Clouds that Give Birth to Stars

Nebulae are relatively widely-known as astronomical figures, but this was not always the case – rather, the term was indistinct, referring to a wide range of celestial objects. In fact, even into the early twentieth century, the term referred to those distant objects that we now know are whole galaxies.

Despite this early confusion, nebulae were always notable as objects to those cultures that paid close attention to the night sky. The earliest records of them as such come from the Maya and the Greeks, who noted that some areas of the sky appeared to glow with a diffuse light, as if many tiny stars were clustered in a small region. It was, however, many centuries before their true nature could be correctly defined.

There are three broad types of nebula, according to their ‘emissions’, which is to say, how they behave in accordance with light. Absorption (or ‘dark’) nebulae are clouds without stars within or nearby, and thus are characterised by their dampening effect on the light from stars beyond. Reflection nebulae have nearby stars whose light illuminates the gases of the nebula. The final, and more interesting kind, are called emission nebulae, and are the birthplaces of stars and planets.

Emission nebulae are regions of space in which matter comes together, forming dense pockets that, following all of the usual laws of gravity, gather other matter into themselves. As these gain further mass, their relative gravity continues to increase, faster and faster with the increase of mass and, thus, gravity. In the fullness of time, these pockets gain so much mass that the gravity holding it in place, condensing matter into such a confined space, results in the ignition of the matter, thus giving birth to a star.

If this were not enough, emission nebulae are also among the most beautiful of all astronomical phenomena – the Orion Nebula and Carina Nebula are worthy of special mention, while the Trifid Nebula is composed of emission, reflection and absorption nebulae, creating its wondrous lobed structure.