster star system is made of more than a million stars.
</em></u>
A globular cluster is a set of hundreds of thousands of gravitationally bound stars. Unlike open clusters, these are much denser (and massive) and their stars exert a much more intense gravitational attraction to each other. They usually contain very old stars. The globular clusters form a halo around our galaxy, the Milky Way, while the open ones are placed in the arms of the spiral. Due to their large number of stars, sometimes in a globular cluster it is difficult to distinguish individual stars.
