Why are nebulae called the cradles of stars?

"Star nursery" is not a poetic phrase dreamed up by sellers of stardust: it is the term astronomers use themselves. Stars really are born inside nebulae. Here is how, in three simple steps.

1. A cloud of gas and dust

Between the stars, space is not empty: it holds interstellar gas, mostly hydrogen, along with cosmic dust. In places this mixture gathers into immense clouds several light-years wide, and those are nebulae. Some of them glow, since ionized hydrogen emits that characteristic pink light; others reflect the light of nearby stars; others still stand out as dark silhouettes.

2. Gravity does its work

In the densest regions of the cloud, gravity wins: matter collapses in on itself, heats up and begins to swirl. At the heart of these cocoons the temperature climbs for hundreds of thousands of years, right up to the magic threshold.

3. A star ignites

When the core reaches several million degrees, hydrogen fusion begins and a star is born. Its new light then sculpts the very cloud that produced it, and that is how the Pillars of Creation took shape in the Eagle Nebula: columns of gas light-years tall, photographed first by Hubble and then by James Webb.

Nurseries you can look at tonight

The Orion Nebula can be glimpsed with the naked eye below Orion's belt on winter evenings, and the Lagoon can be picked out with binoculars in Sagittarius on a summer night. Our own Sun was born 4.6 billion years ago inside a nebula that has long since dispersed: every atom in your body once passed through one of these cradles.

It is that symbolism, birth, beginning, cosmic lineage, that makes nebulae such a singular gift. Symbolically dedicating a fragment of a star nursery to someone you love is a way of wishing them a beginning. The most famous cradles are in theEonelya collection, in authentic photographs.

Sources: ESA/Hubble, Star formation ·NASA, Stars.