7. Star Cloze. Fill in the gaps below.

Word Bank:

Each _____________ in the sky is an enormous glowing ball of gas. The closest star to us is the _____________; our Sun is a medium-sized star. Other than the Sun, the closest star is Proxima Centauri, which is 4.3 _____________ from us.

Stars can live for _____________ of years. A star is born when an enormous cloud of hydrogen gas collapses until it is hot enough to burn nuclear fuel (producing tremendous amounts _____________ and radiation). As the nuclear fuel runs out (in about 5 billion _____________), the star expands while the core contracts; it becomes a giant star that eventually explodes and turns into a dim, cool object (a black dwarf, neutron star, or black hole, depending on its initial mass). The largest stars have the _____________ life span (still billions of years); more massive stars burn hotter and faster than their smaller counterparts (like the Sun).

Stars are giant _____________ reactors. In the center of stars, _____________ are taken apart by tremendous atomic collisions that alter the atomic structure and release an enormous amount of energy. This makes stars hot and bright. In most stars, the primary reaction converts hydrogen atoms into ______________ atoms, releasing an enormous amount of energy.

In the universe, most stars occur in groups of at least ____________ stars. Two stars that are locked in an ______________ orbit around their center of mass (their barycenter) are called a binary star system. About half of all stars are in a binary star system.

There are larger groups of stars, called clusters that are relatively unorganized collections of stars. Huge, organized collections of stars are called _____________. Our Solar System is located in the _____________ Galaxy, a spiral galaxy. All groups of stars are held together by _____________ forces.