Stellar nurseries are the massive particle clouds where stars are born from gas and dust in space. These regions, also known as nebulae, are made mostly of hydrogen gas, along with dust and other elements. They are called “nurseries” because, just like in human life, this is where new things begin — in this case, stars.

Inside a stellar nursery, gravity slowly pulls the gas and dust particles together. Over time, as they gather, the material becomes denser and hotter. When a particular area inside the cloud collects enough mass, it starts collapsing in on itself, forming what is known as a **protostar** — the early phase of a star.

As the protostar continues to grow and heat up, nuclear fusion may eventually begin in its core. When this happens, the protostar becomes a main sequence star — a fully formed star that shines by burning hydrogen into helium.

Stellar nurseries are not only beautiful to look at through telescopes, but they are also scientifically important. They help astronomers understand how stars and even solar systems like ours begin.

Let’s break down why the other options are incorrect:
- **Event horizons** are linked to black holes, not star birth.
- **Singularities** are points of infinite gravity at the core of black holes.
- **Star clouds** is a general term and not the specific scientific name.

So the correct term is **Stellar nurseries** — the cosmic cradles of newborn stars.